Refactor: Extract color attributes as generic attributes

Previously there was a special extraction process for "vertex colors"
that copied the color data to the GPU with a special format. Instead,
this patch replaces this with use of the generic attribute extraction.
This reduces the number of code paths, allowing easier optimization
in the future.

To make it possible to use the generic extraction system for attributes
but also assign aliases for use by shaders, some changes are necessary.
First, the GPU material attribute can now store whether it actually refers
to the default color attribute, rather than a specific name. This replaces
the hack to use `CD_MCOL` in the color attribute shader node. Second,
the extraction code checks the names against the default and active
names and assigns aliases if the request corresponds to a special active
attribute. Finally, support for byte color attributes was added to the
generic attribute extraction.

Differential Revision: https://developer.blender.org/D15205

1 files changed, 3 insertions, 4 deletions

diff --git a/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc b/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc
index 830f02d8df1..c636cc976e6 100644
--- a/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc
+++ b/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc
@@ -42,9 +42,8 @@ static int node_shader_gpu_vertex_color(GPUMaterial *mat,
                                         GPUNodeStack *out)
 {
   NodeShaderVertexColor *vertexColor = (NodeShaderVertexColor *)node->storage;
-  /* NOTE: using CD_AUTO_FROM_NAME instead of CD_MCOL or CD_PROP_COLOR for named attributes
-   * as geometry nodes may overwrite data which will also change the eCustomDataType.
-   * This will also make EEVEE and Cycles
+  /* NOTE: Using #CD_AUTO_FROM_NAME is necessary because there are multiple color attribute types,
+   * and the type may change during evaluation anyway. This will also make EEVEE and Cycles
    * consistent. See T93179. */
 
   GPUNodeLink *vertexColorLink;
@@ -53,7 +52,7 @@ static int node_shader_gpu_vertex_color(GPUMaterial *mat,
     vertexColorLink = GPU_attribute(mat, CD_AUTO_FROM_NAME, vertexColor->layer_name);
   }
   else { /* Fall back on active render color attribute. */
-    vertexColorLink = GPU_attribute(mat, CD_MCOL, vertexColor->layer_name);
+    vertexColorLink = GPU_attribute_default_color(mat);
   }
 
   return GPU_stack_link(mat, node, "node_vertex_color", in, out, vertexColorLink);