linux-wallpaperengine-kde/src/WallpaperEngine/Render/Objects/CParticle.cpp

#include "CParticle.h"

#include "WallpaperEngine/Data/Model/Property.h"
#include "WallpaperEngine/Logging/Log.h"
#include "WallpaperEngine/Maths.h"
#include "WallpaperEngine/Render/Utils/NoiseUtils.h"

#include <GL/glew.h>
#include <algorithm>
#include <cmath>
#include <glm/gtc/constants.hpp>
#include <glm/gtc/matrix_transform.hpp>

extern float g_Time;
extern float g_RealTime;

using namespace WallpaperEngine::Render::Objects;
using namespace WallpaperEngine::Render::Utils;
using namespace WallpaperEngine::Data::Model;

CParticle::CParticle (Wallpapers::CScene& scene, const Particle& particle) :
    CObject (scene, particle), CRenderable (scene, particle, *particle.material->material),
    ScriptableObject (scene, particle), m_particle (particle) {
    this->registerProperty ("scale", *particle.scale->value);
    this->registerProperty ("angles", *particle.angles->value);
    this->registerProperty ("visible", *particle.visible->value);
    this->registerProperty ("parallaxDepth", *particle.parallaxDepth->value);

    this->detectTexture ();
    std::random_device rd;
    m_rng.seed (rd ());

    // Read renderer config early - buffer sizing below depends on it
    if (!m_particle.renderers.empty ()) {
	const auto& renderer = m_particle.renderers[0];
	if (renderer.name == "rope" || renderer.name == "ropetrail") {
	    // Both rope and ropetrail use genericropeparticle shader
	    m_useRopeRenderer = true;
	    m_ropeSubdivision = std::max (0, static_cast<int> (renderer.subdivision));
	    m_ropeUVScale = renderer.uvScale;
	    m_ropeUVScrolling = renderer.uvScrolling;
	    m_ropeUVSmoothing = renderer.uvSmoothing;

	    if (renderer.name == "ropetrail") {
		m_useTrailRenderer = true;
		m_trailLength = renderer.length;
		m_ropeSegments = std::max (2, static_cast<int> (renderer.segments));
	    }
	} else if (renderer.name == "spritetrail") {
	    // spritetrail uses genericparticle with TRAILRENDERER combo
	    m_useTrailRenderer = true;
	    m_trailLength = renderer.length;
	    m_trailMaxLength = renderer.maxLength;
	    m_trailMinLength = renderer.minLength;
	}
    }

    float countMultiplier = particle.instanceOverride.count->value->getFloat ();
    uint32_t adjustedMaxCount = static_cast<uint32_t> (particle.maxCount * countMultiplier);

    // Use wallpaper's specified count, or default if maxCount is 0
    m_maxParticles = (adjustedMaxCount > 0) ? adjustedMaxCount : DEFAULT_MAX_PARTICLES;

    m_particles.resize (m_maxParticles);

    if (m_useRopeRenderer) {
	// Rope: N particles connect via (N-1) segments, each subdivided into sub-segments
	const int subdivision = std::max (1, m_ropeSubdivision);
	const int maxSubSegments = std::max (1, static_cast<int> (m_maxParticles - 1)) * subdivision;
	m_vertices.resize (maxSubSegments * 4 * ROPE_FLOATS_PER_VERTEX);
	m_indices.resize (maxSubSegments * 6);
    } else {
	// 4 vertices, 6 indices per particle
	const int verticesPerParticle = 4;
	const int indicesPerParticle = 6;

	m_vertices.resize (m_maxParticles * verticesPerParticle * SPRITE_FLOATS_PER_VERTEX);
	m_indices.resize (m_maxParticles * indicesPerParticle);
    }
}

CParticle::~CParticle () {
    delete m_pass;

    if (m_vao != 0) {
	glDeleteVertexArrays (1, &m_vao);
    }
    if (m_vbo != 0) {
	glDeleteBuffers (1, &m_vbo);
    }
    if (m_ebo != 0) {
	glDeleteBuffers (1, &m_ebo);
    }

    m_vertices.clear ();
    m_indices.clear ();
}

void CParticle::setup () {
    if (m_initialized) {
	return;
    }

    // Convert origin from screen space (0,0 top-left) to centered space, matching the
    // ortho(-width/2, width/2, -height/2, height/2) projection
    m_lastScreenWidth = getScene ().getCamera ().getWidth ();
    m_lastScreenHeight = getScene ().getCamera ().getHeight ();

    glm::vec3 origin = m_particle.origin->value->getVec3 ();
    origin.x -= m_lastScreenWidth / 2.0f;
    origin.y = m_lastScreenHeight / 2.0f - origin.y;
    m_transformedOrigin = origin;

    if (m_particle.material && m_particle.material->material && !m_particle.material->material->passes.empty ()) {
	auto& firstPass = *m_particle.material->material->passes.begin ();

	// Overbright: brightness multiplier for additive particles
	auto overbrightIt = firstPass->constants.find ("ui_editor_properties_overbright");
	if (overbrightIt != firstPass->constants.end ()) {
	    m_overbright = overbrightIt->second->value->getFloat ();
	}
    }

    // TextureParser computes the spritesheet grid from TEXS frame data (animated textures) or
    // .tex-json metadata (static textures). GIF-style animated textures (separate GL texture per
    // frame) get 0 cols/rows since a 1x1 grid can't hold all frames - no SPRITESHEET mode needed,
    // frame switching happens via texture ID instead.
    if (const auto texture = getTexture ()) {
	m_spritesheetCols = static_cast<int> (texture->getSpritesheetCols ());
	m_spritesheetRows = static_cast<int> (texture->getSpritesheetRows ());
	m_spritesheetFrames = static_cast<int> (texture->getSpritesheetFrames ());
	m_spritesheetDuration = texture->getSpritesheetDuration ();
    }

    setupEmitters ();
    setupInitializers ();
    setupOperators ();
    setupPass ();

    m_controlPoints.resize (8);
    for (const auto& cp : m_particle.controlPoints) {
	if (cp.id >= 0 && cp.id < 8) {
	    m_controlPoints[cp.id].offset = cp.offset;
	    // flags bit 0 = linkMouse
	    m_controlPoints[cp.id].linkMouse = (cp.flags & 1) != 0;
	    m_controlPoints[cp.id].worldSpace = (cp.flags & 2) != 0;

	    if (m_controlPoints[cp.id].linkMouse) {
		m_hasMouseControlPoint = true;
	    }

	    // Mouse-linked CPs get their position from update() instead
	    if (!m_controlPoints[cp.id].linkMouse) {
		if (m_controlPoints[cp.id].worldSpace) {
		    // World space: offset is in screen-centered coords, convert to particle local space
		    m_controlPoints[cp.id].position = cp.offset - m_transformedOrigin;
		} else {
		    // Local space: offset is already relative to particle system center
		    m_controlPoints[cp.id].position = cp.offset;
		}
	    }
	}
    }

    m_initialized = true;
}

void CParticle::render () {
    if (!m_initialized) {
	return;
    }

    const auto& appContext = this->getScene ().getContext ().getApp ().getContext ();
    const auto visibility = appContext.resolveObjectVisibility (this->getId (), this->getObject ().name);
    if (!visibility.value_or (m_particle.visible->value->getBool ())) {
	return;
    }

    syncTransformedOrigin ();

    // stop() drops every particle, and a later play() starts emitting from scratch
    const auto playback = this->getPlayback ();
    if (playback == Playback::Stopped) {
	m_particleCount = 0;
    } else if (m_lastPlayback == Playback::Stopped) {
	m_emitters.clear ();
	setupEmitters ();
    }
    m_lastPlayback = playback;

    const float currentTime = m_hasMouseControlPoint ? g_RealTime : g_Time;

    // Initialize time on first render to avoid a huge dt spike, and skip the update
    // that frame to avoid an initial burst
    if (m_time == 0.0) {
	m_time = currentTime;
	// "starttime" prewarms the system so it starts already populated instead of every
	// particle visibly leaving the emitter at once
	if (!m_prewarmed && m_particle.startTime > 0.0f && playback == Playback::Playing) {
	    m_prewarmed = true;
	    constexpr float step = 1.0f / 30.0f;
	    m_time = currentTime - m_particle.startTime;
	    for (float left = m_particle.startTime; left > 0.0f; left -= step) {
		const float dt = std::min (step, left);
		m_time += dt;
		update (dt);
	    }
	    m_time = currentTime;
	}
	if (m_useRopeRenderer) {
	    renderRope ();
	} else {
	    renderSprites ();
	}
	return;
    }

    float dt = currentTime - static_cast<float> (m_time);
    m_time = currentTime;

    if (dt > 0.0f && playback != Playback::Stopped) {
	// Cap dt to prevent simulation instability across different FPS
	dt = std::min (dt, 0.1f);
	update (dt);
    }

    if (m_particleCount > 0 && m_particle.material) {
	if (m_useRopeRenderer) {
	    renderRope ();
	} else {
	    renderSprites ();
	}
    }
}

bool CParticle::isPlaying () const {
    const auto playback = this->getPlayback ();

    return playback == Playback::Playing || (playback == Playback::Paused && m_particleCount > 0);
}

// scripts can move the system every frame (e.g. an origin that follows the cursor)
void CParticle::syncTransformedOrigin () {
    const float screenWidth = static_cast<float> (getScene ().getWidth ());
    const float screenHeight = static_cast<float> (getScene ().getHeight ());

    glm::vec3 origin = m_particle.origin->value->getVec3 ();
    origin.x -= screenWidth / 2.0f;
    origin.y = screenHeight / 2.0f - origin.y;

    if (origin == m_transformedOrigin && screenWidth == m_lastScreenWidth && screenHeight == m_lastScreenHeight) {
	return;
    }

    m_transformedOrigin = origin;
    m_lastScreenWidth = screenWidth;
    m_lastScreenHeight = screenHeight;

    for (auto& cp : m_controlPoints) {
	if (!cp.linkMouse && cp.worldSpace) {
	    cp.position = cp.offset - m_transformedOrigin;
	}
    }
}

void CParticle::update (float dt) {
    float screenWidth = static_cast<float> (getScene ().getWidth ());
    float screenHeight = static_cast<float> (getScene ().getHeight ());

    const glm::vec2* mousePos = getScene ().getMousePositionNormalized ();
    if (mousePos) {

	for (auto& cp : m_controlPoints) {
	    if (cp.linkMouse) {
		// Convert mouse position from normalized [0,1] to centered screen space
		glm::vec3 position;
		position.x = (mousePos->x * screenWidth) - (screenWidth / 2.0f);
		position.y = (screenHeight / 2.0f) - (mousePos->y * screenHeight);
		position.z = 0.0f;

		position += cp.offset;

		// Subtract transformed origin to keep in particle local space (avoids
		// double transformation by the model matrix)
		cp.position = position - m_transformedOrigin;
	    }
	}
    }

    // pause() stops emission but keeps simulating what is already alive
    if (this->getPlayback () == Playback::Playing) {
	for (auto& emitter : m_emitters) {
	    emitter (m_particles, m_particleCount, dt);
	}
    }

    for (uint32_t i = 0; i < m_particleCount; i++) {
	m_particles[i].age += dt;
    }

    for (auto& op : m_operators) {
	op (m_particles, m_particleCount, m_controlPoints, static_cast<float> (m_time), dt);
    }

    for (uint32_t i = 0; i < m_particleCount; i++) {
	auto& p = m_particles[i];

	if (m_spritesheetFrames > 0) {
	    float lifetimePos = p.getLifetimePos ();
	    float animSpeed = m_particle.sequenceMultiplier > 0.0f ? m_particle.sequenceMultiplier : 1.0f;

	    if (m_particle.animationMode == "randomframe") {
		if (p.frame < 0.0f) {
		    std::mt19937 particleRng (
			static_cast<std::mt19937::result_type> (reinterpret_cast<uintptr_t> (&p))
		    );
		    std::uniform_int_distribution<int> dist (0, m_spritesheetFrames - 1);
		    p.frame = static_cast<float> (dist (particleRng));
		}
	    } else if (m_particle.animationMode == "once") {
		p.frame = std::min (
		    lifetimePos * m_spritesheetFrames * animSpeed, static_cast<float> (m_spritesheetFrames - 1)
		);
	    } else {
		if (m_spritesheetDuration > 0.0f) {
		    float timeInCycle = std::fmod (p.age * animSpeed, m_spritesheetDuration);
		    float cyclePos = timeInCycle / m_spritesheetDuration;
		    p.frame = std::fmod (cyclePos * m_spritesheetFrames, static_cast<float> (m_spritesheetFrames));
		} else {
		    p.frame = std::fmod (
			lifetimePos * m_spritesheetFrames * animSpeed, static_cast<float> (m_spritesheetFrames)
		    );
		}
	    }
	}
    }

