phase(N.5) Task 12: CPU stopwatch + GL_TIME_ELAPSED queries in [WB-DIAG]

Adds median + 95th-percentile CPU + GPU dispatch time to the existing
5-second [WB-DIAG] rollup. CPU via Stopwatch (always running, cheap;
only logged under ACDREAM_WB_DIAG=1). GPU via two GL_TIME_ELAPSED
queries (opaque + transparent) wrapping each glMultiDrawElementsIndirect,
polled non-blocking via QueryResultAvailable on the next frame.

Sample window is 256 frames per signal; median + p95 reported.
Numbers populate the SHIP commit's perf table at Task 19.

Silk.NET naming note: GL_TIME_ELAPSED queries use QueryTarget.TimeElapsed
(confirmed present in Silk.NET.OpenGL 2.23.0 DLL). The 64-bit result is
read via GetQueryObject(..., out ulong) which dispatches to
glGetQueryObjectui64v; the int overload (glGetQueryObjectiv) is used for
the ResultAvailable poll, matching WorldBuilder's VisibilityManager pattern.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs

@@ -112,6 +112,16 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
     private int _instancesIssued;
     private long _lastLogTick;
 
+    // CPU + GPU timing for [WB-DIAG] under ACDREAM_WB_DIAG=1.
+    private readonly System.Diagnostics.Stopwatch _cpuStopwatch = new();
+    private readonly long[] _cpuSamples = new long[256];   // microseconds
+    private int _cpuSampleCursor;
+    private uint _gpuQueryOpaque;
+    private uint _gpuQueryTransparent;
+    private readonly long[] _gpuSamples = new long[256];   // microseconds
+    private int _gpuSampleCursor;
+    private bool _gpuQueriesInitialized;
+
     public WbDrawDispatcher(
         GL gl,
         Shader shader,
@@ -158,6 +168,16 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
 
         bool diag = string.Equals(Environment.GetEnvironmentVariable("ACDREAM_WB_DIAG"), "1", StringComparison.Ordinal);
 
+        if (diag && !_gpuQueriesInitialized)
+        {
+            _gpuQueryOpaque      = _gl.GenQuery();
+            _gpuQueryTransparent = _gl.GenQuery();
+            _gpuQueriesInitialized = true;
+        }
+
+        // Always run the CPU stopwatch — cheap; only logged under diag.
+        _cpuStopwatch.Restart();
+
         // Camera world-space position for front-to-back sort (perf #2). The view
         // matrix is the inverse of the camera's world transform, so the world
         // translation lives in the inverse's translation row.
@@ -267,6 +287,7 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         // Nothing visible — skip the GL pass entirely.
         if (anyVao == 0)
         {
+            _cpuStopwatch.Stop();
             if (diag) MaybeFlushDiag();
             return;
         }
@@ -276,6 +297,7 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         foreach (var grp in _groups.Values) totalInstances += grp.Matrices.Count;
         if (totalInstances == 0)
         {
+            _cpuStopwatch.Stop();
             if (diag) MaybeFlushDiag();
             return;
         }
@@ -379,12 +401,14 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
             _gl.DepthMask(true);
             _shader.SetInt("uRenderPass", 0);
             _gl.BindBuffer(BufferTargetARB.DrawIndirectBuffer, _indirectBuffer);
+            if (diag && _gpuQueriesInitialized) _gl.BeginQuery(QueryTarget.TimeElapsed, _gpuQueryOpaque);
             _gl.MultiDrawElementsIndirect(
                 PrimitiveType.Triangles,
                 DrawElementsType.UnsignedShort,
                 (void*)0,
                 (uint)_opaqueDrawCount,
                 (uint)DrawCommandStride);
+            if (diag && _gpuQueriesInitialized) _gl.EndQuery(QueryTarget.TimeElapsed);
         }
 
         // ── Phase 8: transparent pass ────────────────────────────────────────
@@ -394,12 +418,14 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
             _gl.BlendFunc(BlendingFactor.SrcAlpha, BlendingFactor.OneMinusSrcAlpha);
             _gl.DepthMask(false);
             _shader.SetInt("uRenderPass", 1);
+            if (diag && _gpuQueriesInitialized) _gl.BeginQuery(QueryTarget.TimeElapsed, _gpuQueryTransparent);
             _gl.MultiDrawElementsIndirect(
                 PrimitiveType.Triangles,
                 DrawElementsType.UnsignedShort,
                 (void*)_transparentByteOffset,
                 (uint)_transparentDrawCount,
                 (uint)DrawCommandStride);
+            if (diag && _gpuQueriesInitialized) _gl.EndQuery(QueryTarget.TimeElapsed);
             _gl.DepthMask(true);
             _gl.Disable(EnableCap.Blend);
         }
@@ -407,9 +433,31 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         _gl.Disable(EnableCap.CullFace);
         _gl.BindVertexArray(0);
 
