Curves: Add surface UV map name property

In the latest discussions about curves/hair mesh attachement
information (T95776), it was decided to use UV coordinates to
store where on the mesh each root is. For that, we have to specify
which of the UV map attributes to use for UV lookups.

This property isn't used yet, but it will be shortly when refactoring
the attachement information in the add brush and the to particle
system conversion.

Differential Revision: https://developer.blender.org/D15115

release/scripts/startup/bl_ui/properties_data_curves.py

@@ -44,6 +44,7 @@ class DATA_PT_curves_surface(DataButtonsPanel, Panel):
         layout.use_property_split = True
 
         layout.prop(ob.data, "surface")
+        layout.prop(ob.data, "surface_uv_map", text="UV Map")
 
 
 class CURVES_MT_add_attribute(Menu):

source/blender/blenkernel/intern/curves.cc

@@ -89,6 +89,10 @@ static void curves_copy_data(Main *UNUSED(bmain), ID *id_dst, const ID *id_src,
 
   dst.curve_offsets = static_cast<int *>(MEM_dupallocN(src.curve_offsets));
 
+  if (curves_src->surface_uv_map != nullptr) {
+    curves_dst->surface_uv_map = BLI_strdup(curves_src->surface_uv_map);
+  }
+
   dst.runtime = MEM_new<bke::CurvesGeometryRuntime>(__func__);
 
   dst.runtime->type_counts = src.runtime->type_counts;
@@ -108,6 +112,7 @@ static void curves_free_data(ID *id)
   BKE_curves_batch_cache_free(curves);
 
   MEM_SAFE_FREE(curves->mat);
+  MEM_SAFE_FREE(curves->surface_uv_map);
 }
 
 static void curves_foreach_id(ID *id, LibraryForeachIDData *data)
@@ -148,6 +153,8 @@ static void curves_blend_write(BlendWriter *writer, ID *id, const void *id_addre
 
   BLO_write_int32_array(writer, curves->geometry.curve_num + 1, curves->geometry.curve_offsets);
 
+  BLO_write_string(writer, curves->surface_uv_map);
+
   BLO_write_pointer_array(writer, curves->totcol, curves->mat);
   if (curves->adt) {
     BKE_animdata_blend_write(writer, curves->adt);
@@ -167,6 +174,8 @@ static void curves_blend_read_data(BlendDataReader *reader, ID *id)
 
   BLO_read_int32_array(reader, curves->geometry.curve_num + 1, &curves->geometry.curve_offsets);
 
+  BLO_read_data_address(reader, &curves->surface_uv_map);
+
   curves->geometry.runtime = MEM_new<blender::bke::CurvesGeometryRuntime>(__func__);
 
   /* Recalculate curve type count cache that isn't saved in files. */

source/blender/makesdna/DNA_curves_types.h

@@ -157,6 +157,13 @@ typedef struct Curves {
    */
   struct Object *surface;
 
+  /**
+   * The name of the attribute on the surface #Mesh used to give meaning to the UV attachment
+   * coordinates stored on each curve. Expected to be a 2D vector attribute on the face corner
+   * domain.
+   */
+  char *surface_uv_map;
+
   /* Draw Cache. */
   void *batch_cache;
 } Curves;

source/blender/makesrna/intern/rna_curves.c

@@ -292,6 +292,14 @@ static void rna_def_curves(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Surface", "Mesh object that the curves can be attached to");
   RNA_def_property_update(prop, NC_OBJECT | ND_DRAW, NULL);
 
+  prop = RNA_def_property(srna, "surface_uv_map", PROP_STRING, PROP_NONE);
+  RNA_def_property_string_sdna(prop, NULL, "surface_uv_map");
+  RNA_def_property_ui_text(prop,
+                           "Surface UV Map",
+                           "The name of the attribute on the surface mesh used to define the "
+                           "attachment of each curve");
+  RNA_def_property_update(prop, 0, "rna_Curves_update_draw");
+
   /* Symmetry. */
   prop = RNA_def_property(srna, "use_mirror_x", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "symmetry", CURVES_SYMMETRY_X);