From 39066900773e7857faf2d02e7ed51b71d219d97d Mon Sep 17 00:00:00 2001
From: godosa <godosa@godosa.eu>
Date: Tue, 6 Oct 2026 23:39:36 +0200
Subject: godosa-engine: initial public history

---
 src/Godosa.Desktop/FrameTimeGraph.cs | 65 ++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 src/Godosa.Desktop/FrameTimeGraph.cs

(limited to 'src/Godosa.Desktop/FrameTimeGraph.cs')

diff --git a/src/Godosa.Desktop/FrameTimeGraph.cs b/src/Godosa.Desktop/FrameTimeGraph.cs
new file mode 100644
index 0000000..7e59a17
--- /dev/null
+++ b/src/Godosa.Desktop/FrameTimeGraph.cs
@@ -0,0 +1,65 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Media;
+using Godosa.Core.Diagnostics;
+
+namespace Godosa.Desktop;
+
+/// <summary>
+/// Frame-time bar graph (game-loop spec §5): one 1-px bar per frame in the
+/// stats window, newest at the right, 0–50 ms scale, dashed guides at 16.7 ms
+/// (60 fps) and 33.3 ms (30 fps). Bars are colored relative to the window
+/// median (green ≤ 1.5×, yellow ≤ 2×, red = hitch) so ordinary vsync jitter
+/// stays green whatever the refresh rate. Drawn by Avalonia, not GL, so it
+/// doesn't perturb the GL frames it measures. Presentation only.
+/// </summary>
+public sealed class FrameTimeGraph : Control
+{
+    private const float ScaleMs = 50f;
+    private const float Ms60 = 1000f / 60f;
+    private const float Ms30 = 1000f / 30f;
+
+    private static readonly IBrush Backdrop = new SolidColorBrush(Color.FromArgb(90, 255, 255, 255));
+    private static readonly IBrush Good = new SolidColorBrush(Color.FromRgb(80, 200, 120));
+    private static readonly IBrush Slow = new SolidColorBrush(Color.FromRgb(230, 200, 60));
+    private static readonly IBrush Bad = new SolidColorBrush(Color.FromRgb(230, 70, 60));
+    private static readonly IPen Guide = new Pen(new SolidColorBrush(Color.FromArgb(170, 255, 255, 255)), 1, DashStyle.Dash);
+
+    private readonly FrameTimeStats _stats;
+    private readonly float[] _buffer;
+
+    public FrameTimeGraph(FrameTimeStats stats)
+    {
+        _stats = stats;
+        _buffer = new float[stats.Capacity];
+        Width = stats.Capacity;
+        Height = 60;
+    }
+
+    public override void Render(DrawingContext context)
+    {
+        double w = Bounds.Width, h = Bounds.Height;
+        context.FillRectangle(Backdrop, new Rect(0, 0, w, h));
+
+        int n = _stats.CopyIntervalsMs(_buffer);
+        float median = (float)_stats.Summarize().P50Ms;
+        double x0 = w - n;
+        for (int i = 0; i < n; i++)
+        {
+            float ms = _buffer[i];
+            double barHeight = Math.Min(ms / ScaleMs, 1f) * h;
+            var brush = ms > 2f * median ? Bad : ms > 1.5f * median ? Slow : Good;
+            context.FillRectangle(brush, new Rect(x0 + i, h - barHeight, 1, barHeight));
+        }
+
+        DrawGuide(context, Ms60, w, h);
+        DrawGuide(context, Ms30, w, h);
+    }
+
+    private static void DrawGuide(DrawingContext context, float ms, double w, double h)
+    {
+        double y = h - ms / ScaleMs * h;
+        context.DrawLine(Guide, new Point(0, y), new Point(w, y));
+    }
+}
-- 
cgit