Geometry Nodes: improve support for Color attributes

* Add typed attribute accessors for color attributes.
* Support implicit conversions between colors and floats.

source/blender/blenkernel/BKE_attribute_access.hh

@@ -23,6 +23,7 @@
 
 #include "BKE_attribute.h"
 
+#include "BLI_color.hh"
 #include "BLI_float3.hh"
 
 struct Mesh;
@@ -267,10 +268,9 @@ template<typename T> class TypedWriteAttribute {
 
 using FloatReadAttribute = TypedReadAttribute<float>;
 using Float3ReadAttribute = TypedReadAttribute<float3>;
+using Color4fReadAttribute = TypedReadAttribute<Color4f>;
 using FloatWriteAttribute = TypedWriteAttribute<float>;
 using Float3WriteAttribute = TypedWriteAttribute<float3>;
-
-const CPPType *custom_data_type_to_cpp_type(const CustomDataType type);
-CustomDataType cpp_type_to_custom_data_type(const CPPType &type);
+using Color4fWriteAttribute = TypedWriteAttribute<Color4f>;
 
 }  // namespace blender::bke

source/blender/nodes/NOD_geometry_exec.hh

@@ -26,6 +26,8 @@
 
 namespace blender::nodes {
 
+using bke::Color4fReadAttribute;
+using bke::Color4fWriteAttribute;
 using bke::Float3ReadAttribute;
 using bke::Float3WriteAttribute;
 using bke::FloatReadAttribute;

source/blender/nodes/intern/node_tree_multi_function.cc

@@ -204,6 +204,10 @@ static DataTypeConversions create_implicit_conversions()
       conversions, "float3 to Color4f", [](float3 a) { return Color4f(a.x, a.y, a.z, 1.0f); });
   add_implicit_conversion<Color4f, float3>(
       conversions, "Color4f to float3", [](Color4f a) { return float3(a.r, a.g, a.b); });
+  add_implicit_conversion<float, Color4f>(
+      conversions, "float to Color4f", [](float a) { return Color4f(a, a, a, 1.0f); });
+  add_implicit_conversion<Color4f, float>(
+      conversions, "Color4f to float", [](Color4f a) { return rgb_to_grayscale(a); });
   return conversions;
 }