Fix flw_vertexId

- Need to subtract base instance from gl instance ID

Author: Jozufozu

common/src/backend/java/dev/engine_room/flywheel/backend/engine/instancing/InstancedDrawManager.java

@@ -160,7 +160,7 @@ private void submitDraws() {
 
 			uploadMaterialUniform(program, material);
 
-			program.setUInt("_flw_vertexOffset", drawCall.mesh()
+			program.setUInt("_flw_baseVertex", drawCall.mesh()
 					.baseVertex());
 
 			MaterialRenderState.setup(material);
@@ -184,7 +184,7 @@ private void submitOitDraws(PipelineCompiler.OitMode mode) {
 
 			uploadMaterialUniform(program, material);
 
-			program.setUInt("_flw_vertexOffset", drawCall.mesh()
+			program.setUInt("_flw_baseVertex", drawCall.mesh()
 					.baseVertex());
 
 			MaterialRenderState.setupOit(material);

common/src/backend/resources/assets/flywheel/flywheel/internal/api_impl.vert

@@ -13,4 +13,4 @@ out float flw_distance;
 
 FlwMaterial flw_material;
 
-#define flw_vertexId gl_VertexID
+uint flw_vertexId;

common/src/backend/resources/assets/flywheel/flywheel/internal/common.vert

@@ -75,7 +75,9 @@ mat3 _flw_normalMatrix;
 flat out uvec2 _flw_ids;
 #endif
 
-void _flw_main(in FlwInstance instance, in uint stableInstanceID, in uint modelID) {
+void _flw_main(in FlwInstance instance, in uint stableInstanceID, in uint baseVertex) {
+    flw_vertexId = gl_VertexID - baseVertex;
+
     _flw_layoutVertex();
     flw_instanceVertex(instance);
     flw_materialVertex();
@@ -96,6 +98,6 @@ void _flw_main(in FlwInstance instance, in uint stableInstanceID, in uint modelI
     gl_Position = flw_viewProjection * flw_vertexPos;
 
     #ifdef _FLW_DEBUG
-    _flw_ids = uvec2(stableInstanceID, modelID);
+    _flw_ids = uvec2(stableInstanceID, baseVertex);
     #endif
 }

common/src/backend/resources/assets/flywheel/flywheel/internal/instancing/main.vert

@@ -10,7 +10,7 @@ uniform mat4 _flw_modelMatrixUniform;
 uniform mat3 _flw_normalMatrixUniform;
 #endif
 
-uniform uint _flw_vertexOffset;
+uniform uint _flw_baseVertex;
 
 void main() {
     _flw_unpackMaterialProperties(_flw_packedMaterial.y, flw_material);
@@ -22,5 +22,5 @@ void main() {
     _flw_normalMatrix = _flw_normalMatrixUniform;
     #endif
 
-    _flw_main(instance, uint(gl_InstanceID), _flw_vertexOffset);
+    _flw_main(instance, uint(gl_InstanceID), _flw_baseVertex);
 }

docs/flywheel/api/snippets/vertex.glsl

@@ -8,6 +8,9 @@ ivec2 flw_vertexOverlay;
 vec2 flw_vertexLight;
 vec3 flw_vertexNormal;
 
+// The index of the current vertex in the mesh that is being drawn.
+/*const*/ uint flw_vertexId;
+
 /*const*/ FlwMaterial flw_material;
 
 // To be implemented by the instance shader.