    // Order-preserving compaction: particles only die from lifetime expiry (never from
    // size, since size can oscillate), and index 0 must stay the oldest particle
    uint32_t writeIdx = 0;
    for (uint32_t readIdx = 0; readIdx < m_particleCount; readIdx++) {
	if (m_particles[readIdx].isAlive ()) {
	    if (writeIdx != readIdx) {
		m_particles[writeIdx] = m_particles[readIdx];
	    }
	    writeIdx++;
	}
    }
    m_particleCount = writeIdx;
}

const Particle& CParticle::getParticle () const { return m_particle; }

const float& CParticle::getBrightness () const { return m_overbright; }

const float& CParticle::getUserAlpha () const { return m_particle.instanceOverride.alpha->value->getFloat (); }

const float& CParticle::getAlpha () const { return m_particle.instanceOverride.alpha->value->getFloat (); }

const glm::vec3& CParticle::getColor () const {
    static const glm::vec3 defaultColor (1.0f);
    if (m_particle.instanceOverride.color && m_particle.instanceOverride.color->value) {
	return m_particle.instanceOverride.color->value->getVec3 ();
    }
    return defaultColor;
}

const glm::vec4& CParticle::getColor4 () const {
    static const glm::vec4 defaultColor (1.0f);
    if (m_particle.instanceOverride.color && m_particle.instanceOverride.color->value) {
	return m_particle.instanceOverride.color->value->getVec4 ();
    }
    return defaultColor;
}

const glm::vec3& CParticle::getCompositeColor () const { return getColor (); }

// ========== EMITTERS ==========

void CParticle::setupEmitters () {
    for (const auto& emitter : m_particle.emitters) {
	EmitterFunc func;

	if (emitter.name == "boxrandom") {
	    func = createBoxEmitter (emitter);
	} else if (emitter.name == "sphererandom") {
	    func = createSphereEmitter (emitter);
	} else {
	    sLog.out ("Unknown emitter type: ", emitter.name);
	    continue;
	}

	if (func) {
	    m_emitters.push_back (std::move (func));
	}
    }
}

float CParticle::sampleAudio (
    int mode, const glm::vec2& bounds, float exponent, int frequencyStart, int frequencyEnd
) const {
    // same curve as wallpaper64.exe. Modes 1/2/3 pick left/right/averaged channels there, the recorder is mono
    if (mode == 0) {
	return 1.0f;
    }

    int first = std::clamp (frequencyStart, 0, 15);
    int last = std::clamp (frequencyEnd, 0, 15);

    if (last < first) {
	std::swap (first, last);
    }

    const auto& recorder = this->getScene ().getAudioContext ().getRecorder ();
    float peak = 0.0f;

    recorder.lock ();
    for (int i = first; i <= last; i++) {
	peak = std::max (peak, recorder.audio16[i]);
    }
    recorder.unlock ();

    float t = (peak - bounds.x) / (bounds.y - bounds.x);
    // NaN from equal bounds ends up as 0 like the original
    t = t >= 1.0f ? 1.0f : (t >= 0.0f ? t : 0.0f);

    const float response = std::pow (t * t * (3.0f - 2.0f * t), exponent);

    return response >= 1.0f ? 1.0f : (response >= 0.0f ? response : 0.0f);
}

EmitterFunc CParticle::createBoxEmitter (const ParticleEmitter& emitter) {
    float rate = emitter.rate * m_particle.instanceOverride.rate->value->getFloat ();

    glm::vec3 transformedEmitterOrigin = emitter.origin;
    transformedEmitterOrigin.y = -transformedEmitterOrigin.y;

    int controlPointIndex = emitter.controlPoint;
    if (controlPointIndex == -1 && !m_particle.controlPoints.empty ()) {
	const auto& cp0 = m_particle.controlPoints[0];
	if ((cp0.flags & 1) != 0) {
	    controlPointIndex = 0;
	}
    }

    glm::vec3 flippedDirections = emitter.directions;
    flippedDirections.y = -flippedDirections.y;

    bool limitOnePerFrame = (emitter.flags & 2) != 0;
    bool randomPeriodicEmission = (emitter.flags & 4) != 0;

    return
	[this, emitter, transformedEmitterOrigin, controlPointIndex, rate, flippedDirections, limitOnePerFrame,
	 randomPeriodicEmission, emissionTimer = 0.0f, delayTimer = emitter.delay, durationTimer = 0.0f,
	 periodicTimer = 0.0f, periodicDuration = 0.0f, periodicDelay = 0.0f, emitting = false,
	 instantaneousEmitted = false] (std::vector<ParticleInstance>& particles, uint32_t& count, float dt) mutable {
	    if (count >= particles.size ()) {
		return;
	    }

	    if (delayTimer > 0.0f) {
		delayTimer -= dt;
		return;
	    }

	    if (emitter.duration > 0.0f) {
		durationTimer += dt;
		if (durationTimer >= emitter.duration) {
		    return;
		}
	    }

	    if (randomPeriodicEmission) {
		periodicTimer += dt;

		if (!emitting) {
		    if (periodicTimer >= periodicDelay) {
			emitting = true;
			periodicTimer = 0.0f;
			periodicDuration = WallpaperEngine::Maths::randomFloat (
			    m_rng, emitter.minPeriodicDuration, emitter.maxPeriodicDuration
			);
		    } else {
			return;
		    }
		} else {
		    if (periodicTimer >= periodicDuration) {
			emitting = false;
			periodicTimer = 0.0f;
			periodicDelay = WallpaperEngine::Maths::randomFloat (
			    m_rng, emitter.minPeriodicDelay, emitter.maxPeriodicDelay
			);
			return;
		    }
		}
	    }

	    uint32_t toEmit = 0;
	    if (emitter.instantaneous > 0 && !instantaneousEmitted) {
		toEmit = emitter.instantaneous;
		instantaneousEmitted = true;
	    }

	    if (emitter.rate > 0.0f) {
		const float audio = sampleAudio (
		    emitter.audioProcessingMode, emitter.audioProcessingBounds, emitter.audioProcessingExponent,
		    emitter.audioProcessingFrequencyStart, emitter.audioProcessingFrequencyEnd
		);
		emissionTimer += dt * rate * audio;
		uint32_t rateEmit = static_cast<uint32_t> (emissionTimer);
		emissionTimer -= static_cast<float> (rateEmit);
		// limitOnePerFrame (flags bit 1): cap at 1 to prevent rope artifacts
		if (limitOnePerFrame && rateEmit > 1) {
		    rateEmit = 1;
		}
		toEmit += rateEmit;
	    }

	    for (uint32_t i = 0; i < toEmit && count < particles.size (); i++) {
		auto& p = particles[count];

		glm::vec3 spawnOrigin = transformedEmitterOrigin;
		if (controlPointIndex >= 0 && controlPointIndex < static_cast<int> (m_controlPoints.size ())) {
		    spawnOrigin += m_controlPoints[controlPointIndex].position;
		}

		// Random position within the box volume (hollow box if distanceMin > 0)
		glm::vec3 randomPos;
		for (int axis = 0; axis < 3; axis++) {
		    float minDist = emitter.distanceMin[axis];
		    float maxDist = emitter.distanceMax[axis];
		    float dist = WallpaperEngine::Maths::randomFloat (m_rng, minDist, maxDist);
		    // Randomly flip sign to center the distribution
		    if (WallpaperEngine::Maths::randomFloat (m_rng, 0.0f, 1.0f) < 0.5f) {
			dist = -dist;
		    }
		    randomPos[axis] = dist;
		}
		randomPos *= flippedDirections;

		p.position = spawnOrigin + randomPos;

		// Emitter does not set velocity - initializers handle that
		p.velocity = glm::vec3 (0.0f);
		p.acceleration = glm::vec3 (0.0f);
		p.rotation = glm::vec3 (0.0f);
		p.angularVelocity = glm::vec3 (0.0f);
		p.angularAcceleration = glm::vec3 (0.0f);

		p.color = glm::vec3 (1.0f) * m_particle.instanceOverride.colorn->value->getVec3 ();
		p.alpha = 1.0f * m_particle.instanceOverride.alpha->value->getFloat ();
		p.size = 20.0f * m_particle.instanceOverride.size->value->getFloat ();
		p.lifetime = 1.0f * m_particle.instanceOverride.lifetime->value->getFloat ();
		p.age = 0.0f;
		p.alive = true;
		p.frame = -1.0f;

		p.initial.color = p.color;
		p.initial.alpha = p.alpha;
		p.initial.size = p.size;
		p.initial.lifetime = p.lifetime;

		// Reset oscillator state for reused particles
		p.oscillateAlpha = {};
		p.oscillateSize = {};
		p.oscillatePosition = {};

		for (auto& init : m_initializers) {
		    init (p);
		}

		count++;
	    }
	};
}

EmitterFunc CParticle::createSphereEmitter (const ParticleEmitter& emitter) {
    float rate = emitter.rate * m_particle.instanceOverride.rate->value->getFloat ();
    float lifetime = 1.0f * m_particle.instanceOverride.lifetime->value->getFloat ();

    // Convert emitter origin from screen space (Y down) to centered space (Y up)
    glm::vec3 transformedEmitterOrigin = emitter.origin;
    transformedEmitterOrigin.y = -transformedEmitterOrigin.y;

    int controlPointIndex = emitter.controlPoint;

    // Auto-detect control point 0 if not specified and CP0 has linkMouse
    if (controlPointIndex == -1 && !m_particle.controlPoints.empty ()) {
	const auto& cp0 = m_particle.controlPoints[0];
	if ((cp0.flags & 1) != 0) { // bit 0 = linkMouse
	    controlPointIndex = 0;
	}
    }

    bool limitOnePerFrame = (emitter.flags & 2) != 0;

    return [this, emitter, transformedEmitterOrigin, controlPointIndex, rate, lifetime, limitOnePerFrame,
	    emissionTimer = 0.0f,
	    remaining
	    = emitter.instantaneous] (std::vector<ParticleInstance>& particles, uint32_t& count, float dt) mutable {
	if (count >= particles.size ()) {
	    return;
	}

	const float audio = sampleAudio (
	    emitter.audioProcessingMode, emitter.audioProcessingBounds, emitter.audioProcessingExponent,
	    emitter.audioProcessingFrequencyStart, emitter.audioProcessingFrequencyEnd
	);
	emissionTimer += dt * rate * audio;
	uint32_t toEmit = static_cast<uint32_t> (emissionTimer);
	emissionTimer -= static_cast<float> (toEmit);
	// limitOnePerFrame (flags bit 1): cap at 1 to prevent rope artifacts
	if (limitOnePerFrame && toEmit > 1) {
	    toEmit = 1;
	}

	if (remaining > 0) {
	    toEmit = remaining;
	    remaining = 0;
	}

	for (uint32_t i = 0; i < toEmit && count < particles.size (); i++) {
	    auto& p = particles[count];

	    glm::vec3 spawnOrigin = transformedEmitterOrigin;
	    if (controlPointIndex >= 0 && controlPointIndex < static_cast<int> (m_controlPoints.size ())) {
		spawnOrigin += m_controlPoints[controlPointIndex].position;
	    }

	    glm::vec3 randomPos;

	    // flags & 4 == 0: orthographic particles use a 2D disk distribution in X/Y
	    // flags & 4 != 0: perspective particles use a 3D spherical shell distribution
	    if ((m_particle.flags & 4) == 0) {
		float angle = WallpaperEngine::Maths::randomFloat (m_rng, 0.0f, glm::two_pi<float> ());
		float minRadius = emitter.distanceMin.x;
		float maxRadius = emitter.distanceMax.x;

