Curves: new Grow/Shrink brush

This adds a new Grow/Shrink brush which is similar to the Length
brush in the old hair system.
* It's possible to switch between growing and shrinking by hold
  down ctrl and/or by changing the direction enum.
* 3d brush is supported.
* Different brush falloffs are supported.
* Supports scaling curves uniformly or shrinking/extrapolating
  them. Extrapolation is linear only in this patch.
* A minimum length settings helps to avoid creating zero-sized curves.

Differential Revision: https://developer.blender.org/D14474

release/scripts/presets/keyconfig/keymap_data/blender_default.py

@@ -5576,7 +5576,10 @@ def km_sculpt_curves(params):
     )
 
     items.extend([
-        ("sculpt_curves.brush_stroke", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("sculpt_curves.brush_stroke", {"type": 'LEFTMOUSE', "value": 'PRESS'},
+         {"properties": [("mode", 'NORMAL')]}),
+        ("sculpt_curves.brush_stroke", {"type": 'LEFTMOUSE', "value": 'PRESS', "ctrl": True},
+         {"properties": [("mode", 'INVERT')]}),
         *_template_paint_radial_control("curves_sculpt"),
     ])
 

release/scripts/startup/bl_ui/space_view3d.py

@@ -514,6 +514,13 @@ class _draw_tool_settings_context_mode:
             layout.prop(tool_settings.curves_sculpt, "interpolate_length")
             layout.prop(tool_settings.curves_sculpt, "interpolate_shape")
 
+        if brush.curves_sculpt_tool == 'GROW_SHRINK':
+            layout.prop(brush, "direction", expand=True, text="")
+            layout.prop(brush, "falloff_shape", expand=True)
+            layout.prop(brush.curves_sculpt_settings, "scale_uniform")
+            layout.prop(brush.curves_sculpt_settings, "minimum_length")
+            layout.prop(brush, "curve_preset")
+
         if brush.curves_sculpt_tool == 'SNAKE_HOOK':
             layout.prop(brush, "falloff_shape", expand=True)
             layout.prop(brush, "curve_preset")

source/blender/blenkernel/intern/brush.c

@@ -1558,6 +1558,7 @@ void BKE_brush_init_curves_sculpt_settings(Brush *brush)
     brush->curves_sculpt_settings = MEM_callocN(sizeof(BrushCurvesSculptSettings), __func__);
   }
   brush->curves_sculpt_settings->add_amount = 1;
+  brush->curves_sculpt_settings->minimum_length = 0.01f;
 }
 
 struct Brush *BKE_brush_first_search(struct Main *bmain, const eObjectMode ob_mode)

source/blender/blenlib/BLI_math_geom.h

@@ -329,6 +329,24 @@ float closest_to_line_segment_v2(float r_close[2],
                                  const float p[2],
                                  const float l1[2],
                                  const float l2[2]);
+
+/**
+ * Finds the points where two line segments are closest to each other.
+ *
+ * `lambda_*` is a value between 0 and 1 for each segment that indicates where `r_closest_*` is on
+ * the corresponding segment.
+ *
+ * \return Squared distance between both segments.
+ */
+float closest_seg_seg_v2(float r_closest_a[2],
+                         float r_closest_b[2],
+                         float *r_lambda_a,
+                         float *r_lambda_b,
+                         const float a1[2],
+                         const float a2[2],
+                         const float b1[2],
+                         const float b2[2]);
+
 /**
  * Point closest to v1 on line v2-v3 in 3D.
  *

source/blender/blenlib/intern/math_geom.c

@@ -294,6 +294,66 @@ float dist_to_line_segment_v2(const float p[2], const float l1[2], const float l
   return sqrtf(dist_squared_to_line_segment_v2(p, l1, l2));
 }
 
