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, 11 insertions, 0 deletions

diff --git a/source/blender/gpu/GPU_material.h b/source/blender/gpu/GPU_material.h
index c0633f0323d..3ca465fa57a 100644
--- a/source/blender/gpu/GPU_material.h
+++ b/source/blender/gpu/GPU_material.h
@@ -131,6 +131,11 @@ typedef void (*GPUCodegenCallbackFn)(void *thunk, GPUMaterial *mat, GPUCodegenOu
 GPUNodeLink *GPU_constant(const float *num);
 GPUNodeLink *GPU_uniform(const float *num);
 GPUNodeLink *GPU_attribute(GPUMaterial *mat, eCustomDataType type, const char *name);
+/**
+ * Add a GPU attribute that refers to the default color attribute on a geometry.
+ * The name, type, and domain are unknown and do not depend on the material.
+ */
+GPUNodeLink *GPU_attribute_default_color(GPUMaterial *mat);
 GPUNodeLink *GPU_attribute_with_default(GPUMaterial *mat,
                                         eCustomDataType type,
                                         const char *name,
@@ -266,6 +271,12 @@ typedef struct GPUMaterialAttribute {
   eGPUDefaultValue default_value; /* Only for volumes attributes. */
   int id;
   int users;
+  /**
+   * If true, the corresponding attribute is the specified default color attribute on the mesh,
+   * if it exists. In that case the type and name data can vary per geometry, so it will not be
+   * valid here.
+   */
+  bool is_default_color;
 } GPUMaterialAttribute;
 
 typedef struct GPUMaterialTexture {