Curves: new Add brush

This adds a new Add brush for the new curves object type in sculpt mode.
The brush is used to insert new curves (typically hair) on the surface object.

Supported features:
* Add single curve exactly at the cursor position when `Add Amount` is 1.
* Front faces only.
* Independent interpolate shape and interpolate length settings.
* Smooth and flat shading affects curve shape interpolation.
* Spherical and projection brush.

This also adds the `surface_triangle_index` and `surface_triangle_coordinate`
attributes. Those store information about what position on the surface each
added curve is attached to:
* `surface_triangle_index` (`int`): Index of the internal triangle that a curve
  is attached to. `-1` when the curve is not attached to the surface.
* `surface_triangle_coordinate` (`float2`): First two numbers of a barycentric
  coordinate that reference a specific position within the triangle.

Ref T96444.

Differential Revision: https://developer.blender.org/D14340

2 files changed, 38 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_brush.c b/source/blender/makesrna/intern/rna_brush.c
index ee4718aff03..c86a852b0ea 100644
--- a/source/blender/makesrna/intern/rna_brush.c
+++ b/source/blender/makesrna/intern/rna_brush.c
@@ -247,6 +247,7 @@ const EnumPropertyItem rna_enum_brush_curves_sculpt_tool_items[] = {
     {CURVES_SCULPT_TOOL_COMB, "COMB", ICON_NONE, "Comb", ""},
     {CURVES_SCULPT_TOOL_DELETE, "DELETE", ICON_NONE, "Delete", ""},
     {CURVES_SCULPT_TOOL_SNAKE_HOOK, "SNAKE_HOOK", ICON_NONE, "Snake Hook", ""},
+    {CURVES_SCULPT_TOOL_ADD, "ADD", ICON_NONE, "Add", ""},
     {CURVES_SCULPT_TOOL_TEST1, "TEST1", ICON_NONE, "Test 1", ""},
     {CURVES_SCULPT_TOOL_TEST2, "TEST2", ICON_NONE, "Test 2", ""},
     {0, NULL, 0, NULL, NULL},
@@ -1913,6 +1914,20 @@ static void rna_def_gpencil_options(BlenderRNA *brna)
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
 }
 
+static void rna_def_curves_sculpt_options(BlenderRNA *brna)
+{
+  StructRNA *srna;
+  PropertyRNA *prop;
+
+  srna = RNA_def_struct(brna, "BrushCurvesSculptSettings", NULL);
+  RNA_def_struct_sdna(srna, "BrushCurvesSculptSettings");
+  RNA_def_struct_ui_text(srna, "Curves Sculpt Brush Settings", "");
+
+  prop = RNA_def_property(srna, "add_amount", PROP_INT, PROP_NONE);
+  RNA_def_property_range(prop, 1, INT32_MAX);
+  RNA_def_property_ui_text(prop, "Add Amount", "Number of curves added by the Add brush");
+}
+
 static void rna_def_brush(BlenderRNA *brna)
 {
   StructRNA *srna;
@@ -3491,6 +3506,11 @@ static void rna_def_brush(BlenderRNA *brna)
   RNA_def_property_pointer_sdna(prop, NULL, "gpencil_settings");
   RNA_def_property_clear_flag(prop, PROP_EDITABLE);
   RNA_def_property_ui_text(prop, "Gpencil Settings", "");
+
+  prop = RNA_def_property(srna, "curves_sculpt_settings", PROP_POINTER, PROP_NONE);
+  RNA_def_property_struct_type(prop, "BrushCurvesSculptSettings");
+  RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+  RNA_def_property_ui_text(prop, "Curves Sculpt Settings", "");
 }
 
 /**
@@ -3577,6 +3597,7 @@ void RNA_def_brush(BlenderRNA *brna)
   rna_def_vertex_paint_capabilities(brna);
   rna_def_weight_paint_capabilities(brna);
   rna_def_gpencil_options(brna);
+  rna_def_curves_sculpt_options(brna);
   rna_def_brush_texture_slot(brna);
   rna_def_operator_stroke_element(brna);
 }
diff --git a/source/blender/makesrna/intern/rna_sculpt_paint.c b/source/blender/makesrna/intern/rna_sculpt_paint.c
index 40f3d79b363..97e1f325816 100644
--- a/source/blender/makesrna/intern/rna_sculpt_paint.c
+++ b/source/blender/makesrna/intern/rna_sculpt_paint.c
@@ -1518,6 +1518,23 @@ static void rna_def_curves_sculpt(BlenderRNA *brna)
   RNA_def_property_ui_text(
       prop, "Distance", "Radius around curves roots in which no new curves can be added");
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+
+  prop = RNA_def_property(srna, "interpolate_length", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", CURVES_SCULPT_FLAG_INTERPOLATE_LENGTH);
+  RNA_def_property_ui_text(
+      prop, "Interpolate Length", "Use length of the curves in close proximity");
+
+  prop = RNA_def_property(srna, "interpolate_shape", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", CURVES_SCULPT_FLAG_INTERPOLATE_SHAPE);
+  RNA_def_property_ui_text(
+      prop, "Interpolate Shape", "Use shape of the curves in close proximity");
+
+  prop = RNA_def_property(srna, "curve_length", PROP_FLOAT, PROP_DISTANCE);
+  RNA_def_property_range(prop, 0.0, FLT_MAX);
+  RNA_def_property_ui_text(
+      prop,
+      "Curve Length",
+      "Length of newly added curves when it is not interpolated from other curves");
 }
 
 void RNA_def_sculpt_paint(BlenderRNA *brna)