+float closest_seg_seg_v2(float r_closest_a[2],
+                         float r_closest_b[2],
+                         float *r_lambda_a,
+                         float *r_lambda_b,
+                         const float a1[2],
+                         const float a2[2],
+                         const float b1[2],
+                         const float b2[2])
+{
+  if (isect_seg_seg_v2_simple(a1, a2, b1, b2)) {
+    float intersection[2];
+    isect_line_line_v2_point(a1, a2, b1, b2, intersection);
+    copy_v2_v2(r_closest_a, intersection);
+    copy_v2_v2(r_closest_b, intersection);
+    float tmp[2];
+    *r_lambda_a = closest_to_line_v2(tmp, intersection, a1, a2);
+    *r_lambda_b = closest_to_line_v2(tmp, intersection, b1, b2);
+    const float min_dist_sq = len_squared_v2v2(r_closest_a, r_closest_b);
+    return min_dist_sq;
+  }
+
+  float p1[2], p2[2], p3[2], p4[2];
+  const float lambda1 = closest_to_line_segment_v2(p1, a1, b1, b2);
+  const float lambda2 = closest_to_line_segment_v2(p2, a2, b1, b2);
+  const float lambda3 = closest_to_line_segment_v2(p3, b1, a1, a2);
+  const float lambda4 = closest_to_line_segment_v2(p4, b2, a1, a2);
+  const float dist_sq1 = len_squared_v2v2(p1, a1);
+  const float dist_sq2 = len_squared_v2v2(p2, a2);
+  const float dist_sq3 = len_squared_v2v2(p3, b1);
+  const float dist_sq4 = len_squared_v2v2(p4, b2);
+
+  const float min_dist_sq = min_ffff(dist_sq1, dist_sq2, dist_sq3, dist_sq4);
+  if (min_dist_sq == dist_sq1) {
+    copy_v2_v2(r_closest_a, a1);
+    copy_v2_v2(r_closest_b, p1);
+    *r_lambda_a = 0.0f;
+    *r_lambda_b = lambda1;
+  }
+  else if (min_dist_sq == dist_sq2) {
+    copy_v2_v2(r_closest_a, a2);
+    copy_v2_v2(r_closest_b, p2);
+    *r_lambda_a = 1.0f;
+    *r_lambda_b = lambda2;
+  }
+  else if (min_dist_sq == dist_sq3) {
+    copy_v2_v2(r_closest_a, p3);
+    copy_v2_v2(r_closest_b, b1);
+    *r_lambda_a = lambda3;
+    *r_lambda_b = 0.0f;
+  }
+  else {
+    BLI_assert(min_dist_sq == dist_sq4);
+    copy_v2_v2(r_closest_a, p4);
+    copy_v2_v2(r_closest_b, b2);
+    *r_lambda_a = lambda4;
+    *r_lambda_b = 1.0f;
+  }
+  return min_dist_sq;
+}
+
 float closest_to_line_segment_v2(float r_close[2],
                                  const float p[2],
                                  const float l1[2],

source/blender/editors/datafiles/CMakeLists.txt

@@ -774,7 +774,7 @@ set_property(GLOBAL PROPERTY ICON_GEOM_NAMES
   ops.curves.sculpt_comb
   ops.curves.sculpt_cut
   ops.curves.sculpt_delete
-  ops.curves.sculpt_grow
+  ops.curves.sculpt_grow_shrink
   ops.generic.cursor
   ops.generic.select
   ops.generic.select_box

source/blender/editors/sculpt_paint/CMakeLists.txt

@@ -31,6 +31,7 @@ set(SRC
   curves_sculpt_add.cc
   curves_sculpt_comb.cc
   curves_sculpt_delete.cc
+  curves_sculpt_grow_shrink.cc
   curves_sculpt_ops.cc
   curves_sculpt_snake_hook.cc
   paint_cursor.c

