From 336ad3444405c26f5d96bc00918084d5a5af8a9c Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Sat, 9 May 2026 09:36:13 +0200
Subject: [PATCH] =?UTF-8?q?chore(N.5b):=20TEMPORARY=20perf=20benchmark=20t?=
 =?UTF-8?q?oggle=20for=20legacy=E2=86=94modern=20terrain?=
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Adds an ACDREAM_LEGACY_TERRAIN=1 env var that routes Draw through the
legacy TerrainChunkRenderer instead of the new TerrainModernRenderer.
Both renderers are constructed and fed AddLandblock/RemoveLandblock so
they stay in sync; only one is drawn per frame. The [TERRAIN-DIAG]
log line is labeled /modern or /legacy so the user can tell which
numbers they're capturing.

Removed in Task 9 along with TerrainChunkRenderer.cs, terrain.vert,
and terrain.frag.

Usage:
  \$env:ACDREAM_LEGACY_TERRAIN = "1"   # legacy mode
  \$env:ACDREAM_LEGACY_TERRAIN = \$null # modern mode (default)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 src/AcDream.App/Rendering/GameWindow.cs | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index f8edcaa..f34fb77 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -19,6 +19,12 @@ public sealed class GameWindow : IDisposable
     private GL? _gl;
     private IInputContext? _input;
     private TerrainModernRenderer? _terrain;
+    // Phase N.5b benchmark toggle (TEMPORARY — removed in Task 9 along with TerrainChunkRenderer):
+    // when ACDREAM_LEGACY_TERRAIN=1, route Draw through the legacy renderer
+    // for direct perf comparison. Both renderers are constructed and fed
+    // AddLandblock/RemoveLandblock; only one is drawn per frame.
+    private TerrainChunkRenderer? _terrainLegacy;
+    private bool _useLegacyTerrain;
     private Shader? _shader;
     /// <summary>Phase N.5b: terrain_modern.vert/.frag program. Owned by
     /// <see cref="_terrain"/> at draw time but allocated + disposed here. Lives
@@ -1445,6 +1451,10 @@ public sealed class GameWindow : IDisposable
 
         _terrain = new TerrainModernRenderer(_gl, _bindlessSupport, _terrainModernShader!, terrainAtlas);
 
+        // Phase N.5b benchmark toggle (TEMPORARY — see field declaration).
+        _useLegacyTerrain = Environment.GetEnvironmentVariable("ACDREAM_LEGACY_TERRAIN") == "1";
+        _terrainLegacy = new TerrainChunkRenderer(_gl, _shader!, terrainAtlas);
+
         int centerX = (int)((centerLandblockId >> 24) & 0xFFu);
         int centerY = (int)((centerLandblockId >> 16) & 0xFFu);
 
@@ -1602,6 +1612,7 @@ public sealed class GameWindow : IDisposable
                         _lightingSink.UnregisterOwner(ent.Id);
                 }
                 _terrain?.RemoveLandblock(id);
+                _terrainLegacy?.RemoveLandblock(id);   // Phase N.5b benchmark toggle (TEMPORARY).
                 _physicsEngine.RemoveLandblock(id);
                 _cellVisibility.RemoveLandblock((id >> 16) & 0xFFFFu);
             });
@@ -5122,6 +5133,7 @@ public sealed class GameWindow : IDisposable
         var meshData = AcDream.Core.Terrain.LandblockMesh.Build(
             lb.Heightmap, lbXu, lbYu, _heightTable, _blendCtx, _surfaceCache);
         _terrain.AddLandblock(lb.LandblockId, meshData, origin);
+        _terrainLegacy?.AddLandblock(lb.LandblockId, meshData, origin);   // Phase N.5b benchmark toggle (TEMPORARY).
 
         // Step 4: drain pending LoadedCells from the worker thread.
         while (_pendingCells.TryTake(out var cell))
@@ -6346,7 +6358,11 @@ public sealed class GameWindow : IDisposable
             // (gated on ACDREAM_WB_DIAG=1, same env var as [WB-DIAG]). Stopwatch
             // is cheap; only the periodic Console.WriteLine is gated.
             _terrainCpuStopwatch.Restart();
-            _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+            // Phase N.5b benchmark toggle (TEMPORARY): pick renderer per ACDREAM_LEGACY_TERRAIN.
+            if (_useLegacyTerrain)
+                _terrainLegacy?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+            else
+                _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
             _terrainCpuStopwatch.Stop();
             _terrainCpuSamples[_terrainCpuSampleCursor] = (long)(_terrainCpuStopwatch.Elapsed.TotalMicroseconds);
             _terrainCpuSampleCursor = (_terrainCpuSampleCursor + 1) % _terrainCpuSamples.Length;
@@ -8765,7 +8781,7 @@ public sealed class GameWindow : IDisposable
         long cpuMedUs = TerrainDiagMedianMicros(_terrainCpuSamples);
         long cpuP95Us = TerrainDiagPercentile95Micros(_terrainCpuSamples);
         Console.WriteLine(
-            $"[TERRAIN-DIAG] cpu_ms={cpuMedUs / 1000.0:F2}/{cpuP95Us / 1000.0:F2}  " +
+            $"[TERRAIN-DIAG{(_useLegacyTerrain ? "/legacy" : "/modern")}] cpu_ms={cpuMedUs / 1000.0:F2}/{cpuP95Us / 1000.0:F2}  " +
             $"draws={_terrain?.VisibleSlots ?? 0}/frame  " +
             $"visible={_terrain?.VisibleSlots ?? 0}  " +
             $"loaded={_terrain?.LoadedSlots ?? 0}  " +
@@ -8813,6 +8829,7 @@ public sealed class GameWindow : IDisposable
 
         _meshShader?.Dispose();
         _terrain?.Dispose();
+        _terrainLegacy?.Dispose();   // Phase N.5b benchmark toggle (TEMPORARY).
         _shader?.Dispose();
         _terrainModernShader?.Dispose();
         _sceneLightingUbo?.Dispose();