		// Use sqrt for uniform area distribution in annulus
		float minRadiusSq = minRadius * minRadius;
		float maxRadiusSq = maxRadius * maxRadius;
		float radiusXY = std::sqrt (WallpaperEngine::Maths::randomFloat (m_rng, minRadiusSq, maxRadiusSq));

		randomPos = glm::vec3 (
		    radiusXY * std::cos (angle), radiusXY * std::sin (angle),
		    WallpaperEngine::Maths::randomFloat (m_rng, -maxRadius, maxRadius)
		);

		randomPos *= emitter.directions;
	    } else {
		float theta = WallpaperEngine::Maths::randomFloat (m_rng, 0.0f, glm::two_pi<float> ());
		float cosTheta = WallpaperEngine::Maths::randomFloat (m_rng, -1.0f, 1.0f);
		float sinTheta = std::sqrt (1.0f - cosTheta * cosTheta);

		randomPos = glm::vec3 (sinTheta * std::cos (theta), sinTheta * std::sin (theta), cosTheta);

		// Use cubic root for uniform volume distribution
		float minRadius = emitter.distanceMin.x;
		float maxRadius = emitter.distanceMax.x;
		float minRadiusCubed = minRadius * minRadius * minRadius;
		float maxRadiusCubed = maxRadius * maxRadius * maxRadius;
		float radius = std::cbrt (WallpaperEngine::Maths::randomFloat (m_rng, minRadiusCubed, maxRadiusCubed));

		randomPos *= radius;
		randomPos *= emitter.directions;
	    }

	    // sign property forces per-axis polarity: 0 = both, 1 = positive only, -1 = negative only
	    for (int i = 0; i < 3; i++) {
		if (emitter.sign[i] == 1) {
		    randomPos[i] = std::abs (randomPos[i]);
		} else if (emitter.sign[i] == -1) {
		    randomPos[i] = -std::abs (randomPos[i]);
		}
	    }
	    p.position = spawnOrigin + randomPos;

	    // Set velocity only if emitter specifies speed (otherwise use initializers)
	    if (emitter.speedMax > 0.0f || emitter.speedMin != 0.0f) {
		// Velocity pointing outward from ellipsoid (randomPos already includes directions scaling)
		glm::vec3 direction
		    = glm::length (randomPos) > 0.0f ? glm::normalize (randomPos) : glm::vec3 (0.0f, 1.0f, 0.0f);
		float speed = WallpaperEngine::Maths::randomFloat (m_rng, emitter.speedMin, emitter.speedMax);
		p.velocity = direction * speed;
	    } else {
		p.velocity = glm::vec3 (0.0f);
	    }

	    p.acceleration = glm::vec3 (0.0f);
	    p.rotation = glm::vec3 (0.0f);
	    p.angularVelocity = glm::vec3 (0.0f);
	    p.angularAcceleration = glm::vec3 (0.0f);

	    p.color = glm::vec3 (1.0f) * m_particle.instanceOverride.colorn->value->getVec3 ();
	    p.alpha = 1.0f * m_particle.instanceOverride.alpha->value->getFloat ();
	    p.size = 20.0f * m_particle.instanceOverride.size->value->getFloat ();
	    p.lifetime = lifetime;
	    p.age = 0.0f;
	    p.alive = true;
	    p.frame = -1.0f;

	    p.initial.color = p.color;
	    p.initial.alpha = p.alpha;
	    p.initial.size = p.size;
	    p.initial.lifetime = p.lifetime;

	    // Reset oscillator state for reused particles
	    p.oscillateAlpha = {};
	    p.oscillateSize = {};
	    p.oscillatePosition = {};

	    for (auto& init : m_initializers) {
		init (p);
	    }

	    count++;
	}
    };
}

// ========== INITIALIZERS ==========

void CParticle::setupInitializers () {
    for (const auto& initializer : m_particle.initializers) {
	if (!initializer) {
	    continue;
	}

	InitializerFunc func;

	if (initializer->is<ColorRandomInitializer> ()) {
	    func = createColorRandomInitializer (*initializer->as<ColorRandomInitializer> ());
	} else if (initializer->is<SizeRandomInitializer> ()) {
	    func = createSizeRandomInitializer (*initializer->as<SizeRandomInitializer> ());
	} else if (initializer->is<AlphaRandomInitializer> ()) {
	    func = createAlphaRandomInitializer (*initializer->as<AlphaRandomInitializer> ());
	} else if (initializer->is<LifetimeRandomInitializer> ()) {
	    const auto& lifeInit = *initializer->as<LifetimeRandomInitializer> ();
	    m_uniformLifetimes = (lifeInit.min->value->getFloat () == lifeInit.max->value->getFloat ());
	    func = createLifetimeRandomInitializer (lifeInit);
	} else if (initializer->is<VelocityRandomInitializer> ()) {
	    func = createVelocityRandomInitializer (*initializer->as<VelocityRandomInitializer> ());
	} else if (initializer->is<RotationRandomInitializer> ()) {
	    func = createRotationRandomInitializer (*initializer->as<RotationRandomInitializer> ());
	} else if (initializer->is<AngularVelocityRandomInitializer> ()) {
	    func = createAngularVelocityRandomInitializer (*initializer->as<AngularVelocityRandomInitializer> ());
	} else if (initializer->is<TurbulentVelocityRandomInitializer> ()) {
	    func = createTurbulentVelocityRandomInitializer (*initializer->as<TurbulentVelocityRandomInitializer> ());
	} else if (initializer->is<MapSequenceAroundControlPointInitializer> ()) {
	    func = createMapSequenceAroundControlPointInitializer (
		*initializer->as<MapSequenceAroundControlPointInitializer> ()
	    );
	} else {
	    sLog.out ("Unknown initializer type");
	}

	if (func) {
	    m_initializers.push_back (std::move (func));
	}
    }
}

InitializerFunc CParticle::createColorRandomInitializer (const ColorRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* colorOverride = m_particle.instanceOverride.colorn->value.get ();

    return [this, minValue, maxValue, colorOverride] (ParticleInstance& p) {
	p.color = WallpaperEngine::Maths::randomVec3 (m_rng, minValue->getVec3 (), maxValue->getVec3 ())
	    * colorOverride->getVec3 ();
	p.initial.color = p.color;
    };
}

InitializerFunc CParticle::createSizeRandomInitializer (const SizeRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* exponentValue = init.exponent->value.get ();
    DynamicValue* sizeOverride = m_particle.instanceOverride.size->value.get ();

    return [this, minValue, maxValue, exponentValue, sizeOverride] (ParticleInstance& p) {
	float t = WallpaperEngine::Maths::randomFloat (m_rng, 0.0f, 1.0f);
	float exponent = exponentValue->getFloat ();
	float min = minValue->getFloat ();
	float max = maxValue->getFloat ();

	// Apply exponent for non-linear distribution
	float adjustedT = std::pow (t, exponent);
	p.size = (min + adjustedT * (max - min)) * sizeOverride->getFloat () / 2.0f;
	p.initial.size = p.size;
    };
}

InitializerFunc CParticle::createAlphaRandomInitializer (const AlphaRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* alphaOverride = m_particle.instanceOverride.alpha->value.get ();

    return [this, minValue, maxValue, alphaOverride] (ParticleInstance& p) {
	p.alpha = WallpaperEngine::Maths::randomFloat (m_rng, minValue->getFloat (), maxValue->getFloat ())
	    * alphaOverride->getFloat ();
	p.initial.alpha = p.alpha;
    };
}

InitializerFunc CParticle::createLifetimeRandomInitializer (const LifetimeRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* lifetimeOverride = m_particle.instanceOverride.lifetime->value.get ();

    return [this, minValue, maxValue, lifetimeOverride] (ParticleInstance& p) {
	p.lifetime = WallpaperEngine::Maths::randomFloat (m_rng, minValue->getFloat (), maxValue->getFloat ())
	    * lifetimeOverride->getFloat ();
	p.initial.lifetime = p.lifetime;
    };
}

InitializerFunc CParticle::createVelocityRandomInitializer (const VelocityRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [this, minValue, maxValue, speedOverride] (ParticleInstance& p) {
	glm::vec3 vel = WallpaperEngine::Maths::randomVec3 (m_rng, minValue->getVec3 (), maxValue->getVec3 ())
	    * speedOverride->getFloat ();
	vel.y = -vel.y;
	p.velocity += vel;
    };
}

InitializerFunc CParticle::createRotationRandomInitializer (const RotationRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [this, minValue, maxValue, speedOverride] (ParticleInstance& p) {
	p.rotation = WallpaperEngine::Maths::randomVec3 (m_rng, minValue->getVec3 (), maxValue->getVec3 ())
	    * speedOverride->getFloat ();
    };
}

InitializerFunc CParticle::createAngularVelocityRandomInitializer (const AngularVelocityRandomInitializer& init) {
    DynamicValue* minValue = init.min->value.get ();
    DynamicValue* maxValue = init.max->value.get ();
    DynamicValue* exponentValue = init.exponent->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [this, minValue, maxValue, exponentValue, speedOverride] (ParticleInstance& p) {
	glm::vec3 minVec = minValue->getVec3 ();
	glm::vec3 maxVec = maxValue->getVec3 ();
	float exponent = exponentValue->getFloat ();

	// exponent = 1: uniform; exponent -> 0: bias towards max; exponent >= 2: bias towards min
	glm::vec3 result;
	for (int i = 0; i < 3; i++) {
	    float t = WallpaperEngine::Maths::randomFloat (m_rng, 0.0f, 1.0f);
	    t = std::pow (t, exponent);
	    result[i] = minVec[i] + t * (maxVec[i] - minVec[i]);
	}

	p.angularVelocity = result * speedOverride->getFloat ();
    };
}

InitializerFunc CParticle::createTurbulentVelocityRandomInitializer (const TurbulentVelocityRandomInitializer& init) {
    DynamicValue* speedMin = init.speedMin->value.get ();
    DynamicValue* speedMax = init.speedMax->value.get ();
    DynamicValue* offsetVal = init.offset->value.get ();
    DynamicValue* scaleVal = init.scale->value.get ();
    DynamicValue* forwardVal = init.forward->value.get ();
    DynamicValue* timeScaleVal = init.timeScale->value.get ();
    DynamicValue* phaseMinVal = init.phaseMin->value.get ();
    DynamicValue* phaseMaxVal = init.phaseMax->value.get ();
    DynamicValue* rightVal = init.right->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [this, speedMin, speedMax, offsetVal, scaleVal, forwardVal, timeScaleVal, phaseMinVal, phaseMaxVal, rightVal,
	    speedOverride] (ParticleInstance& p) {
	glm::vec3 forward = forwardVal->getVec3 ();
	glm::vec3 right = rightVal->getVec3 ();
	// Y-flip for coordinate system conversion
	forward.y = -forward.y;
	right.y = -right.y;

	if (glm::length (forward) > 0.0001f) {
	    forward = glm::normalize (forward);
	} else {
	    // Default forward direction when not specified (up in centered space)
	    forward = glm::vec3 (0.0f, 1.0f, 0.0f);
	}
	if (glm::length (right) > 0.0001f) {
	    right = glm::normalize (right);
	} else {
	    right = glm::vec3 (1.0f, 0.0f, 0.0f);
	}

	float speed = WallpaperEngine::Maths::randomFloat (m_rng, speedMin->getFloat (), speedMax->getFloat ());
	float scale = scaleVal->getFloat ();
	float offset = offsetVal->getFloat ();
	float timeScale = timeScaleVal->getFloat ();
	float phaseMin = phaseMinVal->getFloat ();
	float phaseMax = phaseMaxVal->getFloat ();

	// Sample noise at position + time offset: timescale shifts the field over time so
	// particles spawned at different times drift differently (evolving vapor stream);
	// the position term gives spatial coherence between nearby particles.
	glm::vec3 noisePos = p.position * 0.1f;
	noisePos += glm::vec3 (static_cast<float> (m_time) * timeScale);

	// Phase adds per-particle randomization to noise position
	float phase = WallpaperEngine::Maths::randomFloat (m_rng, phaseMin, phaseMax);
	glm::vec3 samplePos = noisePos + glm::vec3 (phase, phase * 0.7f, phase * 1.3f);

	glm::vec3 result = curlNoise (samplePos);
	float len = glm::length (result);
	if (len < 0.0001f) {
	    result = forward;
	} else {
	    result = result / len;
	}