source/blender/editors/sculpt_paint/curves_sculpt_grow_shrink.cc

@@ -0,0 +1,526 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <algorithm>
+
+#include "curves_sculpt_intern.hh"
+
+#include "BLI_enumerable_thread_specific.hh"
+#include "BLI_float4x4.hh"
+#include "BLI_kdtree.h"
+#include "BLI_rand.hh"
+#include "BLI_vector.hh"
+
+#include "PIL_time.h"
+
+#include "DEG_depsgraph.h"
+
+#include "BKE_attribute_math.hh"
+#include "BKE_brush.h"
+#include "BKE_bvhutils.h"
+#include "BKE_context.h"
+#include "BKE_curves.hh"
+#include "BKE_mesh.h"
+#include "BKE_mesh_runtime.h"
+#include "BKE_paint.h"
+#include "BKE_spline.hh"
+
+#include "DNA_brush_enums.h"
+#include "DNA_brush_types.h"
+#include "DNA_curves_types.h"
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+#include "DNA_object_types.h"
+#include "DNA_screen_types.h"
+#include "DNA_space_types.h"
+
+#include "ED_screen.h"
+#include "ED_view3d.h"
+
+#include "curves_sculpt_intern.hh"
+
+/**
+ * The code below uses a suffix naming convention to indicate the coordinate space:
+ * - `cu`: Local space of the curves object that is being edited.
+ * - `su`: Local space of the surface object.
+ * - `wo`: World space.
+ * - `re`: 2D coordinates within the region.
+ */
+
+namespace blender::ed::sculpt_paint {
+
+using bke::CurvesGeometry;
+
+/**
+ * Utility class to wrap different grow/shrink behaviors.
+ * It might be useful to use this for other future brushes as well, but better see if this
+ * abstraction holds up for a while before using it in more places.
+ */
+class CurvesEffect {
+ public:
+  virtual void execute(CurvesGeometry &curves,
+                       Span<int> curve_indices,
+                       Span<float> move_distances_cu) = 0;
+};
+
+/**
+ * Make curves smaller by trimming the end off.
+ */
+class ShrinkCurvesEffect : public CurvesEffect {
+ private:
+  Brush &brush_;
+
+ public:
+  ShrinkCurvesEffect(Brush &brush) : brush_(brush)
+  {
+  }
+
+  void execute(CurvesGeometry &curves,
+               const Span<int> curve_indices,
+               const Span<float> move_distances_cu) override
+  {
+    MutableSpan<float3> positions_cu = curves.positions();
+    threading::parallel_for(curve_indices.index_range(), 256, [&](const IndexRange range) {
+      for (const int influence_i : range) {
+        const int curve_i = curve_indices[influence_i];
+        const float move_distance_cu = move_distances_cu[influence_i];
+        const IndexRange curve_points = curves.points_for_curve(curve_i);
+        this->shrink_curve(positions_cu, curve_points, move_distance_cu);
+      }
+    });
+  }
+
+  void shrink_curve(MutableSpan<float3> positions,
+                    const IndexRange curve_points,
+                    const float shrink_length) const
+  {
+    PolySpline spline;
+    spline.resize(curve_points.size());
+    MutableSpan<float3> spline_positions = spline.positions();
+    spline_positions.copy_from(positions.slice(curve_points));
+    spline.mark_cache_invalid();
+    const float min_length = brush_.curves_sculpt_settings->minimum_length;
+    const float old_length = spline.length();
+    const float new_length = std::max(min_length, old_length - shrink_length);
+    const float length_factor = std::clamp(new_length / old_length, 0.0f, 1.0f);
+
+    Vector<float> old_point_lengths;
+    old_point_lengths.append(0.0f);
+    for (const int i : spline_positions.index_range().drop_back(1)) {
+      const float3 &p1 = spline_positions[i];
+      const float3 &p2 = spline_positions[i + 1];
+      const float length = math::distance(p1, p2);
+      old_point_lengths.append(old_point_lengths.last() + length);
+    }
+
+    for (const int i : spline_positions.index_range()) {
+      const float eval_length = old_point_lengths[i] * length_factor;
+      const Spline::LookupResult lookup = spline.lookup_evaluated_length(eval_length);
+      const float index_factor = lookup.evaluated_index + lookup.factor;
+      float3 p;
+      spline.sample_with_index_factors<float3>(spline_positions, {&index_factor, 1}, {&p, 1});
+      positions[curve_points[i]] = p;
+    }
+  }
+};
+
+/**
