1 files changed, 71 insertions, 0 deletions
diff --git a/src/Godosa.Desktop/GpuTimer.cs b/src/Godosa.Desktop/GpuTimer.cs
new file mode 100644
index 0000000..11076e8
--- /dev/null
+++ b/src/Godosa.Desktop/GpuTimer.cs
@@ -0,0 +1,71 @@
+using System;
+using Silk.NET.OpenGL;
+
+namespace Godosa.Desktop;
+
+/// <summary>GPU time per frame from GL_TIME_ELAPSED queries (game-loop spec §6). A small
+/// ring so reading a result never stalls on the frame still in flight; disables itself
+/// when the context has no timer queries (e.g. GLES without the extension).</summary>
+public sealed class GpuTimer
+{
+    private const int Ring = 4;
+    private readonly uint[] _queries = new uint[Ring];
+    private readonly bool[] _pending = new bool[Ring];
+    private int _current;
+    private bool _open;
+
+    public bool Supported { get; private set; }
+
+    public void Init(GL gl)
+    {
+        try
+        {
+            string version = gl.GetStringS(StringName.Version) ?? "";
+            if (version.Contains("OpenGL ES", StringComparison.Ordinal)) return;
+            for (int i = 0; i < Ring; i++) _queries[i] = gl.GenQuery();
+            Supported = gl.GetError() == GLEnum.NoError;
+        }
+        catch (Exception)
+        {
+            Supported = false;
+        }
+    }
+
+    public void Begin(GL gl)
+    {
+        if (!Supported || _pending[_current]) return; // slot still in flight: skip this frame
+        gl.BeginQuery(QueryTarget.TimeElapsed, _queries[_current]);
+        _open = true;
+    }
+
+    public void End(GL gl)
+    {
+        if (!_open) return;
+        gl.EndQuery(QueryTarget.TimeElapsed);
+        _pending[_current] = true;
+        _open = false;
+        _current = (_current + 1) % Ring;
+    }
+
+    /// <summary>Seconds for each finished query since the last call.</summary>
+    public void Collect(GL gl, Action<double> onResult)
+    {
+        if (!Supported) return;
+        for (int i = 0; i < Ring; i++)
+        {
+            if (!_pending[i]) continue;
+            gl.GetQueryObject(_queries[i], QueryObjectParameterName.ResultAvailable, out int available);
+            if (available == 0) continue;
+            gl.GetQueryObject(_queries[i], QueryObjectParameterName.Result, out ulong nanoseconds);
+            _pending[i] = false;
+            onResult(nanoseconds / 1e9);
+        }
+    }
+
+    public void Delete(GL gl)
+    {
+        if (!Supported) return;
+        for (int i = 0; i < Ring; i++) gl.DeleteQuery(_queries[i]);
+        Supported = false;
+    }
+}