	// Scale limits how far direction can deviate from forward
	if (scale < 2.0f) {
	    float cosAngle = glm::dot (result, forward);
	    float angle = std::acos (glm::clamp (cosAngle, -1.0f, 1.0f)) / glm::pi<float> ();
	    float maxAngle = scale / 2.0f;

	    if (angle > maxAngle && maxAngle > 0.0001f) {
		glm::vec3 axis = glm::cross (result, forward);
		float axisLen = glm::length (axis);
		if (axisLen > 0.0001f) {
		    axis = axis / axisLen;
		    float rotAngle = (angle - maxAngle) * glm::pi<float> ();
		    glm::mat3 rot = glm::mat3 (glm::rotate (glm::mat4 (1.0f), rotAngle, axis));
		    result = rot * result;
		}
	    }
	}

	// Offset rotates result around right axis (tilts up/down)
	if (std::abs (offset) > 0.0001f) {
	    glm::mat3 rot = glm::mat3 (glm::rotate (glm::mat4 (1.0f), -offset, right));
	    result = rot * result;
	}

	// 2D/orthographic particles (flags & 4 == 0): project onto XY. curlNoise is 3D but
	// z-drift is meaningless here and makes rope segments diverge in depth.
	if ((m_particle.flags & 4) == 0) {
	    result.z = 0.0f;
	    float len2d = glm::length (result);
	    if (len2d > 0.0001f) {
		result /= len2d;
	    }
	}

	glm::vec3 finalVel = result * speed * speedOverride->getFloat ();

	p.velocity += finalVel;
    };
}

InitializerFunc
CParticle::createMapSequenceAroundControlPointInitializer (const MapSequenceAroundControlPointInitializer& init) {
    DynamicValue* controlPointValue = init.controlPoint->value.get ();
    DynamicValue* countValue = init.count->value.get ();
    DynamicValue* speedMinValue = init.speedMin->value.get ();
    DynamicValue* speedMaxValue = init.speedMax->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    // Sequence counter is shared (closure state) across all particles spawned by this
    // initializer, giving each one a distinct angle around the circle
    int sequenceIndex = 0;

    return [this, controlPointValue, countValue, speedMinValue, speedMaxValue, sequenceIndex,
	    speedOverride] (ParticleInstance& p) mutable {
	int controlPoint = static_cast<int> (controlPointValue->getFloat ());
	int count = static_cast<int> (countValue->getFloat ());
	if (count < 1) {
	    count = 1;
	}

	float angle = (static_cast<float> (sequenceIndex) / static_cast<float> (count)) * glm::two_pi<float> ();
	sequenceIndex = (sequenceIndex + 1) % count;

	glm::vec3 centerPos = glm::vec3 (0.0f);
	if (controlPoint >= 0 && controlPoint < static_cast<int> (m_controlPoints.size ())) {
	    centerPos = m_controlPoints[controlPoint].position;
	}

	p.position = centerPos;

	glm::vec3 speedMin = speedMinValue->getVec3 ();
	glm::vec3 speedMax = speedMaxValue->getVec3 ();
	glm::vec3 speed = WallpaperEngine::Maths::randomVec3 (m_rng, speedMin, speedMax);

	// Flip Y before rotation to convert to centered space
	speed.y = -speed.y;

	// Rotating by the sequence angle gives the outward radial/circular pattern
	glm::mat3 rotationMatrix = glm::mat3 (
	    std::cos (angle), -std::sin (angle), 0.0f, std::sin (angle), std::cos (angle), 0.0f, 0.0f, 0.0f, 1.0f
	);
	glm::vec3 rotatedSpeed = rotationMatrix * speed * speedOverride->getFloat ();

	p.velocity = rotatedSpeed;
    };
}

// ========== OPERATORS ==========

void CParticle::setupOperators () {
    for (const auto& op : m_particle.operators) {
	if (!op) {
	    continue;
	}

	OperatorFunc func;

	if (op->is<MovementOperator> ()) {
	    func = createMovementOperator (*op->as<MovementOperator> ());
	} else if (op->is<AngularMovementOperator> ()) {
	    func = createAngularMovementOperator (*op->as<AngularMovementOperator> ());
	} else if (op->is<AlphaFadeOperator> ()) {
	    func = createAlphaFadeOperator (*op->as<AlphaFadeOperator> ());
	} else if (op->is<SizeChangeOperator> ()) {
	    func = createSizeChangeOperator (*op->as<SizeChangeOperator> ());
	} else if (op->is<AlphaChangeOperator> ()) {
	    func = createAlphaChangeOperator (*op->as<AlphaChangeOperator> ());
	} else if (op->is<ColorChangeOperator> ()) {
	    func = createColorChangeOperator (*op->as<ColorChangeOperator> ());
	} else if (op->is<TurbulenceOperator> ()) {
	    func = createTurbulenceOperator (*op->as<TurbulenceOperator> ());
	} else if (op->is<VortexOperator> ()) {
	    func = createVortexOperator (*op->as<VortexOperator> ());
	} else if (op->is<ControlPointAttractOperator> ()) {
	    func = createControlPointAttractOperator (*op->as<ControlPointAttractOperator> ());
	} else if (op->is<OscillateAlphaOperator> ()) {
	    func = createOscillateAlphaOperator (*op->as<OscillateAlphaOperator> ());
	} else if (op->is<OscillateSizeOperator> ()) {
	    func = createOscillateSizeOperator (*op->as<OscillateSizeOperator> ());
	} else if (op->is<OscillatePositionOperator> ()) {
	    func = createOscillatePositionOperator (*op->as<OscillatePositionOperator> ());
	} else {
	    sLog.out ("Unknown operator type");
	}

	if (func) {
	    m_operators.push_back (std::move (func));
	}
    }
}

OperatorFunc CParticle::createMovementOperator (const MovementOperator& op) {
    DynamicValue* dragValue = op.drag->value.get ();
    DynamicValue* gravityValue = op.gravity->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [dragValue, gravityValue, speedOverride] (
	       std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float,
	       float dt
	   ) {
	float speed = speedOverride->getFloat ();
	float drag = dragValue->getFloat ();
	glm::vec3 gravity = gravityValue->getVec3 ();
	// Flip gravity Y for centered space
	gravity.y = -gravity.y;

	for (uint32_t i = 0; i < count; i++) {
	    auto& p = particles[i];
	    if (!p.alive) {
		continue;
	    }

	    // Integrate position from current velocity (already speed-scaled) before
	    // updating velocity for next frame
	    p.position += p.velocity * dt;

	    p.velocity += gravity * dt * speed;

	    // Drag decay, clamped so drag*dt > 1.0 can't reverse velocity
	    float dragFactor = 1.0f - (drag * dt);
	    if (dragFactor < 0.0f) {
		dragFactor = 0.0f;
	    }
	    p.velocity *= dragFactor;
	}
    };
}

OperatorFunc CParticle::createAngularMovementOperator (const AngularMovementOperator& op) {
    DynamicValue* dragValue = op.drag->value.get ();
    DynamicValue* forceValue = op.force->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [dragValue, forceValue, speedOverride] (
	       std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float,
	       float dt
	   ) {
	float drag = dragValue->getFloat ();
	float speed = speedOverride->getFloat ();
	glm::vec3 force = forceValue->getVec3 ();

	for (uint32_t i = 0; i < count; i++) {
	    auto& p = particles[i];
	    if (!p.alive) {
		continue;
	    }

	    p.rotation += p.angularVelocity * dt * speed;

	    p.angularVelocity += force * dt * speed;

	    // Positive drag slows down, negative speeds up; clamped so drag*dt > 1.0 can't reverse it
	    float dragFactor = 1.0f - (drag * dt);
	    if (dragFactor < 0.0f) {
		dragFactor = 0.0f;
	    }
	    p.angularVelocity *= dragFactor;

	    // Wrap rotation to prevent floating-point precision issues
	    const float pi = glm::pi<float> ();
	    const float two_pi = glm::two_pi<float> ();
	    for (int j = 0; j < 3; j++) {
		while (p.rotation[j] > pi) {
		    p.rotation[j] -= two_pi;
		}
		while (p.rotation[j] < -pi) {
		    p.rotation[j] += two_pi;
		}
	    }
	}
    };
}

OperatorFunc CParticle::createAlphaFadeOperator (const AlphaFadeOperator& op) {
    DynamicValue* fadeInTimeValue = op.fadeInTime->value.get ();
    DynamicValue* fadeOutTimeValue = op.fadeOutTime->value.get ();

    return
	[fadeInTimeValue, fadeOutTimeValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float fadeInTime = fadeInTimeValue->getFloat ();
	    float fadeOutTime = fadeOutTimeValue->getFloat ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];
		if (!p.alive) {
		    continue;
		}

		float life = p.getLifetimePos ();

		if (life <= fadeInTime) {
		    float fade = WallpaperEngine::Maths::fadeValue (life, 0.0f, fadeInTime, 0.0f, 1.0f);
		    p.alpha = p.initial.alpha * fade;
		} else if (life > fadeOutTime) {
		    float fade = 1.0f - WallpaperEngine::Maths::fadeValue (life, fadeOutTime, 1.0f, 0.0f, 1.0f);
		    p.alpha = p.initial.alpha * fade;
		} else {
		    p.alpha = p.initial.alpha;
		}

		// Update oscillator base so oscillateAlpha combines properly
		p.oscillateAlpha.base = p.alpha;
	    }
	};
}

OperatorFunc CParticle::createSizeChangeOperator (const SizeChangeOperator& op) {
    DynamicValue* startTimeValue = op.startTime->value.get ();
    DynamicValue* endTimeValue = op.endTime->value.get ();
    DynamicValue* startValueValue = op.startValue->value.get ();
    DynamicValue* endValueValue = op.endValue->value.get ();

    return
	[startTimeValue, endTimeValue, startValueValue, endValueValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float startTime = startTimeValue->getFloat ();
	    float endTime = endTimeValue->getFloat ();
	    float startValue = startValueValue->getFloat ();
	    float endValue = endValueValue->getFloat ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];
		if (!p.alive) {
		    continue;
		}

		float life = p.getLifetimePos ();
		float multiplier = WallpaperEngine::Maths::fadeValue (life, startTime, endTime, startValue, endValue);
		p.size = p.initial.size * multiplier;

		// Update oscillator base so oscillateSize combines properly
		p.oscillateSize.base = p.size;
	    }
	};
}

OperatorFunc CParticle::createAlphaChangeOperator (const AlphaChangeOperator& op) {
    DynamicValue* startTimeValue = op.startTime->value.get ();
    DynamicValue* endTimeValue = op.endTime->value.get ();
    DynamicValue* startValueValue = op.startValue->value.get ();
    DynamicValue* endValueValue = op.endValue->value.get ();

    return
	[startTimeValue, endTimeValue, startValueValue, endValueValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float startTime = startTimeValue->getFloat ();
	    float endTime = endTimeValue->getFloat ();
	    float startValue = startValueValue->getFloat ();
	    float endValue = endValueValue->getFloat ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];
		if (!p.alive) {
		    continue;
		}

		float life = p.getLifetimePos ();
		float multiplier = WallpaperEngine::Maths::fadeValue (life, startTime, endTime, startValue, endValue);
		p.alpha = p.initial.alpha * multiplier;

		// Update oscillator base so oscillateAlpha combines properly
		p.oscillateAlpha.base = p.alpha;
	    }
	};
}