+ * Make the curves longer by extrapolating them linearly.
+ */
+class ExtrapolateCurvesEffect : public CurvesEffect {
+  void execute(CurvesGeometry &curves,
+               const Span<int> curve_indices,
+               const Span<float> move_distances_cu) override
+  {
+    MutableSpan<float3> positions_cu = curves.positions();
+    threading::parallel_for(curve_indices.index_range(), 256, [&](const IndexRange range) {
+      for (const int influence_i : range) {
+        const int curve_i = curve_indices[influence_i];
+        const float move_distance_cu = move_distances_cu[influence_i];
+        const IndexRange curve_points = curves.points_for_curve(curve_i);
+
+        if (curve_points.size() <= 1) {
+          continue;
+        }
+
+        const float3 old_last_pos_cu = positions_cu[curve_points.last()];
+        /* Use some point within the curve rather than the end point to smooth out some random
+         * variation. */
+        const float3 direction_reference_point =
+            positions_cu[curve_points[curve_points.size() / 2]];
+        const float3 direction = math::normalize(old_last_pos_cu - direction_reference_point);
+
+        const float3 new_last_pos_cu = old_last_pos_cu + direction * move_distance_cu;
+        this->move_last_point_and_resample(positions_cu, curve_points, new_last_pos_cu);
+      }
+    });
+  }
+
+  void move_last_point_and_resample(MutableSpan<float3> positions,
+                                    const IndexRange curve_points,
+                                    const float3 &new_last_point_position) const
+  {
+    Vector<float> old_lengths;
+    old_lengths.append(0.0f);
+    /* Used to (1) normalize the segment sizes over time and (2) support making zero-length
+     * segments */
+    const float extra_length = 0.001f;
+    for (const int segment_i : IndexRange(curve_points.size() - 1)) {
+      const float3 &p1 = positions[curve_points[segment_i]];
+      const float3 &p2 = positions[curve_points[segment_i] + 1];
+      const float length = math::distance(p1, p2);
+      old_lengths.append(old_lengths.last() + length + extra_length);
+    }
+    Vector<float> point_factors;
+    for (float &old_length : old_lengths) {
+      point_factors.append(old_length / old_lengths.last());
+    }
+
+    PolySpline new_spline;
+    new_spline.resize(curve_points.size());
+    MutableSpan<float3> new_spline_positions = new_spline.positions();
+    for (const int i : IndexRange(curve_points.size() - 1)) {
+      new_spline_positions[i] = positions[curve_points[i]];
+    }
+    new_spline_positions.last() = new_last_point_position;
+    new_spline.mark_cache_invalid();
+
+    for (const int i : IndexRange(curve_points.size())) {
+      const float factor = point_factors[i];
+      const Spline::LookupResult lookup = new_spline.lookup_evaluated_factor(factor);
+      const float index_factor = lookup.evaluated_index + lookup.factor;
+      float3 p;
+      new_spline.sample_with_index_factors<float3>(
+          new_spline_positions, {&index_factor, 1}, {&p, 1});
+      positions[curve_points[i]] = p;
+    }
+  }
+};
+
+/**
+ * Change the length of curves by scaling them uniformly.
+ */
+class ScaleCurvesEffect : public CurvesEffect {
+ private:
+  bool scale_up_;
+  Brush &brush_;
+
+ public:
+  ScaleCurvesEffect(bool scale_up, Brush &brush) : scale_up_(scale_up), brush_(brush)
+  {
+  }
+
+  void execute(CurvesGeometry &curves,
+               const Span<int> curve_indices,
+               const Span<float> move_distances_cu) override
+  {
+    MutableSpan<float3> positions_cu = curves.positions();
+    threading::parallel_for(curve_indices.index_range(), 256, [&](const IndexRange range) {
+      for (const int influence_i : range) {
+        const int curve_i = curve_indices[influence_i];
+        const float move_distance_cu = move_distances_cu[influence_i];
+        const IndexRange points = curves.points_for_curve(curve_i);
+
+        const float old_length = this->compute_poly_curve_length(positions_cu.slice(points));
+        const float length_diff = scale_up_ ? move_distance_cu : -move_distance_cu;
