Fix T93179: geonodes UVs and Vertex colors do not work in EEVEE

Overwriting UV map or vertex color data in Geometry nodes will move the
layers to another CustomData channel, and as such, will make attribute
lookup fail from the UVMap and Vertex Color nodes in EEVEE as the
CustomDataType will also be modified (i.e. no longer `CD_MTFACE` or
`CD_MCOL`).

As discussed in T93179, the solution is to use `CD_PROP_AUTO_FROM_NAME`
so that the render engine is able to find the attributes. This also makes
EEVEE emulate Cycles behaviour in this regard. `attr_load_uv` and
`attr_load_color` are also removed in favor of the generic attribute
API in the various GLSL shaders.

Although `CD_PROP_AUTO_FROM_NAME` is now used even for UV maps, the
active UV map is still used in case the attribute name is empty, to
preserve the old behavior.

Differential Revision: https://developer.blender.org/D13730

1 files changed, 4 insertions, 1 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 22b0744333d..a2a9aa9ad91 100644
--- a/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc
+++ b/source/blender/nodes/shader/nodes/node_shader_vertex_color.cc
@@ -42,7 +42,10 @@ static int node_shader_gpu_vertex_color(GPUMaterial *mat,
                                         GPUNodeStack *out)
 {
   NodeShaderVertexColor *vertexColor = (NodeShaderVertexColor *)node->storage;
-  GPUNodeLink *vertexColorLink = GPU_attribute(mat, CD_PROP_COLOR, vertexColor->layer_name);
+  /* NOTE: using CD_AUTO_FROM_NAME instead of CD_MCOL or CD_PROP_COLOR as geometry nodes may
+   * overwrite data which will also change the CustomDataType. This will also make EEVEE and Cycles
+   * consistent. See T93179. */
+  GPUNodeLink *vertexColorLink = GPU_attribute(mat, CD_AUTO_FROM_NAME, vertexColor->layer_name);
   return GPU_stack_link(mat, node, "node_vertex_color", in, out, vertexColorLink);
 }