OperatorFunc CParticle::createColorChangeOperator (const ColorChangeOperator& op) {
    DynamicValue* startTimeValue = op.startTime->value.get ();
    DynamicValue* endTimeValue = op.endTime->value.get ();
    DynamicValue* startValueValue = op.startValue->value.get ();
    DynamicValue* endValueValue = op.endValue->value.get ();

    return
	[startTimeValue, endTimeValue, startValueValue, endValueValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float startTime = startTimeValue->getFloat ();
	    float endTime = endTimeValue->getFloat ();
	    glm::vec3 startValue = startValueValue->getVec3 ();
	    glm::vec3 endValue = endValueValue->getVec3 ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];
		if (!p.alive) {
		    continue;
		}

		float life = p.getLifetimePos ();

		glm::vec3 color;
		color.r = WallpaperEngine::Maths::fadeValue (life, startTime, endTime, startValue.r, endValue.r);
		color.g = WallpaperEngine::Maths::fadeValue (life, startTime, endTime, startValue.g, endValue.g);
		color.b = WallpaperEngine::Maths::fadeValue (life, startTime, endTime, startValue.b, endValue.b);

		p.color = p.initial.color * color;
	    }
	};
}

OperatorFunc CParticle::createTurbulenceOperator (const TurbulenceOperator& op) {
    DynamicValue* scaleValue = op.scale->value.get ();
    DynamicValue* speedMinValue = op.speedMin->value.get ();
    DynamicValue* speedMaxValue = op.speedMax->value.get ();
    DynamicValue* timeScaleValue = op.timeScale->value.get ();
    DynamicValue* maskValue = op.mask->value.get ();
    DynamicValue* phaseMinValue = op.phaseMin->value.get ();
    DynamicValue* phaseMaxValue = op.phaseMax->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();
    DynamicValue* audioModeValue = op.audioProcessingMode->value.get ();
    DynamicValue* audioBoundsValue = op.audioProcessingBounds->value.get ();
    DynamicValue* audioExponentValue = op.audioProcessingExponent->value.get ();
    DynamicValue* audioStartValue = op.audioProcessingFrequencyStart->value.get ();
    DynamicValue* audioEndValue = op.audioProcessingFrequencyEnd->value.get ();

    // Phase and speed are randomized once per operator instance, not per particle
    const float phase
	= WallpaperEngine::Maths::randomFloat (m_rng, phaseMinValue->getFloat (), phaseMaxValue->getFloat ());
    const float turbSpeed
	= WallpaperEngine::Maths::randomFloat (m_rng, speedMinValue->getFloat (), speedMaxValue->getFloat ());

    return [this, scaleValue, timeScaleValue, maskValue, speedOverride, audioModeValue, audioBoundsValue,
	    audioExponentValue, audioStartValue, audioEndValue, phase, baseTurbSpeed = turbSpeed] (
	       std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&,
	       float currentTime, float dt
	   ) {
	const float noiseScale = scaleValue->getFloat () * 2.0f;
	const float timeScale = timeScaleValue->getFloat ();
	const glm::vec3 mask = maskValue->getVec3 ();
	const float speed = speedOverride->getFloat ();
	const float audio = sampleAudio (
	    audioModeValue->getInt (), audioBoundsValue->getVec2 (), audioExponentValue->getFloat (),
	    audioStartValue->getInt (), audioEndValue->getInt ()
	);
	const float turbSpeed = baseTurbSpeed * audio;

	if (turbSpeed <= 0.0001f) {
	    return;
	}

	for (size_t i = 0; i < count; ++i) {
	    ParticleInstance& p = particles[i];
	    if (!p.alive) {
		continue;
	    }

	    glm::vec3 noisePos = p.position;
	    noisePos.x += phase + timeScale * currentTime;
	    noisePos *= noiseScale;

	    glm::vec3 curlDir = curlNoise (noisePos);
	    const float len = glm::length (curlDir);
	    if (len > 0.0001f) {
		curlDir = (curlDir / len) * turbSpeed;
	    }

	    curlDir *= mask;
	    p.velocity += curlDir * dt * speed;
	}
    };
}

OperatorFunc CParticle::createVortexOperator (const VortexOperator& op) {
    int controlPoint = op.controlPoint;
    int flags = op.flags;
    DynamicValue* axisValue = op.axis->value.get ();
    DynamicValue* offsetValue = op.offset->value.get ();
    DynamicValue* distanceInnerValue = op.distanceInner->value.get ();
    DynamicValue* distanceOuterValue = op.distanceOuter->value.get ();
    DynamicValue* speedInnerValue = op.speedInner->value.get ();
    DynamicValue* speedOuterValue = op.speedOuter->value.get ();
    DynamicValue* centerForceValue = op.centerForce->value.get ();
    DynamicValue* ringRadiusValue = op.ringRadius->value.get ();
    DynamicValue* ringWidthValue = op.ringWidth->value.get ();
    DynamicValue* ringPullDistanceValue = op.ringPullDistance->value.get ();
    DynamicValue* ringPullForceValue = op.ringPullForce->value.get ();
    DynamicValue* audioModeValue = op.audioProcessingMode->value.get ();
    DynamicValue* audioBoundsValue = op.audioProcessingBounds->value.get ();
    DynamicValue* audioExponentValue = op.audioProcessingExponent->value.get ();
    DynamicValue* audioStartValue = op.audioProcessingFrequencyStart->value.get ();
    DynamicValue* audioEndValue = op.audioProcessingFrequencyEnd->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    bool infiniteAxis = (flags & 1) != 0;
    bool maintainDistance = (flags & 2) != 0;
    bool ringShape = (flags & 4) != 0;

    return [controlPoint, axisValue, offsetValue, distanceInnerValue, distanceOuterValue, speedInnerValue,
	    speedOuterValue, centerForceValue, ringRadiusValue, ringWidthValue, ringPullDistanceValue,
	    ringPullForceValue, audioModeValue, audioBoundsValue, audioExponentValue, audioStartValue, audioEndValue,
	    infiniteAxis, maintainDistance, ringShape, speedOverride, this] (
	       std::vector<ParticleInstance>& particles, uint32_t count,
	       const std::vector<ControlPointData>& controlPoints, float, float dt
	   ) {
	const float audioResponse = sampleAudio (
	    audioModeValue->getInt (), audioBoundsValue->getVec2 (), audioExponentValue->getFloat (),
	    audioStartValue->getInt (), audioEndValue->getInt ()
	);

	if (audioResponse <= 0.0f) {
	    return;
	}

	glm::vec3 axis = axisValue->getVec3 ();
	glm::vec3 offset = offsetValue->getVec3 ();
	float distanceInner = distanceInnerValue->getFloat ();
	float distanceOuter = distanceOuterValue->getFloat ();
	float speedInner = speedInnerValue->getFloat ();
	float speedOuter = speedOuterValue->getFloat ();
	float centerForce = centerForceValue->getFloat ();
	float ringRadius = ringRadiusValue->getFloat ();
	float ringWidth = ringWidthValue->getFloat ();
	float ringPullDistance = ringPullDistanceValue->getFloat ();
	float ringPullForce = ringPullForceValue->getFloat ();

	speedInner *= audioResponse;
	speedOuter *= audioResponse;

	glm::vec3 center = glm::vec3 (0.0f);
	if (controlPoint >= 0 && controlPoint < static_cast<int> (controlPoints.size ())) {
	    center = controlPoints[controlPoint].position + offset;
	} else {
	    center = offset;
	}

	if (glm::length (axis) > 0.0f) {
	    axis = glm::normalize (axis);
	} else {
	    axis = glm::vec3 (0.0f, 0.0f, 1.0f);
	}

	for (uint32_t i = 0; i < count; i++) {
	    auto& p = particles[i];
	    if (!p.alive) {
		continue;
	    }

	    glm::vec3 toParticle = p.position - center;

	    // infiniteAxis: project onto the plane perpendicular to axis (cylinder shape);
	    // otherwise use full 3D distance (sphere shape)
	    float axialDistance = 0.0f;
	    glm::vec3 radialVector = toParticle;
	    if (infiniteAxis) {
		axialDistance = glm::dot (toParticle, axis);
		radialVector = toParticle - axis * axialDistance;
	    }

	    float distance = glm::length (radialVector);

	    glm::vec3 tangent = glm::cross (axis, radialVector);
	    if (glm::length (tangent) > 0.001f) {
		tangent = glm::normalize (tangent);
	    } else {
		continue; // particle is on the axis
	    }

	    float speed = 0.0f;
	    glm::vec3 radialForce = glm::vec3 (0.0f);

	    if (ringShape) {
		// Ring mode: hollow center with ring-shaped influence zone
		float ringInner = ringRadius - ringWidth * 0.5f;
		float ringOuter = ringRadius + ringWidth * 0.5f;

		if (distance < ringInner) {
		    // Inside the ring's hollow center - no spin, but may be pulled outward
		    speed = 0.0f;
		} else if (distance <= ringOuter) {
		    // Inside the ring - full effect
		    float t = (distance - ringInner) / ringWidth;
		    speed = glm::mix (speedInner, speedOuter, t);
		} else if (distance <= ringOuter + ringPullDistance) {
		    // Outside ring but within pull distance - attract toward ring
		    float pullT = (distance - ringOuter) / ringPullDistance;
		    speed = speedOuter * (1.0f - pullT);
		    if (distance > 0.001f) {
			glm::vec3 towardRing = -glm::normalize (radialVector);
			radialForce = towardRing * ringPullForce * pullT;
		    }
		} else {
		    // Too far from ring - no effect
		    speed = 0.0f;
		}
	    } else {
		// Standard vortex mode
		float disMid = distanceOuter - distanceInner + 0.1f;

		if (disMid < 0 || distance < distanceInner) {
		    speed = speedInner;
		} else if (distance > distanceOuter) {
		    speed = speedOuter;
		} else {
		    float t = (distance - distanceInner) / disMid;
		    speed = glm::mix (speedInner, speedOuter, t);
		}
	    }

	    p.velocity += tangent * speed * dt * speedOverride->getFloat ();

	    p.velocity += radialForce * dt * speedOverride->getFloat ();

	    if (maintainDistance && distance > 0.001f) {
		glm::vec3 towardCenter = -glm::normalize (radialVector);
		p.velocity += towardCenter * centerForce * dt * speedOverride->getFloat ();
	    }
	}
    };
}

OperatorFunc CParticle::createControlPointAttractOperator (const ControlPointAttractOperator& op) {
    int controlPoint = op.controlPoint;
    DynamicValue* originValue = op.origin->value.get ();
    DynamicValue* scaleValue = op.scale->value.get ();
    DynamicValue* thresholdValue = op.threshold->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [controlPoint, originValue, scaleValue, thresholdValue, speedOverride] (
	       std::vector<ParticleInstance>& particles, uint32_t count,
	       const std::vector<ControlPointData>& controlPoints, float currentTime, float dt
	   ) {
	glm::vec3 origin = originValue->getVec3 ();
	float scale = scaleValue->getFloat ();
	float threshold = thresholdValue->getFloat () / 2.0f;

	if (controlPoint < 0 || controlPoint >= static_cast<int> (controlPoints.size ())) {
	    return;
	}

	glm::vec3 center = controlPoints[controlPoint].position + origin;

	for (uint32_t i = 0; i < count; i++) {
	    auto& p = particles[i];
	    if (!p.alive) {
		continue;
	    }

	    glm::vec3 toCenter = center - p.position;
	    float distance = glm::length (toCenter);

	    if (distance > 0.001f && distance < threshold) {
		glm::vec3 direction = toCenter / distance;
		glm::vec3 forceVec = direction * scale * dt;
		p.velocity += forceVec * speedOverride->getFloat ();
	    }
	}
    };
}

OperatorFunc CParticle::createOscillateAlphaOperator (const OscillateAlphaOperator& op) {
    DynamicValue* freqMinValue = op.frequencyMin->value.get ();
    DynamicValue* freqMaxValue = op.frequencyMax->value.get ();
    DynamicValue* scaleMinValue = op.scaleMin->value.get ();
    DynamicValue* scaleMaxValue = op.scaleMax->value.get ();
    DynamicValue* phaseMinValue = op.phaseMin->value.get ();
    DynamicValue* phaseMaxValue = op.phaseMax->value.get ();

    return
	[this, freqMinValue, freqMaxValue, scaleMinValue, scaleMaxValue, phaseMinValue, phaseMaxValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float freqMin = freqMinValue->getFloat ();
	    float freqMax = freqMaxValue->getFloat ();
	    float scaleMin = scaleMinValue->getFloat ();
	    float scaleMax = scaleMaxValue->getFloat ();
	    float phaseMin = phaseMinValue->getFloat ();
	    float phaseMax = phaseMaxValue->getFloat ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];

		// Initialize per-particle oscillator values on first use
		if (!p.oscillateAlpha.initialized) {
		    p.oscillateAlpha.frequency = WallpaperEngine::Maths::randomFloat (m_rng, freqMin, freqMax);
		    p.oscillateAlpha.scale = WallpaperEngine::Maths::randomFloat (m_rng, scaleMin, scaleMax);
		    p.oscillateAlpha.phase
			= WallpaperEngine::Maths::randomFloat (m_rng, phaseMin, phaseMax + 2.0f * glm::pi<float> ());
		    p.oscillateAlpha.base = p.alpha;
		    p.oscillateAlpha.initialized = true;
		}