+        const float min_length = brush_.curves_sculpt_settings->minimum_length;
+        const float new_length = std::max(min_length, old_length + length_diff);
+        const float scale_factor = safe_divide(new_length, old_length);
+
+        const float3 &root_pos_cu = positions_cu[points[0]];
+        for (float3 &pos_cu : positions_cu.slice(points.drop_front(1))) {
+          pos_cu = (pos_cu - root_pos_cu) * scale_factor + root_pos_cu;
+        }
+      }
+    });
+  }
+
+  float compute_poly_curve_length(const Span<float3> positions)
+  {
+    float length = 0.0f;
+    const int segments_num = positions.size() - 1;
+    for (const int segment_i : IndexRange(segments_num)) {
+      const float3 &p1 = positions[segment_i];
+      const float3 &p2 = positions[segment_i + 1];
+      length += math::distance(p1, p2);
+    }
+    return length;
+  }
+};
+
+class CurvesEffectOperation : public CurvesSculptStrokeOperation {
+ private:
+  std::unique_ptr<CurvesEffect> effect_;
+  float2 last_mouse_position_;
+  CurvesBrush3D brush_3d_;
+
+  friend struct CurvesEffectOperationExecutor;
+
+ public:
+  CurvesEffectOperation(std::unique_ptr<CurvesEffect> effect) : effect_(std::move(effect))
+  {
+  }
+
+  void on_stroke_extended(bContext *C, const StrokeExtension &stroke_extension) override;
+};
+
+/**
+ * Utility class that actually executes the update when the stroke is updated. That's useful
+ * because it avoids passing a very large number of parameters between functions.
+ */
+struct CurvesEffectOperationExecutor {
+  CurvesEffectOperation *self_ = nullptr;
+  Depsgraph *depsgraph_ = nullptr;
+  Scene *scene_ = nullptr;
+  Object *object_ = nullptr;
+  ARegion *region_ = nullptr;
+  View3D *v3d_ = nullptr;
+  RegionView3D *rv3d_ = nullptr;
+
+  Curves *curves_id_ = nullptr;
+  CurvesGeometry *curves_ = nullptr;
+
+  Brush *brush_ = nullptr;
+  float brush_radius_re_;
+  float brush_radius_sq_re_;
+  float brush_strength_;
+  eBrushFalloffShape falloff_shape_;
+
+  float4x4 curves_to_world_mat_;
+  float4x4 world_to_curves_mat_;
+
+  float2 brush_pos_start_re_;
+  float2 brush_pos_end_re_;
+
+  struct Influences {
+    Vector<int> curve_indices;
+    Vector<float> move_distances_cu;
+  };
+
+  void execute(CurvesEffectOperation &self, bContext *C, const StrokeExtension &stroke_extension)
+  {
+    BLI_SCOPED_DEFER([&]() { self.last_mouse_position_ = stroke_extension.mouse_position; });
+
+    self_ = &self;
+    depsgraph_ = CTX_data_depsgraph_pointer(C);
+    scene_ = CTX_data_scene(C);
+    object_ = CTX_data_active_object(C);
+    region_ = CTX_wm_region(C);
+    v3d_ = CTX_wm_view3d(C);
+    rv3d_ = CTX_wm_region_view3d(C);
+
+    curves_id_ = static_cast<Curves *>(object_->data);
+    curves_ = &CurvesGeometry::wrap(curves_id_->geometry);
+
+    CurvesSculpt &curves_sculpt = *scene_->toolsettings->curves_sculpt;
+    brush_ = BKE_paint_brush(&curves_sculpt.paint);
+    brush_radius_re_ = BKE_brush_size_get(scene_, brush_);
+    brush_strength_ = BKE_brush_alpha_get(scene_, brush_);
+    brush_radius_sq_re_ = pow2f(brush_radius_re_);
+    falloff_shape_ = eBrushFalloffShape(brush_->falloff_shape);
+
+    curves_to_world_mat_ = object_->obmat;
+    world_to_curves_mat_ = curves_to_world_mat_.inverted();
+
+    brush_pos_start_re_ = self.last_mouse_position_;
+    brush_pos_end_re_ = stroke_extension.mouse_position;
+
+    if (stroke_extension.is_first) {
+      if (falloff_shape_ == PAINT_FALLOFF_SHAPE_SPHERE) {
+        if (std::optional<CurvesBrush3D> brush_3d = sample_curves_3d_brush(
+                *C, *object_, stroke_extension.mouse_position, brush_radius_re_)) {
+          self.brush_3d_ = *brush_3d;
+        }
+      }
+
+      return;
+    }
+
+    /* Compute influences. */
+    threading::EnumerableThreadSpecific<Influences> influences_for_thread;
+    if (falloff_shape_ == PAINT_FALLOFF_SHAPE_TUBE) {
+      this->gather_influences_projected(influences_for_thread);
+    }
+    else if (falloff_shape_ == PAINT_FALLOFF_SHAPE_SPHERE) {
+      this->gather_influences_spherical(influences_for_thread);
+    }
+
+    /* Execute effect. */
