add code notes on REDEngine, add thoughts

DsoTsin · DsoTsin · commit 9682aad54cd6 · 2024-04-12T16:11:49.000+08:00
diff --git a/12.red_engine_notes/REDEngineGI.md b/12.red_engine_notes/REDEngineGI.md
@@ -0,0 +1,56 @@
+# REDEngine的GI
+
+相关源码文件
+
+* giProbeBakingUtility.cpp **[backendPipeline]**
+    * GI::RenderProbes
+    * ProbeBakeGeneratorState::ProcessProbeData
+        * 烘焙GI Surfel
+        * 一个启发是近距离的Surfel数据可以通过多帧GBuffer来生成，而不是通过Voxelization，这样能更高保真度的保存数据，这个Surfel数据的保存可以通过Spatial Hash Grid保存，类似的实现在AMD BrixelGI里有所提及；HSGI[TX]则将Voxelization生成的world space surfel数据作为GI场景表达的一个补充，当然也可以考虑多帧GBuffer生成surfel voxel修正漏光
+    * ScheduleGIGenerate
+        * "Detect Empty Sectors ( Only Terrain and Roads )"
+        * "Create Proxies for the scene"
+        * "Create Scene and Add Proxies"
+        * "GI Probes placement"
+            * Max probes per sector
+        * "Initial tetrahedralization of probes"
+        * "Render GI Probes"
+        * "Clean After GI Probes"
+        * "Merge TetStructures"
+        * "Process GI Bricks"
+        * "Generate DepthMap"
+        * "RayTrace Surfel-Probe"
+            * Collect surfels
+        * "Generate Save Data.. Save header"
+        * "Generate Save Data.. Processing Surfels"
+            * Using HilbertID/Morton Code
+                ```C
+                Uint32 HilbertID( Uint32 x, Uint32 y, Uint32 z )
+                {
+                #define SPLIT_BITS(b)					\
+                    b = (b | (b << 16)) & 0x030000FF;	\
+                    b = (b | (b << 8)) & 0x0300F00F;	\
+                    b = (b | (b << 4)) & 0x030C30C3;	\
+                    b = (b | (b << 2)) & 0x09249249;	
+                    SPLIT_BITS( x );
+                    SPLIT_BITS( y );
+                    SPLIT_BITS( z );
+                #undef SPLIT_BITS
+                    return x | (y<<1) | (z<<2);
+                }
+                ```
+        * "Generate Save Data.. Post RayCast"
+        * "Save Resources"
+        * "Clean up"
+        * UE里去实现这个过程利用GPU Lightmass会比较合适
+            * GPULightmass有完整的GPU Scene、材质信息
+* giProbeDistributionGenerator.cpp **[backendPipeline]**
+    * ProbeDistribuitionGenerator::Generate `"Distribute probes"`
+        * runtimeSystemGI.cpp **[backendPrecomputedLight]**
+            * GI::CProbeSpawner::PopulateProbeData
+                * 先生成SDF数据
+                * 然后根据摆放的GIVolume在Volume内的Mesh按密度控制沿着表面布置Probe
+* giProbeSectorsGenerator.cpp
+    * ProbeSectorsGenerator
+
+