		// Cosine wave interpolating between scaleMin and scaleMax
		float w = p.oscillateAlpha.frequency;
		float t = p.age;
		float cosVal = (std::cos (w * t + p.oscillateAlpha.phase) + 1.0f) * 0.5f;
		float multiplier = glm::mix (scaleMin, scaleMax, cosVal);

		// Apply to base value (alphafade updates base each frame if present)
		p.alpha = p.oscillateAlpha.base * multiplier;
	    }
	};
}

OperatorFunc CParticle::createOscillateSizeOperator (const OscillateSizeOperator& op) {
    DynamicValue* freqMinValue = op.frequencyMin->value.get ();
    DynamicValue* freqMaxValue = op.frequencyMax->value.get ();
    DynamicValue* scaleMinValue = op.scaleMin->value.get ();
    DynamicValue* scaleMaxValue = op.scaleMax->value.get ();
    DynamicValue* phaseMinValue = op.phaseMin->value.get ();
    DynamicValue* phaseMaxValue = op.phaseMax->value.get ();

    return
	[this, freqMinValue, freqMaxValue, scaleMinValue, scaleMaxValue, phaseMinValue, phaseMaxValue] (
	    std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float, float
	) {
	    float freqMin = freqMinValue->getFloat ();
	    float freqMax = freqMaxValue->getFloat ();
	    float scaleMin = scaleMinValue->getFloat ();
	    float scaleMax = scaleMaxValue->getFloat ();
	    float phaseMin = phaseMinValue->getFloat ();
	    float phaseMax = phaseMaxValue->getFloat ();

	    for (uint32_t i = 0; i < count; i++) {
		auto& p = particles[i];

		// Initialize per-particle oscillator values on first use
		if (!p.oscillateSize.initialized) {
		    p.oscillateSize.frequency = WallpaperEngine::Maths::randomFloat (m_rng, freqMin, freqMax);
		    p.oscillateSize.scale = WallpaperEngine::Maths::randomFloat (m_rng, scaleMin, scaleMax);
		    p.oscillateSize.phase
			= WallpaperEngine::Maths::randomFloat (m_rng, phaseMin, phaseMax + 2.0f * glm::pi<float> ());
		    p.oscillateSize.base = p.size;
		    p.oscillateSize.initialized = true;
		}

		// Cosine wave interpolating between scaleMin and scaleMax
		float w = p.oscillateSize.frequency;
		float t = p.age;
		float cosVal = (std::cos (w * t + p.oscillateSize.phase) + 1.0f) * 0.5f;
		float multiplier = glm::mix (scaleMin, scaleMax, cosVal);

		// Apply to base value (sizeChange updates base each frame if present)
		p.size = p.oscillateSize.base * multiplier;
	    }
	};
}

OperatorFunc CParticle::createOscillatePositionOperator (const OscillatePositionOperator& op) {
    DynamicValue* freqMinValue = op.frequencyMin->value.get ();
    DynamicValue* freqMaxValue = op.frequencyMax->value.get ();
    DynamicValue* scaleMinValue = op.scaleMin->value.get ();
    DynamicValue* scaleMaxValue = op.scaleMax->value.get ();
    DynamicValue* phaseMinValue = op.phaseMin->value.get ();
    DynamicValue* phaseMaxValue = op.phaseMax->value.get ();
    DynamicValue* maskValue = op.mask->value.get ();
    DynamicValue* speedOverride = m_particle.instanceOverride.speed->value.get ();

    return [this, freqMinValue, freqMaxValue, scaleMinValue, scaleMaxValue, phaseMinValue, phaseMaxValue, maskValue,
	    speedOverride] (
	       std::vector<ParticleInstance>& particles, uint32_t count, const std::vector<ControlPointData>&, float,
	       float dt
	   ) {
	float freqMin = freqMinValue->getFloat ();
	float freqMax = freqMaxValue->getFloat ();
	float scaleMin = scaleMinValue->getFloat ();
	float scaleMax = scaleMaxValue->getFloat ();
	float phaseMin = phaseMinValue->getFloat ();
	float phaseMax = phaseMaxValue->getFloat ();
	glm::vec3 mask = maskValue->getVec3 ();

	for (uint32_t i = 0; i < count; i++) {
	    auto& p = particles[i];

	    // Initialize per-particle oscillator values on first use (per axis)
	    if (!p.oscillatePosition.initialized) {
		for (int axis = 0; axis < 3; axis++) {
		    p.oscillatePosition.frequency[axis] = WallpaperEngine::Maths::randomFloat (m_rng, freqMin, freqMax);
		    p.oscillatePosition.scale[axis] = WallpaperEngine::Maths::randomFloat (m_rng, scaleMin, scaleMax);
		    p.oscillatePosition.phase[axis]
			= WallpaperEngine::Maths::randomFloat (m_rng, phaseMin, phaseMax + 2.0f * glm::pi<float> ());
		}
		p.oscillatePosition.initialized = true;
	    }

	    float t = p.age;
	    glm::vec3 delta (0.0f);

	    for (int axis = 0; axis < 3; axis++) {
		float w = 2.0f * glm::pi<float> () * p.oscillatePosition.frequency[axis] / (2.0f * glm::pi<float> ());
		// Derivative of cos is -sin; multiplied by dt for position change
		float move
		    = -p.oscillatePosition.scale[axis] * w * std::sin (w * t + p.oscillatePosition.phase[axis]) * dt;
		// Apply mask as bias multiplier for this axis
		delta[axis] = move * mask[axis] * speedOverride->getFloat ();
	    }

	    p.position += delta;
	}
    };
}

// ========== RENDERING ==========

void CParticle::setupPass () {
    if (!m_particle.material || !m_particle.material->material || m_particle.material->material->passes.empty ()) {
	sLog.error ("No valid material for particle ", m_particle.name);
	return;
    }

    const auto& firstPass = **m_particle.material->material->passes.begin ();

    m_passOverride = std::make_unique<ImageEffectPassOverride> ();
    m_passOverride->combos["THICKFORMAT"] = 1;
    if (m_useRopeRenderer) {
	m_passOverride->shaderOverride = "genericropeparticle";
    }
    if (m_spritesheetFrames > 0) {
	m_passOverride->combos["SPRITESHEET"] = 1;
    }
    if (m_useTrailRenderer) {
	m_passOverride->combos["TRAILRENDERER"] = 1;
    }

    // Force texture 0 to use the input (particle texture) rather than the shader's
    // default "util/white" annotation, which would override it in setupRenderTexture()
    m_passBinds = { { 0, "previous" } };

    auto refractIt = firstPass.combos.find ("REFRACT");
    m_hasRefract = refractIt != firstPass.combos.end () && refractIt->second != 0;

    m_passFBOProvider = std::make_shared<FBOProvider> (this);

    // REFRACT: create a copy FBO shadowing _rt_FullFrameBuffer. The shader reads g_Texture3
    // (= _rt_FullFrameBuffer) while we render TO the scene FBO; reading and writing the same FBO
    // is undefined behavior in OpenGL and causes black reads on NVIDIA. Placing a copy FBO under
    // the same name in our FBOProvider makes CPass resolve g_Texture3 to the copy instead - we
    // blit the scene content into it before each render.
    if (m_hasRefract) {
	auto sceneFBO = getScene ().getFBO ();
	float w = static_cast<float> (sceneFBO->getRealWidth ());
	float h = static_cast<float> (sceneFBO->getRealHeight ());
	m_refractFBO = m_passFBOProvider->create (
	    "_rt_FullFrameBuffer", TextureFormat_ARGB8888, TextureFlags_ClampUVs, 1.0f, { w, h }, { w, h }
	);
    }

    m_pass = new Effects::CPass (*this, m_passFBOProvider, firstPass, *m_passOverride, m_passBinds, std::nullopt);

    m_pass->setDestination (getScene ().getFBO ());
    m_pass->setInput (getTexture ());

    // Set matrix pointers - CPass will dereference these each frame
    m_pass->setModelViewProjectionMatrix (&m_mvpMatrix);
    m_pass->setModelViewProjectionMatrixInverse (&m_mvpMatrixInverse);
    m_pass->setModelMatrix (&m_modelMatrix);
    m_pass->setViewProjectionMatrix (&m_viewProjectionMatrix);

    GLint prevVAO = 0;
    glGetIntegerv (GL_VERTEX_ARRAY_BINDING, &prevVAO);

    glGenVertexArrays (1, &m_vao);
    glGenBuffers (1, &m_vbo);
    glGenBuffers (1, &m_ebo);

    glBindVertexArray (m_vao);
    glBindBuffer (GL_ARRAY_BUFFER, m_vbo);
    glBindBuffer (GL_ELEMENT_ARRAY_BUFFER, m_ebo);

    const GLuint program = m_pass->getProgramID ();

    if (m_useRopeRenderer) {
	// Rope vertex layout: 7 attributes, 26 floats/vertex, stride=104 bytes
	// a_PositionVec4(4) + a_TexCoordVec4(4) + a_TexCoordVec4C1(4) + a_TexCoordVec4C2(4)
	// + a_TexCoordVec4C3(4) + a_TexCoordC4(2) + a_Color(4) = 26
	const GLsizei stride = sizeof (float) * ROPE_FLOATS_PER_VERTEX;

	const GLint loc0 = glGetAttribLocation (program, "a_PositionVec4");
	const GLint loc1 = glGetAttribLocation (program, "a_TexCoordVec4");
	const GLint loc2 = glGetAttribLocation (program, "a_TexCoordVec4C1");
	const GLint loc3 = glGetAttribLocation (program, "a_TexCoordVec4C2");
	const GLint loc4 = glGetAttribLocation (program, "a_TexCoordVec4C3");
	const GLint loc5 = glGetAttribLocation (program, "a_TexCoordC4");
	const GLint loc6 = glGetAttribLocation (program, "a_Color");

	if (loc0 >= 0) {
	    glEnableVertexAttribArray (loc0);
	    glVertexAttribPointer (loc0, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 0));
	}
	if (loc1 >= 0) {
	    glEnableVertexAttribArray (loc1);
	    glVertexAttribPointer (loc1, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 4));
	}
	if (loc2 >= 0) {
	    glEnableVertexAttribArray (loc2);
	    glVertexAttribPointer (loc2, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 8));
	}
	if (loc3 >= 0) {
	    glEnableVertexAttribArray (loc3);
	    glVertexAttribPointer (loc3, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 12));
	}
	if (loc4 >= 0) {
	    glEnableVertexAttribArray (loc4);
	    glVertexAttribPointer (loc4, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 16));
	}
	if (loc5 >= 0) {
	    glEnableVertexAttribArray (loc5);
	    glVertexAttribPointer (loc5, 2, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 20));
	}
	if (loc6 >= 0) {
	    glEnableVertexAttribArray (loc6);
	    glVertexAttribPointer (loc6, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 22));
	}
    } else {
	// Sprite vertex layout: 5 attributes, 17 floats/vertex, stride=68 bytes
	// a_Position(3) + a_TexCoordVec4(4) + a_Color(4) + a_TexCoordVec4C1(4) + a_TexCoordC2(2) = 17
	const GLsizei stride = sizeof (float) * SPRITE_FLOATS_PER_VERTEX;

	const GLint loc0 = glGetAttribLocation (program, "a_Position");
	const GLint loc1 = glGetAttribLocation (program, "a_TexCoordVec4");
	const GLint loc2 = glGetAttribLocation (program, "a_Color");
	const GLint loc3 = glGetAttribLocation (program, "a_TexCoordVec4C1");
	const GLint loc4 = glGetAttribLocation (program, "a_TexCoordC2");

	if (loc0 >= 0) {
	    glEnableVertexAttribArray (loc0);
	    glVertexAttribPointer (loc0, 3, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 0));
	}
	if (loc1 >= 0) {
	    glEnableVertexAttribArray (loc1);
	    glVertexAttribPointer (loc1, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 3));
	}
	if (loc2 >= 0) {
	    glEnableVertexAttribArray (loc2);
	    glVertexAttribPointer (loc2, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 7));
	}
	if (loc3 >= 0) {
	    glEnableVertexAttribArray (loc3);
	    glVertexAttribPointer (loc3, 4, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 11));
	}
	if (loc4 >= 0) {
	    glEnableVertexAttribArray (loc4);
	    glVertexAttribPointer (loc4, 2, GL_FLOAT, GL_FALSE, stride, (void*)(sizeof (float) * 15));
	}
    }

    glBindVertexArray (prevVAO);

    setupGeometryCallbacks ();
    setupParticleUniforms ();
}

void CParticle::setupGeometryCallbacks () {
    m_pass->setGeometryCallback (
	// Setup attribs: save current VAO, bind particle VAO
	[this] () {
	    glGetIntegerv (GL_VERTEX_ARRAY_BINDING, &m_prevVAO);
	    glBindVertexArray (m_vao);
	},
	// Draw geometry: indexed rendering
	[this] () { glDrawElements (GL_TRIANGLES, m_activeIndexCount, GL_UNSIGNED_INT, nullptr); },
	// Cleanup: restore previous VAO
	[this] () { glBindVertexArray (m_prevVAO); }
    );
}

void CParticle::setupParticleUniforms () {
    // Add particle-specific uniforms from common_particles.h that CPass doesn't provide
    // These are pointer-based: CPass reads the current value each frame
    m_pass->addUniform ("g_ModelMatrixInverse", &m_modelMatrixInverse);
    m_pass->addUniform ("g_OrientationUp", &m_orientationUp);
    m_pass->addUniform ("g_OrientationRight", &m_orientationRight);
    m_pass->addUniform ("g_OrientationForward", &m_orientationForward);
    m_pass->addUniform ("g_ViewUp", &m_viewUp);
    m_pass->addUniform ("g_ViewRight", &m_viewRight);
    m_pass->addUniform ("g_EyePosition", &m_eyePosition);
    m_pass->addUniform ("g_RenderVar0", &m_renderVar0);
    m_pass->addUniform ("g_RenderVar1", &m_renderVar1);