+    threading::parallel_for_each(influences_for_thread, [&](const Influences &influences) {
+      BLI_assert(influences.curve_indices.size() == influences.move_distances_cu.size());
+      self_->effect_->execute(*curves_, influences.curve_indices, influences.move_distances_cu);
+    });
+
+    curves_->tag_positions_changed();
+    DEG_id_tag_update(&curves_id_->id, ID_RECALC_GEOMETRY);
+    ED_region_tag_redraw(region_);
+  }
+
+  void gather_influences_projected(
+      threading::EnumerableThreadSpecific<Influences> &influences_for_thread)
+  {
+    const Span<float3> positions_cu = curves_->positions();
+
+    float4x4 projection;
+    ED_view3d_ob_project_mat_get(rv3d_, object_, projection.values);
+
+    threading::parallel_for(curves_->curves_range(), 256, [&](const IndexRange curves_range) {
+      Influences &local_influences = influences_for_thread.local();
+
+      for (const int curve_i : curves_range) {
+        const IndexRange points = curves_->points_for_curve(curve_i);
+        const int tot_segments = points.size() - 1;
+        float max_move_distance_cu = 0.0f;
+        for (const int segment_i : IndexRange(tot_segments)) {
+          const float3 &p1_cu = positions_cu[points[segment_i]];
+          const float3 &p2_cu = positions_cu[points[segment_i] + 1];
+
+          float2 p1_re, p2_re;
+          ED_view3d_project_float_v2_m4(region_, p1_cu, p1_re, projection.values);
+          ED_view3d_project_float_v2_m4(region_, p2_cu, p2_re, projection.values);
+
+          float2 closest_on_brush_re;
+          float2 closest_on_segment_re;
+          float lambda_on_brush;
+          float lambda_on_segment;
+          const float dist_to_brush_sq_re = closest_seg_seg_v2(closest_on_brush_re,
+                                                               closest_on_segment_re,
+                                                               &lambda_on_brush,
+                                                               &lambda_on_segment,
+                                                               brush_pos_start_re_,
+                                                               brush_pos_end_re_,
+                                                               p1_re,
+                                                               p2_re);
+
+          if (dist_to_brush_sq_re > brush_radius_sq_re_) {
+            continue;
+          }
+
+          const float dist_to_brush_re = std::sqrt(dist_to_brush_sq_re);
+          const float radius_falloff = BKE_brush_curve_strength(
+              brush_, dist_to_brush_re, brush_radius_re_);
+          const float weight = brush_strength_ * radius_falloff;
+
+          const float3 closest_on_segment_cu = math::interpolate(p1_cu, p2_cu, lambda_on_segment);
+
+          float3 brush_start_pos_wo, brush_end_pos_wo;
+          ED_view3d_win_to_3d(v3d_,
+                              region_,
+                              curves_to_world_mat_ * closest_on_segment_cu,
+                              brush_pos_start_re_,
+                              brush_start_pos_wo);
+          ED_view3d_win_to_3d(v3d_,
+                              region_,
+                              curves_to_world_mat_ * closest_on_segment_cu,
+                              brush_pos_end_re_,
+                              brush_end_pos_wo);
+          const float3 brush_start_pos_cu = world_to_curves_mat_ * brush_start_pos_wo;
+          const float3 brush_end_pos_cu = world_to_curves_mat_ * brush_end_pos_wo;
+
+          const float move_distance_cu = weight *
+                                         math::distance(brush_start_pos_cu, brush_end_pos_cu);
+          max_move_distance_cu = std::max(max_move_distance_cu, move_distance_cu);
+        }
+        if (max_move_distance_cu > 0.0f) {
+          local_influences.curve_indices.append(curve_i);
+          local_influences.move_distances_cu.append(max_move_distance_cu);
+        }
+      }
+    });
+  }
+
+  void gather_influences_spherical(
+      threading::EnumerableThreadSpecific<Influences> &influences_for_thread)
+  {
+    const Span<float3> positions_cu = curves_->positions();
+
