SLAM-Cross/Controls/WaveformControl.cs

using System;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Media;

namespace SlamCross.Controls;

public sealed class WaveformControl : Control
{
    private (float Low, float High)[] _peaks = Array.Empty<(float, float)>();
    private double _startNorm;
    private double _endNorm = 1.0;
    private bool _dragging;
    private double _dragOriginNorm;

    private static readonly IBrush BgBrush = new SolidColorBrush(Color.FromRgb(18, 18, 28));
    private static readonly IBrush SelBgBrush = new SolidColorBrush(Color.FromArgb(50, 80, 160, 255));
    private static readonly IBrush WaveBrush = new SolidColorBrush(Color.FromRgb(40, 100, 180));
    private static readonly IBrush SelWaveBrush = new SolidColorBrush(Color.FromRgb(100, 180, 255));
    private static readonly IPen StartPen = new Pen(Brushes.LimeGreen, 2);
    private static readonly IPen EndPen = new Pen(Brushes.OrangeRed, 2);

    public event Action<double, double>? SelectionChanged;

    public (double Start, double End) Selection => (_startNorm, _endNorm);

    public void SetPeaks((float Low, float High)[] peaks)
    {
        _peaks = peaks;
        InvalidateVisual();
    }

    public void SetSelection(double startNorm, double endNorm)
    {
        _startNorm = Math.Clamp(startNorm, 0, 1);
        _endNorm = Math.Clamp(endNorm, 0, 1);
        InvalidateVisual();
    }

    private double XToNorm(double x) => Math.Clamp(x / Bounds.Width, 0, 1);
    private double NormToX(double n) => n * Bounds.Width;

    public override void Render(DrawingContext ctx)
    {
        var w = Bounds.Width;
        var h = Bounds.Height;
        if (w <= 0 || h <= 0) return;

        ctx.FillRectangle(BgBrush, new Rect(0, 0, w, h));

        if (_peaks.Length == 0) return;

        double midY = h / 2.0;
        double startX = NormToX(_startNorm);
        double endX = NormToX(_endNorm);

        double selW = Math.Max(1, endX - startX);
        ctx.FillRectangle(SelBgBrush, new Rect(startX, 0, selW, h));

        int iw = (int)w;
        for (int px = 0; px < iw; px++)
        {
            int peakIdx = (int)((double)px / iw * _peaks.Length);
            if (peakIdx >= _peaks.Length) break;
            var (lo, hi) = _peaks[peakIdx];
            double top = midY - hi * midY;
            double bot = midY - lo * midY;
            bool inSel = px >= startX - 0.5 && px <= endX + 0.5;
            ctx.FillRectangle(inSel ? SelWaveBrush : WaveBrush,
                new Rect(px, top, 1, Math.Max(1, bot - top)));
        }

        ctx.DrawLine(StartPen, new Point(startX, 0), new Point(startX, h));
        ctx.DrawLine(EndPen, new Point(endX, 0), new Point(endX, h));
    }

    protected override void OnPointerPressed(PointerPressedEventArgs e)
    {
        base.OnPointerPressed(e);
        if (_peaks.Length == 0) return;
        _dragging = true;
        _dragOriginNorm = XToNorm(e.GetPosition(this).X);
        _startNorm = _dragOriginNorm;
        _endNorm = _dragOriginNorm;
        InvalidateVisual();
        e.Pointer.Capture(this);
        e.Handled = true;
    }

    protected override void OnPointerMoved(PointerEventArgs e)
    {
        base.OnPointerMoved(e);
        if (!_dragging) return;
        double norm = XToNorm(e.GetPosition(this).X);
        _startNorm = Math.Min(norm, _dragOriginNorm);
        _endNorm = Math.Max(norm, _dragOriginNorm);
        InvalidateVisual();
    }

    protected override void OnPointerReleased(PointerReleasedEventArgs e)
    {
        base.OnPointerReleased(e);
        if (!_dragging) return;
        _dragging = false;
        e.Pointer.Capture(null);
        SelectionChanged?.Invoke(_startNorm, _endNorm);
        e.Handled = true;
    }
}