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, 13 insertions, 1 deletions

diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index ebc5ebe758f..be8f9f938a3 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -993,11 +993,23 @@ typedef struct Sculpt {
   struct Object *gravity_object;
 } Sculpt;
 
+typedef enum CurvesSculptFlag {
+  CURVES_SCULPT_FLAG_INTERPOLATE_LENGTH = (1 << 0),
+  CURVES_SCULPT_FLAG_INTERPOLATE_SHAPE = (1 << 1),
+} CurvesSculptFlag;
+
 typedef struct CurvesSculpt {
   Paint paint;
   /** Minimum distance between newly added curves on a surface. */
   float distance;
-  char _pad1[4];
+
+  /** CurvesSculptFlag. */
+  uint32_t flag;
+
+  /** Length of newly added curves when it is not interpolated from other curves. */
+  float curve_length;
+
+  char _pad[4];
 } CurvesSculpt;
 
 typedef struct UvSculpt {