    // REFRACT: set g_RefractAmount (shader default 0.05, may not be applied by CPass's parameter system)
    if (m_hasRefract) {
	m_pass->addUniform ("g_RefractAmount", &m_refractAmount);
    }
}

void CParticle::updateMatrices () {
    glm::vec3 scale = m_particle.scale->value->getVec3 ();
    glm::vec3 angles = m_particle.angles->value->getVec3 ();

    m_modelMatrix = glm::mat4 (1.0f);
    m_modelMatrix = glm::translate (m_modelMatrix, m_transformedOrigin);
    this->applyParallaxToModelMatrix ();

    // Negate X and Z rotations to account for Y-flipped coordinate system
    m_modelMatrix = glm::rotate (m_modelMatrix, -angles.z, glm::vec3 (0, 0, 1));
    m_modelMatrix = glm::rotate (m_modelMatrix, angles.y, glm::vec3 (0, 1, 0));
    m_modelMatrix = glm::rotate (m_modelMatrix, -angles.x, glm::vec3 (1, 0, 0));
    m_modelMatrix = glm::scale (m_modelMatrix, scale);
    m_modelMatrixInverse = glm::inverse (m_modelMatrix);

    this->updateParticleViewProjection ();
    m_mvpMatrix = m_viewProjectionMatrix * m_modelMatrix;
    m_mvpMatrixInverse = glm::inverse (m_mvpMatrix);

    m_orientationUp = glm::vec3 (0.0f, 1.0f, 0.0f);
    m_orientationRight = glm::vec3 (1.0f, 0.0f, 0.0f);
    m_orientationForward = glm::vec3 (0.0f, 0.0f, 1.0f);
    m_viewUp = glm::vec3 (0.0f, 1.0f, 0.0f);
    m_viewRight = glm::vec3 (1.0f, 0.0f, 0.0f);

    this->updateParticleRenderVars ();
}

void CParticle::applyParallaxToModelMatrix () {
    // CScene::renderFrame() already folds disableparallax into getParallaxDisplacement()
    if (!getScene ().getScene ().camera.parallax.enabled->value->getBool ()) {
	return;
    }

    const glm::vec2 offset = getScene ().getParallaxOffset (m_particle);
    const glm::vec3 parallaxOffset { offset.x, offset.y, 0.0f };
    m_modelMatrix = glm::translate (m_modelMatrix, parallaxOffset);
}

void CParticle::updateParticleViewProjection () {
    if ((m_particle.flags & 4) != 0) {
	// Perspective particles use a dedicated perspective projection
	float width = getScene ().getCamera ().getWidth ();
	float height = getScene ().getCamera ().getHeight ();
	float aspect = width / height;
	float fov = glm::radians (getScene ().getCamera ().getFov ());
	float nearz = getScene ().getCamera ().getNearZ ();
	float farz = getScene ().getCamera ().getFarZ ();

	glm::mat4 perspectiveProj = glm::perspective (fov, aspect, nearz, farz);
	glm::mat4 perspectiveView
	    = glm::lookAt (glm::vec3 (0.0f, 0.0f, 1000.0f), glm::vec3 (0.0f, 0.0f, 0.0f), glm::vec3 (0.0f, 1.0f, 0.0f));

	m_viewProjectionMatrix = perspectiveProj * perspectiveView;
	m_eyePosition = glm::vec3 (0.0f, 0.0f, 1000.0f);
    } else {
	// Orthographic projection from scene camera
	m_viewProjectionMatrix = getScene ().getCamera ().getProjection () * getScene ().getCamera ().getLookAt ();
	// The shader's ComputeParticleTrailTangents computes trail ribbon width via
	// cross(eyeDirection, velocity). With the ortho eye at (0,0,0) and particles at z=0,
	// eyeDirection is purely XY, so the cross product is Z-only and invisible under
	// orthographic projection. Placing the eye at z=1000 gives it a visible XY component.
	m_eyePosition = glm::vec3 (0.0f, 0.0f, 1000.0f);
    }
}

void CParticle::updateParticleRenderVars () {
    m_renderVar0 = glm::vec4 (m_trailLength, m_trailMaxLength, m_trailMinLength, 0.0f);

    if (m_spritesheetFrames > 0 && m_spritesheetCols > 0 && m_spritesheetRows > 0) {
	float frameWidth = 1.0f / static_cast<float> (m_spritesheetCols);
	float frameHeight = 1.0f / static_cast<float> (m_spritesheetRows);
	float textureRatio = 1.0f;
	if (const auto texture = getTexture ()) {
	    // Use atlas dimensions (resolution vec4) rather than getRealWidth/Height, which
	    // returns per-frame dimensions for animated textures - the shader needs the
	    // per-frame pixel aspect ratio: (atlasH * frameHeight) / (atlasW * frameWidth).
	    const glm::vec4* res = texture->getResolution ();
	    float w = res->x;
	    float h = res->y;
	    if (w > 0.0f) {
		textureRatio = (h * frameHeight) / (w * frameWidth);
	    }
	}
	m_renderVar1 = glm::vec4 (frameWidth, frameHeight, static_cast<float> (m_spritesheetFrames), textureRatio);
    } else {
	float textureRatio = 1.0f;
	if (const auto texture = getTexture ()) {
	    float w = static_cast<float> (texture->getRealWidth ());
	    float h = static_cast<float> (texture->getRealHeight ());
	    if (w > 0.0f) {
		textureRatio = h / w;
	    }
	}
	m_renderVar1 = glm::vec4 (0.0f, 0.0f, 0.0f, textureRatio);
    }
}

void CParticle::renderSprites () {
    if (m_particleCount == 0 || m_pass == nullptr) {
	return;
    }

    uint32_t aliveCount = 0;
    for (uint32_t i = 0; i < m_particleCount; i++) {
	if (m_particles[i].alive) {
	    aliveCount++;
	}
    }

    if (aliveCount == 0) {
	return;
    }

    // Build vertex data in WP shader layout:
    // a_Position(3) + a_TexCoordVec4(uv.x, uv.y, rotZ, size)(4) + a_Color(4)
    //   + a_TexCoordVec4C1(vel.x, vel.y, vel.z, lifetime)(4) + a_TexCoordC2(rotX, rotY)(2) = 17 floats
    uint32_t vertexIndex = 0;
    uint32_t indexOffset = 0;

    for (uint32_t i = 0; i < m_particleCount; i++) {
	const auto& p = m_particles[i];
	if (!p.alive) {
	    continue;
	}

	// Skip particles with invalid values
	if (!std::isfinite (p.position.x) || !std::isfinite (p.position.y) || !std::isfinite (p.position.z)
	    || !std::isfinite (p.size) || p.size <= 0.0f || p.size > 10000.0f) {
	    continue;
	}

	// Encode the CPU-computed frame (accounts for sequenceMultiplier and animation mode)
	// into the lifetime value the WP shader's ComputeSpriteFrame expects: it derives the
	// current frame via floor(frac(lifetime) * numFrames) and the inter-frame blend via
	// frac(lifetime * numFrames).
	float lifetime = p.getLifetimePos ();

	if (m_spritesheetFrames > 0 && p.frame >= 0.0f) {
	    if (m_particle.animationMode == "randomframe") {
		// Center within the frame to avoid floating-point edge cases
		lifetime = (p.frame + 0.5f) / static_cast<float> (m_spritesheetFrames);
	    } else {
		lifetime = p.frame / static_cast<float> (m_spritesheetFrames);
	    }
	}

	auto addVertex = [&] (float u, float v) {
	    const uint32_t base = vertexIndex * SPRITE_FLOATS_PER_VERTEX;
	    // a_Position (vec3)
	    m_vertices[base + 0] = p.position.x;
	    m_vertices[base + 1] = p.position.y;
	    m_vertices[base + 2] = p.position.z;
	    // a_TexCoordVec4 (vec4: uv.x, uv.y, rotZ, size)
	    m_vertices[base + 3] = u;
	    m_vertices[base + 4] = v;
	    m_vertices[base + 5] = p.rotation.z;
	    m_vertices[base + 6] = p.size;
	    // a_Color (vec4: r, g, b, a)
	    m_vertices[base + 7] = p.color.r;
	    m_vertices[base + 8] = p.color.g;
	    m_vertices[base + 9] = p.color.b;
	    m_vertices[base + 10] = p.alpha;
	    // a_TexCoordVec4C1 (vec4: vel.x, vel.y, vel.z, lifetime)
	    m_vertices[base + 11] = p.velocity.x;
	    m_vertices[base + 12] = p.velocity.y;
	    m_vertices[base + 13] = p.velocity.z;
	    m_vertices[base + 14] = lifetime;
	    // a_TexCoordC2 (vec2: rotX, rotY)
	    m_vertices[base + 15] = p.rotation.x;
	    m_vertices[base + 16] = p.rotation.y;
	    vertexIndex++;
	};

	uint32_t baseVertex = vertexIndex;
	addVertex (0.0f, 1.0f); // 0: Bottom-left
	addVertex (1.0f, 1.0f); // 1: Bottom-right
	addVertex (1.0f, 0.0f); // 2: Top-right
	addVertex (0.0f, 0.0f); // 3: Top-left

	m_indices[indexOffset++] = baseVertex + 0;
	m_indices[indexOffset++] = baseVertex + 1;
	m_indices[indexOffset++] = baseVertex + 2;
	m_indices[indexOffset++] = baseVertex + 2;
	m_indices[indexOffset++] = baseVertex + 3;
	m_indices[indexOffset++] = baseVertex + 0;
    }

    m_activeIndexCount = static_cast<GLsizei> (indexOffset);
    if (m_activeIndexCount == 0) {
	return;
    }

#if !NDEBUG
    std::string str = "Particles ";
    str += this->getParticle ().name + " (" + std::to_string (this->getId ()) + ", " + this->getParticle ().particleFile
	+ ")";
    glPushDebugGroup (GL_DEBUG_SOURCE_APPLICATION, 0, -1, str.c_str ());
#endif

    glBindBuffer (GL_ARRAY_BUFFER, m_vbo);
    glBufferData (
	GL_ARRAY_BUFFER, static_cast<GLsizeiptr> (vertexIndex * SPRITE_FLOATS_PER_VERTEX * sizeof (float)),
	m_vertices.data (), GL_DYNAMIC_DRAW
    );

    glBindBuffer (GL_ELEMENT_ARRAY_BUFFER, m_ebo);
    glBufferData (
	GL_ELEMENT_ARRAY_BUFFER, static_cast<GLsizeiptr> (indexOffset * sizeof (uint32_t)), m_indices.data (),
	GL_DYNAMIC_DRAW
    );

    updateMatrices ();

