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

2 files changed, 3 insertions, 16 deletions

diff --git a/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_uv.cc b/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_uv.cc
index 4532f3c3710..5fb4b401ae3 100644
--- a/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_uv.cc
+++ b/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_uv.cc
@@ -44,14 +44,11 @@ static bool mesh_extract_uv_format_init(GPUVertFormat *format,
 
       GPU_vertformat_safe_attr_name(layer_name, attr_safe_name, GPU_MAX_SAFE_ATTR_NAME);
       /* UV layer name. */
-      BLI_snprintf(attr_name, sizeof(attr_name), "u%s", attr_safe_name);
-      GPU_vertformat_attr_add(format, attr_name, GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
-      /* Auto layer name. */
       BLI_snprintf(attr_name, sizeof(attr_name), "a%s", attr_safe_name);
-      GPU_vertformat_alias_add(format, attr_name);
+      GPU_vertformat_attr_add(format, attr_name, GPU_COMP_F32, 2, GPU_FETCH_FLOAT);
       /* Active render layer name. */
       if (i == CustomData_get_render_layer(cd_ldata, CD_MLOOPUV)) {
-        GPU_vertformat_alias_add(format, "u");
+        GPU_vertformat_alias_add(format, "a");
       }
       /* Active display layer name. */
       if (i == CustomData_get_active_layer(cd_ldata, CD_MLOOPUV)) {
diff --git a/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_vcol.cc b/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_vcol.cc
index 4cb68cad66c..e5dd025787d 100644
--- a/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_vcol.cc
+++ b/source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_vcol.cc
@@ -90,7 +90,7 @@ static void init_vcol_format(GPUVertFormat *format,
     GPU_vertformat_safe_attr_name(ref.layer->name, attr_safe_name, GPU_MAX_SAFE_ATTR_NAME);
 
     /* VCol layer name. */
-    BLI_snprintf(attr_name, sizeof(attr_name), "c%s", attr_safe_name);
+    BLI_snprintf(attr_name, sizeof(attr_name), "a%s", attr_safe_name);
     GPU_vertformat_attr_add(format, attr_name, GPU_COMP_U16, 4, GPU_FETCH_INT_TO_FLOAT_UNIT);
 
     /* Active layer name. */
@@ -102,16 +102,6 @@ static void init_vcol_format(GPUVertFormat *format,
     if (ref.layer == render) {
       GPU_vertformat_alias_add(format, "c");
     }
-
-    /* Gather number of auto layers. */
-    /* We only do `vcols` that are not overridden by `uvs`. */
-    bool bad = ref.domain == ATTR_DOMAIN_CORNER;
-    bad = bad && CustomData_get_named_layer_index(cd_ldata, CD_MLOOPUV, ref.layer->name) != -1;
-
-    if (!bad) {
-      BLI_snprintf(attr_name, sizeof(attr_name), "a%s", attr_safe_name);
-      GPU_vertformat_alias_add(format, attr_name);
-    }
   }
 }