+    float3 brush_pos_start_wo, brush_pos_end_wo;
+    ED_view3d_win_to_3d(v3d_,
+                        region_,
+                        curves_to_world_mat_ * self_->brush_3d_.position_cu,
+                        brush_pos_start_re_,
+                        brush_pos_start_wo);
+    ED_view3d_win_to_3d(v3d_,
+                        region_,
+                        curves_to_world_mat_ * self_->brush_3d_.position_cu,
+                        brush_pos_end_re_,
+                        brush_pos_end_wo);
+    const float3 brush_pos_start_cu = world_to_curves_mat_ * brush_pos_start_wo;
+    const float3 brush_pos_end_cu = world_to_curves_mat_ * brush_pos_end_wo;
+    const float3 brush_pos_diff_cu = brush_pos_end_cu - brush_pos_start_cu;
+    const float brush_pos_diff_length_cu = math::length(brush_pos_diff_cu);
+    const float brush_radius_cu = self_->brush_3d_.radius_cu;
+    const float brush_radius_sq_cu = pow2f(brush_radius_cu);
+    threading::parallel_for(curves_->curves_range(), 256, [&](const IndexRange curves_range) {
+      Influences &local_influences = influences_for_thread.local();
+
+      for (const int curve_i : curves_range) {
+        const IndexRange points = curves_->points_for_curve(curve_i);
+        const int tot_segments = points.size() - 1;
+        float max_move_distance_cu = 0.0f;
+        for (const int segment_i : IndexRange(tot_segments)) {
+          const float3 &p1_cu = positions_cu[points[segment_i]];
+          const float3 &p2_cu = positions_cu[points[segment_i] + 1];
+
+          float3 closest_on_segment_cu;
+          float3 closest_on_brush_cu;
+          isect_seg_seg_v3(p1_cu,
+                           p2_cu,
+                           brush_pos_start_cu,
+                           brush_pos_end_cu,
+                           closest_on_segment_cu,
+                           closest_on_brush_cu);
+
+          const float dist_to_brush_sq_cu = math::distance_squared(closest_on_segment_cu,
+                                                                   closest_on_brush_cu);
+          if (dist_to_brush_sq_cu > brush_radius_sq_cu) {
+            continue;
+          }
+
+          const float dist_to_brush_cu = std::sqrt(dist_to_brush_sq_cu);
+          const float radius_falloff = BKE_brush_curve_strength(
+              brush_, dist_to_brush_cu, brush_radius_cu);
+          const float weight = brush_strength_ * radius_falloff;
+
+          const float move_distance_cu = weight * brush_pos_diff_length_cu;
+          max_move_distance_cu = std::max(max_move_distance_cu, move_distance_cu);
+        }
+        if (max_move_distance_cu > 0.0f) {
+          local_influences.curve_indices.append(curve_i);
+          local_influences.move_distances_cu.append(max_move_distance_cu);
+        }
+      }
+    });
+  }
+};
+
+void CurvesEffectOperation::on_stroke_extended(bContext *C,
+                                               const StrokeExtension &stroke_extension)
+{
+  CurvesEffectOperationExecutor executor;
+  executor.execute(*this, C, stroke_extension);
+}
+
+std::unique_ptr<CurvesSculptStrokeOperation> new_grow_shrink_operation(
+    const BrushStrokeMode brush_mode, bContext *C)
+{
+  Scene &scene = *CTX_data_scene(C);
+  Brush &brush = *BKE_paint_brush(&scene.toolsettings->curves_sculpt->paint);
+  const bool use_scale_uniform = brush.curves_sculpt_settings->flag &
+                                 BRUSH_CURVES_SCULPT_FLAG_SCALE_UNIFORM;
+  const bool use_grow = (brush_mode == BRUSH_STROKE_INVERT) == ((brush.flag & BRUSH_DIR_IN) != 0);
+
+  if (use_grow) {
+    if (use_scale_uniform) {
+      return std::make_unique<CurvesEffectOperation>(
+          std::make_unique<ScaleCurvesEffect>(true, brush));
+    }
+    return std::make_unique<CurvesEffectOperation>(std::make_unique<ExtrapolateCurvesEffect>());
+  }
+  if (use_scale_uniform) {
+    return std::make_unique<CurvesEffectOperation>(
+        std::make_unique<ScaleCurvesEffect>(false, brush));
+  }
+  return std::make_unique<CurvesEffectOperation>(std::make_unique<ShrinkCurvesEffect>(brush));
+}
+
+}  // namespace blender::ed::sculpt_paint

