initial code

Still have to figure out some naming, but seems to work in my test cases.

This also changes the overlay in edit mode so that it takes the cage into account.

Differential Revision: https://developer.blender.org/D17154

@@ -343,0 +365,4 @@
+  /* Create cage curves geometry for drawing. */
+  if (generate_cage) {
+    const blender::bke::CurvesGeometry &curves_orig = curves_id_orig.geometry.wrap();
+    Curves *curves_id_cage = blender::bke::curves_new_nomain(curves_id_orig.geometry.point_num,

@@ -361,0 +379,4 @@
+  GPU_vertbuf_data_alloc(&point_color_buf, curves.points_num());
+  blender::uchar4 *data = static_cast<blender::uchar4 *>(GPU_vertbuf_get_data(&point_color_buf));
+
+  const blender::VArraySpan<float> selection = curves.attributes().lookup_or_default<float>(

@@ -172,2 +172,4 @@
   struct Mesh *editmesh_eval_cage;
 
+  /** Evaluated curve cage in edit and sculpt mode. */
+  struct Curves *editcurves_eval_cage;

@@ -4717,0 +4717,4 @@
+  prop = RNA_def_property(srna, "sculpt_curves_cage", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "overlay.flag", V3D_OVERLAY_SCULPT_CURVES_CAGE);
+  RNA_def_property_ui_text(
+      prop, "Sculpt Curves Cage", "Show points that are currently being edited");

@@ -8,3 +8,3 @@
   gl_Position = point_world_to_ndc(world_pos);
 
-  finalColor = mix(colorWire, colorVertexSelect, color);
+  finalColor = mix(colorWire, colorVertexSelect, selection);

@@ -293,1 +292,3 @@
-  DEG_id_tag_update(&ob->id, ID_RECALC_COPY_ON_WRITE);
+  /* Necessary to change the object mode on the evaluated object and to evaluate the cage that is
+   * edited. */
+  DEG_id_tag_update(&ob->id, ID_RECALC_COPY_ON_WRITE | ID_RECALC_GEOMETRY);