    // REFRACT: blit current scene content into the copy FBO first, giving the shader a
    // snapshot of what's behind the particles without a read/write feedback loop
    if (m_hasRefract && m_refractFBO) {
	auto sceneFBO = getScene ().getFBO ();
	GLint w = static_cast<GLint> (sceneFBO->getRealWidth ());
	GLint h = static_cast<GLint> (sceneFBO->getRealHeight ());
	glBindFramebuffer (GL_READ_FRAMEBUFFER, sceneFBO->getFramebuffer ());
	glBindFramebuffer (GL_DRAW_FRAMEBUFFER, m_refractFBO->getFramebuffer ());
	glBlitFramebuffer (0, 0, w, h, 0, 0, w, h, GL_COLOR_BUFFER_BIT, GL_NEAREST);
    }

    // ComputeParticleTrailTangents produces a right vector with a Z component (from
    // cross(eyeDirection, velocity), where eyeDirection has an XY offset from the model
    // transform). For 2D/ortho particles at z=0, the ortho near plane sits at ndc.z=-1, so any
    // Z offset pushes vertices past it and clips half the quad. GL_DEPTH_CLAMP avoids that by
    // clamping depth instead of clipping.
    glEnable (GL_DEPTH_CLAMP);

    // CPass::render() handles: FBO binding, texture setup, uniforms, blending, draw call, cleanup
    m_pass->render ();

    glDisable (GL_DEPTH_CLAMP);

#if !NDEBUG
    glPopDebugGroup ();
#endif
}

void CParticle::renderRope () {
    if (m_particleCount < 2 || m_pass == nullptr) {
	return;
    }

    // Already in spawn order (oldest at index 0) thanks to compaction in update();
    // all particles in [0, m_particleCount) are alive.
    const uint32_t aliveCount = m_particleCount;

    // Each segment between consecutive particles is subdivided into m_ropeSubdivision
    // sub-segments via Catmull-Rom spline, for smooth curves instead of harsh corners.
    //
    // Rope vertex layout (26 floats per vertex, THICKFORMAT):
    // [0-3]   a_PositionVec4:   startPos.xyz, sizeStart
    // [4-7]   a_TexCoordVec4:   endPos.xyz, trailLength
    // [8-11]  a_TexCoordVec4C1: CP0.xyz, trailPosition
    // [12-15] a_TexCoordVec4C2: CP1.xyz, sizeEnd
    // [16-19] a_TexCoordVec4C3: colorEnd.rgba
    // [20-21] a_TexCoordC4:     uvs.xy
    // [22-25] a_Color:          colorStart.rgba

    const uint32_t numSegments = aliveCount - 1;
    const int subdivision = std::max (1, m_ropeSubdivision);

    auto catmullRom = [] (const glm::vec3& p0, const glm::vec3& p1, const glm::vec3& p2, const glm::vec3& p3,
			  float t) -> glm::vec3 {
	float t2 = t * t, t3 = t2 * t;
	return 0.5f
	    * ((2.0f * p1) + (-p0 + p2) * t + (2.0f * p0 - 5.0f * p1 + 4.0f * p2 - p3) * t2
	       + (-p0 + 3.0f * p1 - 3.0f * p2 + p3) * t3);
    };

    // First pass: evaluate the spline to get all interpolated points (position, size, color)
    const uint32_t totalPoints = numSegments * subdivision + 1;
    this->m_splinePositions.resize (totalPoints);
    this->m_splineSizes.resize (totalPoints);
    this->m_splineColors.resize (totalPoints);
    auto& splinePositions = this->m_splinePositions;
    auto& splineSizes = this->m_splineSizes;
    auto& splineColors = this->m_splineColors;

    for (uint32_t i = 0; i < numSegments; i++) {
	const auto& p1 = m_particles[i];
	const auto& p2 = m_particles[i + 1];
	const auto& p0 = (i > 0) ? m_particles[i - 1] : p1;
	const auto& p3 = (i + 2 < aliveCount) ? m_particles[i + 2] : p2;

	for (int k = 0; k < subdivision; k++) {
	    float t = static_cast<float> (k) / static_cast<float> (subdivision);
	    uint32_t idx = i * subdivision + k;

	    splinePositions[idx] = catmullRom (p0.position, p1.position, p2.position, p3.position, t);
	    splineSizes[idx] = glm::mix (p1.size, p2.size, t);
	    splineColors[idx] = glm::mix (glm::vec4 (p1.color, p1.alpha), glm::vec4 (p2.color, p2.alpha), t);
	}
    }
    // Last point is the final particle
    {
	const auto& pLast = m_particles[aliveCount - 1];
	splinePositions[totalPoints - 1] = pLast.position;
	splineSizes[totalPoints - 1] = pLast.size;
	splineColors[totalPoints - 1] = glm::vec4 (pLast.color, pLast.alpha);
    }

    // Second pass: build quads from consecutive spline points. The shader computes UV.v as
    // trailPosition / (trailLength - 1), so trailLength/trailPosition are expressed in
    // sub-segment units for the correct UV slice per quad. UV scale divides the effective
    // length, pushing UVs past [0,1] so the texture repeats.
    uint32_t vertexIndex = 0;
    uint32_t indexOffset = 0;
    const uint32_t totalSubSegments = totalPoints - 1;
    const float uvScale = (m_ropeUVScale > 0.0f) ? m_ropeUVScale : 1.0f;
    const float trailLength = static_cast<float> (totalSubSegments) / uvScale + 1.0f;
    const float usableLength = trailLength - 1.0f;

    // UV smoothing: distribute UV proportional to arc length instead of uniform index.
    // Per wiki: only when all particle lifetimes match and scrolling is disabled.
    const bool useSmoothing = m_ropeUVSmoothing && m_uniformLifetimes && !m_ropeUVScrolling;
    auto& cumulativeArcLength = this->m_cumulativeArcLength;
    float totalArcLength = 0.0f;

    if (useSmoothing) {
	cumulativeArcLength.resize (totalPoints, 0.0f);
	for (uint32_t i = 1; i < totalPoints; i++) {
	    totalArcLength += glm::distance (splinePositions[i], splinePositions[i - 1]);
	    cumulativeArcLength[i] = totalArcLength;
	}
    }

    // UV scrolling: shift UV along the rope over time (1 UV cycle per second)
    float scrollOffset = 0.0f;
    if (m_ropeUVScrolling && usableLength > 0.0f) {
	scrollOffset = std::fmod (static_cast<float> (g_Time), 10000.0f) * usableLength;
    }

    for (uint32_t s = 0; s < totalSubSegments; s++) {
	const glm::vec3& posStart = splinePositions[s];
	const glm::vec3& posEnd = splinePositions[s + 1];
	float sizeStart = splineSizes[s];
	float sizeEnd = splineSizes[s + 1];
	const glm::vec4& colorStart = splineColors[s];
	const glm::vec4& colorEnd = splineColors[s + 1];

	// Neighboring points for shader tangent computation (CP0/CP1)
	const glm::vec3& posPrev = (s > 0) ? splinePositions[s - 1] : posStart;
	const glm::vec3& posAfter = (s + 2 < totalPoints) ? splinePositions[s + 2] : posEnd;

	// Compute trailPosition for UV mapping
	float trailPosition;
	if (useSmoothing && totalArcLength > 0.0f) {
	    // Arc-length parameterization: map cumulative distance to sub-segment space
	    trailPosition = cumulativeArcLength[s] / totalArcLength * static_cast<float> (totalSubSegments);
	} else {
	    trailPosition = static_cast<float> (s);
	}
	trailPosition += scrollOffset;

	auto addRopeVertex = [&] (float uvX, float uvY) {
	    const uint32_t base = vertexIndex * ROPE_FLOATS_PER_VERTEX;

	    // a_PositionVec4: startPos.xyz, sizeStart
	    m_vertices[base + 0] = posStart.x;
	    m_vertices[base + 1] = posStart.y;
	    m_vertices[base + 2] = posStart.z;
	    m_vertices[base + 3] = sizeStart;

	    // a_TexCoordVec4: endPos.xyz, trailLength
	    m_vertices[base + 4] = posEnd.x;
	    m_vertices[base + 5] = posEnd.y;
	    m_vertices[base + 6] = posEnd.z;
	    m_vertices[base + 7] = trailLength;

	    // a_TexCoordVec4C1: CP0.xyz (neighbor before start), trailPosition
	    m_vertices[base + 8] = posPrev.x;
	    m_vertices[base + 9] = posPrev.y;
	    m_vertices[base + 10] = posPrev.z;
	    m_vertices[base + 11] = trailPosition;

	    // a_TexCoordVec4C2: CP1.xyz (neighbor after end), sizeEnd
	    m_vertices[base + 12] = posAfter.x;
	    m_vertices[base + 13] = posAfter.y;
	    m_vertices[base + 14] = posAfter.z;
	    m_vertices[base + 15] = sizeEnd;

	    // a_TexCoordVec4C3: colorEnd.rgba
	    m_vertices[base + 16] = colorEnd.r;
	    m_vertices[base + 17] = colorEnd.g;
	    m_vertices[base + 18] = colorEnd.b;
	    m_vertices[base + 19] = colorEnd.a;

	    // a_TexCoordC4: uvs.xy
	    m_vertices[base + 20] = uvX;
	    m_vertices[base + 21] = uvY;

	    // a_Color: colorStart.rgba
	    m_vertices[base + 22] = colorStart.r;
	    m_vertices[base + 23] = colorStart.g;
	    m_vertices[base + 24] = colorStart.b;
	    m_vertices[base + 25] = colorStart.a;

	    vertexIndex++;
	};

	// Quad: 4 vertices (left/right at start/end of segment)
	uint32_t baseVertex = vertexIndex;
	addRopeVertex (0.0f, 0.0f); // left at start
	addRopeVertex (1.0f, 0.0f); // right at start
	addRopeVertex (1.0f, 1.0f); // right at end
	addRopeVertex (0.0f, 1.0f); // left at end

	m_indices[indexOffset++] = baseVertex + 0;
	m_indices[indexOffset++] = baseVertex + 1;
	m_indices[indexOffset++] = baseVertex + 2;
	m_indices[indexOffset++] = baseVertex + 2;
	m_indices[indexOffset++] = baseVertex + 3;
	m_indices[indexOffset++] = baseVertex + 0;
    }

    m_activeIndexCount = static_cast<GLsizei> (indexOffset);
    if (m_activeIndexCount == 0) {
	return;
    }

#if !NDEBUG
    std::string str = "Rope particles ";
    str += this->getParticle ().name + " (" + std::to_string (this->getId ()) + ", " + this->getParticle ().particleFile
	+ ")";
    glPushDebugGroup (GL_DEBUG_SOURCE_APPLICATION, 0, -1, str.c_str ());
#endif

    glBindBuffer (GL_ARRAY_BUFFER, m_vbo);
    glBufferData (
	GL_ARRAY_BUFFER, static_cast<GLsizeiptr> (vertexIndex * ROPE_FLOATS_PER_VERTEX * sizeof (float)),
	m_vertices.data (), GL_DYNAMIC_DRAW
    );

    glBindBuffer (GL_ELEMENT_ARRAY_BUFFER, m_ebo);
    glBufferData (
	GL_ELEMENT_ARRAY_BUFFER, static_cast<GLsizeiptr> (indexOffset * sizeof (uint32_t)), m_indices.data (),
	GL_DYNAMIC_DRAW
    );

    updateMatrices ();

    // REFRACT: blit current scene content into the copy FBO before rendering
    if (m_hasRefract && m_refractFBO) {
	auto sceneFBO = getScene ().getFBO ();
	GLint w = static_cast<GLint> (sceneFBO->getRealWidth ());
	GLint h = static_cast<GLint> (sceneFBO->getRealHeight ());
	glBindFramebuffer (GL_READ_FRAMEBUFFER, sceneFBO->getFramebuffer ());
	glBindFramebuffer (GL_DRAW_FRAMEBUFFER, m_refractFBO->getFramebuffer ());
	glBlitFramebuffer (0, 0, w, h, 0, 0, w, h, GL_COLOR_BUFFER_BIT, GL_NEAREST);
    }

    glEnable (GL_DEPTH_CLAMP);
    m_pass->render ();
    glDisable (GL_DEPTH_CLAMP);

#if !NDEBUG
    glPopDebugGroup ();
#endif
}