+        _cpuStopwatch.Stop();
+
         if (diag)
         {
-            _drawsIssued += _opaqueDrawCount + _transparentDrawCount;
+            long cpuUs = _cpuStopwatch.ElapsedTicks * 1_000_000L / System.Diagnostics.Stopwatch.Frequency;
+            _cpuSamples[_cpuSampleCursor] = cpuUs;
+            _cpuSampleCursor = (_cpuSampleCursor + 1) % _cpuSamples.Length;
+
+            // Read GPU samples non-blocking; the result for the previous frame's
+            // queries should be ready by now. If not, drop the sample (don't stall
+            // the CPU waiting for the GPU).
+            if (_gpuQueriesInitialized)
+            {
+                _gl.GetQueryObject(_gpuQueryOpaque, QueryObjectParameterName.ResultAvailable, out int avail);
+                if (avail != 0)
+                {
+                    _gl.GetQueryObject(_gpuQueryOpaque, QueryObjectParameterName.Result, out ulong opaqueNs);
+                    _gl.GetQueryObject(_gpuQueryTransparent, QueryObjectParameterName.Result, out ulong transNs);
+                    long gpuUs = (long)((opaqueNs + transNs) / 1000UL);
+                    _gpuSamples[_gpuSampleCursor] = gpuUs;
+                    _gpuSampleCursor = (_gpuSampleCursor + 1) % _gpuSamples.Length;
+                }
+            }
+
+            _drawsIssued     += _opaqueDrawCount + _transparentDrawCount;
             _instancesIssued += totalInstances;
             MaybeFlushDiag();
         }
@@ -437,13 +485,41 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         long now = Environment.TickCount64;
         if (now - _lastLogTick > 5000)
         {
+            long cpuMed = MedianMicros(_cpuSamples);
+            long cpuP95 = Percentile95Micros(_cpuSamples);
+            long gpuMed = MedianMicros(_gpuSamples);
+            long gpuP95 = Percentile95Micros(_gpuSamples);
             Console.WriteLine(
-                $"[WB-DIAG] entSeen={_entitiesSeen} entDrawn={_entitiesDrawn} meshMissing={_meshesMissing} drawsIssued={_drawsIssued} instances={_instancesIssued} groups={_groups.Count}");
+                $"[WB-DIAG] entSeen={_entitiesSeen} entDrawn={_entitiesDrawn} meshMissing={_meshesMissing} drawsIssued={_drawsIssued} instances={_instancesIssued} groups={_groups.Count} " +
+                $"cpu_us={cpuMed}m/{cpuP95}p95 gpu_us={gpuMed}m/{gpuP95}p95");
             _entitiesSeen = _entitiesDrawn = _meshesMissing = _drawsIssued = _instancesIssued = 0;
             _lastLogTick = now;
+            // Don't reset the sample buffers — they're a moving window of the
+            // last 256 frames; clearing per 5s flush would lose recent history.
         }
     }
 
+    private static long MedianMicros(long[] samples)
+    {
+        var copy = (long[])samples.Clone();
+        Array.Sort(copy);
+        int nz = 0;
+        foreach (var v in copy) if (v > 0) nz++;
+        if (nz == 0) return 0;
+        return copy[copy.Length - nz / 2];
+    }
+
+    private static long Percentile95Micros(long[] samples)
+    {
+        var copy = (long[])samples.Clone();
+        Array.Sort(copy);
+        int nz = 0;
+        foreach (var v in copy) if (v > 0) nz++;
+        if (nz == 0) return 0;
+        int idx = copy.Length - 1 - (int)(nz * 0.05);
+        return copy[idx];
+    }
+
     private void ClassifyBatches(
         ObjectRenderData renderData,
         ulong gfxObjId,
@@ -538,6 +614,11 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         _gl.DeleteBuffer(_instanceSsbo);
         _gl.DeleteBuffer(_batchSsbo);
         _gl.DeleteBuffer(_indirectBuffer);
+        if (_gpuQueriesInitialized)
+        {
+            _gl.DeleteQuery(_gpuQueryOpaque);
+            _gl.DeleteQuery(_gpuQueryTransparent);
+        }
     }
 
     // ── Public types + helpers for BuildIndirectArrays (Task 9) ─────────────