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

1 files changed, 7 insertions, 1 deletions

diff --git a/source/blender/editors/sculpt_paint/paint_stroke.c b/source/blender/editors/sculpt_paint/paint_stroke.c
index c0bf89107e0..0f7b8ad1f3d 100644
--- a/source/blender/editors/sculpt_paint/paint_stroke.c
+++ b/source/blender/editors/sculpt_paint/paint_stroke.c
@@ -986,6 +986,11 @@ static void stroke_done(bContext *C, wmOperator *op, PaintStroke *stroke)
   paint_stroke_free(C, op, stroke);
 }
 
+static bool curves_sculpt_brush_uses_spacing(const eBrushCurvesSculptTool tool)
+{
+  return ELEM(tool, CURVES_SCULPT_TOOL_ADD);
+}
+
 bool paint_space_stroke_enabled(Brush *br, ePaintMode mode)
 {
   if ((br->flag & BRUSH_SPACE) == 0) {
@@ -1000,7 +1005,8 @@ bool paint_space_stroke_enabled(Brush *br, ePaintMode mode)
     return true;
   }
 
-  if (mode == PAINT_MODE_SCULPT_CURVES) {
+  if (mode == PAINT_MODE_SCULPT_CURVES &&
+      !curves_sculpt_brush_uses_spacing(br->curves_sculpt_tool)) {
     return false;
   }