Curves: Add sculpt selection overlay

This commit adds visualization to the selection in curves sculpt mode.
Previously it was only possible to see the selection when it was
connected to a material.

In order to obstruct the users vision as little as possible, the
selected areas of the curve are left as is, but a dark overlay
is drawn over unselected areas.

To make it work, the overlay requests the selection attribute and then
ensures that the evaluation is complete for curves. Then it retrieves
the evaluated selection GPU texture and passes that to the shader.
This reuses the existing generic attribute extraction system because
there currently wouldn't be any benefits to dealing with selection
separately, and because it avoids duplication of the logic that
extracts attributes from curves and evaluates them if necessary.

Differential Revision: https://developer.blender.org/D15219

1 files changed, 10 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_cache_impl.h b/source/blender/draw/intern/draw_cache_impl.h
index 4fa5813d476..91dbef8d7b1 100644
--- a/source/blender/draw/intern/draw_cache_impl.h
+++ b/source/blender/draw/intern/draw_cache_impl.h
@@ -161,6 +161,16 @@ struct GPUBatch *DRW_lattice_batch_cache_get_edit_verts(struct Lattice *lt);
 
 int DRW_curves_material_count_get(struct Curves *curves);
 
+/**
+ * Provide GPU access to a specific evaluated attribute on curves.
+ *
+ * \return A pointer to location where the texture will be
+ * stored, which will be filled by #DRW_shgroup_curves_create_sub.
+ */
+struct GPUTexture **DRW_curves_texture_for_evaluated_attribute(struct Curves *curves,
+                                                               const char *name,
+                                                               bool *r_is_point_domain);
+
 struct GPUBatch *DRW_curves_batch_cache_get_edit_points(struct Curves *curves);
 
 void DRW_curves_batch_cache_create_requested(struct Object *ob);