Substation/HeatMap.cs

using System.Drawing.Drawing2D;

namespace Substation;

public class HeatMap : Panel
{
    record Tick(byte[] Freq, byte[] Intensity);

    readonly List<Tick> _history = new();
    readonly int _maxTicks;

    public HeatMap(int maxTicks = 60)
    {
        _maxTicks = maxTicks;
        DoubleBuffered = true;
        BackColor = Color.FromArgb(20, 20, 22);
    }

    public void AddTick(byte[] freq, byte[] intensity, bool active)
    {
        if (_history.Count >= _maxTicks)
            _history.RemoveAt(0);

        if (active)
            _history.Add(new Tick(freq, intensity));
        else
            _history.Add(new Tick(Array.Empty<byte>(), Array.Empty<byte>()));

        Invalidate();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        var g = e.Graphics;
        g.SmoothingMode = SmoothingMode.None;

        int w = Width;
        int h = Height;
        int colW = Math.Max(1, w / _maxTicks);

        // Draw axis labels
        using var font = new Font(FontFamily.GenericMonospace, 7);
        using var textBrush = new SolidBrush(Color.FromArgb(100, 100, 100));
        g.DrawString("100Hz", font, textBrush, 2, 2);
        g.DrawString("1Hz", font, textBrush, 2, h - 14);

        int plotX = 36;
        int plotW = w - plotX - 4;
        int plotH = h - 4;
        colW = Math.Max(1, plotW / _maxTicks);

        for (int i = 0; i < _history.Count; i++)
        {
            var tick = _history[i];
            int xPos = plotX + i * colW;

            if (tick.Freq.Length == 0)
            {
                // Inactive — dark cell
                using var dark = new SolidBrush(Color.FromArgb(25, 25, 28));
                g.FillRectangle(dark, xPos, 2, colW, plotH);
                continue;
            }

            // 4 sub-ticks side by side within the column
            int subW = Math.Max(1, colW / 4);
            for (int s = 0; s < 4; s++)
            {
                int freq = tick.Freq[s];   // 10-240
                int inten = tick.Intensity[s]; // 0-100
                if (inten > 100) inten = 0; // 101 sentinel = off

                // Map freq byte (10-240) to Y position (top=high freq, bottom=low freq)
                float normFreq = (freq - 10f) / (240f - 10f);
                int y = (int)(2 + plotH * (1f - normFreq));
                if (y < 2) y = 2;
                if (y > plotH) y = plotH;

                var color = HeatColor(inten);
                using var brush = new SolidBrush(color);
                g.FillRectangle(brush, xPos + s * subW, y, subW, 3);
            }
        }
    }

    static Color HeatColor(int intensity)
    {
        // 0=black, 30=blue, 60=green, 80=gold, 100=red
        if (intensity <= 0) return Color.FromArgb(20, 20, 22);
        if (intensity < 30)
        {
            float t = intensity / 30f;
            return Color.FromArgb(0, (int)(50 * t), (int)(80 + 80 * t));
        }
        if (intensity < 60)
        {
            float t = (intensity - 30) / 30f;
            return Color.FromArgb((int)(60 * t), (int)(130 + 80 * t), (int)(160 - 100 * t));
        }
        if (intensity < 80)
        {
            float t = (intensity - 60) / 20f;
            return Color.FromArgb((int)(60 + 180 * t), 210, (int)(60 - 30 * t));
        }
        float t2 = (intensity - 80) / 20f;
        return Color.FromArgb(255, (int)(240 - 140 * t2), (int)(30 - 10 * t2));
    }
}