Merge pull request #79660 from bitsawer/fix_opengl_multimesh

Fix GLES3 multimesh rendering when using colors or custom data

drivers/gles3/storage/mesh_storage.cpp

@@ -1284,13 +1284,17 @@ void MeshStorage::multimesh_allocate_data(RID p_multimesh, int p_instances, RS::
 		multimesh->data_cache_used_dirty_regions = 0;
 	}
 
+	// If we have either color or custom data, reserve space for both to make data handling logic simpler.
+	// This way we can always treat them both as a single, compressed uvec4.
+	int color_and_custom_strides = (p_use_colors || p_use_custom_data) ? 2 : 0;
+
 	multimesh->instances = p_instances;
 	multimesh->xform_format = p_transform_format;
 	multimesh->uses_colors = p_use_colors;
 	multimesh->color_offset_cache = p_transform_format == RS::MULTIMESH_TRANSFORM_2D ? 8 : 12;
 	multimesh->uses_custom_data = p_use_custom_data;
-	multimesh->custom_data_offset_cache = multimesh->color_offset_cache + (p_use_colors ? 2 : 0);
-	multimesh->stride_cache = multimesh->custom_data_offset_cache + (p_use_custom_data ? 2 : 0);
+	multimesh->custom_data_offset_cache = multimesh->color_offset_cache + color_and_custom_strides;
+	multimesh->stride_cache = multimesh->custom_data_offset_cache + color_and_custom_strides;
 	multimesh->buffer_set = false;
 
 	multimesh->data_cache = Vector<float>();