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, 23 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/brush.c b/source/blender/blenkernel/intern/brush.c
index 6ee6ff7f41d..ff07d061a20 100644
--- a/source/blender/blenkernel/intern/brush.c
+++ b/source/blender/blenkernel/intern/brush.c
@@ -94,6 +94,9 @@ static void brush_copy_data(Main *UNUSED(bmain), ID *id_dst, const ID *id_src, c
     brush_dst->gpencil_settings->curve_rand_value = BKE_curvemapping_copy(
         brush_src->gpencil_settings->curve_rand_value);
   }
+  if (brush_src->curves_sculpt_settings != NULL) {
+    brush_dst->curves_sculpt_settings = MEM_dupallocN(brush_src->curves_sculpt_settings);
+  }
 
   /* enable fake user by default */
   id_fake_user_set(&brush_dst->id);
@@ -121,6 +124,9 @@ static void brush_free_data(ID *id)
 
     MEM_SAFE_FREE(brush->gpencil_settings);
   }
+  if (brush->curves_sculpt_settings != NULL) {
+    MEM_freeN(brush->curves_sculpt_settings);
+  }
 
   MEM_SAFE_FREE(brush->gradient);
 
@@ -236,6 +242,9 @@ static void brush_blend_write(BlendWriter *writer, ID *id, const void *id_addres
       BKE_curvemapping_blend_write(writer, brush->gpencil_settings->curve_rand_value);
     }
   }
+  if (brush->curves_sculpt_settings) {
+    BLO_write_struct(writer, BrushCurvesSculptSettings, brush->curves_sculpt_settings);
+  }
   if (brush->gradient) {
     BLO_write_struct(writer, ColorBand, brush->gradient);
   }
@@ -308,6 +317,8 @@ static void brush_blend_read_data(BlendDataReader *reader, ID *id)
     }
   }
 
+  BLO_read_data_address(reader, &brush->curves_sculpt_settings);
+
   brush->preview = NULL;
   brush->icon_imbuf = NULL;
 }
@@ -489,6 +500,10 @@ Brush *BKE_brush_add(Main *bmain, const char *name, const eObjectMode ob_mode)
 
   brush->ob_mode = ob_mode;
 
+  if (ob_mode == OB_MODE_SCULPT_CURVES) {
+    BKE_brush_init_curves_sculpt_settings(brush);
+  }
+
   return brush;
 }
 
@@ -1537,6 +1552,14 @@ void BKE_brush_gpencil_weight_presets(Main *bmain, ToolSettings *ts, const bool
   }
 }
 
+void BKE_brush_init_curves_sculpt_settings(Brush *brush)
+{
+  if (brush->curves_sculpt_settings == NULL) {
+    brush->curves_sculpt_settings = MEM_callocN(sizeof(BrushCurvesSculptSettings), __func__);
+  }
+  brush->curves_sculpt_settings->add_amount = 1;
+}
+
 struct Brush *BKE_brush_first_search(struct Main *bmain, const eObjectMode ob_mode)
 {
   Brush *brush;