source/blender/editors/sculpt_paint/curves_sculpt_intern.hh

@@ -5,6 +5,7 @@
 #include <optional>
 
 #include "curves_sculpt_intern.h"
+#include "paint_intern.h"
 
 #include "BLI_math_vector.hh"
 
@@ -36,6 +37,8 @@ std::unique_ptr<CurvesSculptStrokeOperation> new_add_operation();
 std::unique_ptr<CurvesSculptStrokeOperation> new_comb_operation();
 std::unique_ptr<CurvesSculptStrokeOperation> new_delete_operation();
 std::unique_ptr<CurvesSculptStrokeOperation> new_snake_hook_operation();
+std::unique_ptr<CurvesSculptStrokeOperation> new_grow_shrink_operation(
+    const BrushStrokeMode brush_mode, bContext *C);
 
 struct CurvesBrush3D {
   float3 position_cu;

source/blender/editors/sculpt_paint/curves_sculpt_ops.cc

@@ -74,118 +74,6 @@ using blender::bke::CurvesGeometry;
 /** \name * SCULPT_CURVES_OT_brush_stroke
  * \{ */
 
-/**
- * Resamples the curves to a shorter length.
- */
-class ShrinkOperation : public CurvesSculptStrokeOperation {
- private:
-  float2 last_mouse_position_;
-
- public:
-  void on_stroke_extended(bContext *C, const StrokeExtension &stroke_extension) override
-  {
-    BLI_SCOPED_DEFER([&]() { last_mouse_position_ = stroke_extension.mouse_position; });
-
-    if (stroke_extension.is_first) {
-      return;
-    }
-
-    Scene &scene = *CTX_data_scene(C);
-    Object &object = *CTX_data_active_object(C);
-    ARegion *region = CTX_wm_region(C);
-    View3D *v3d = CTX_wm_view3d(C);
-    RegionView3D *rv3d = CTX_wm_region_view3d(C);
-
-    CurvesSculpt &curves_sculpt = *scene.toolsettings->curves_sculpt;
-    Brush &brush = *BKE_paint_brush(&curves_sculpt.paint);
-    const float brush_radius = BKE_brush_size_get(&scene, &brush);
-    const float brush_strength = BKE_brush_alpha_get(&scene, &brush);
-
-    const float4x4 ob_mat = object.obmat;
-    const float4x4 ob_imat = ob_mat.inverted();
-
-    float4x4 projection;
-    ED_view3d_ob_project_mat_get(rv3d, &object, projection.values);
-
-    Curves &curves_id = *static_cast<Curves *>(object.data);
-    CurvesGeometry &curves = CurvesGeometry::wrap(curves_id.geometry);
-    MutableSpan<float3> positions = curves.positions();
-
-    const float2 mouse_prev = last_mouse_position_;
-    const float2 mouse_cur = stroke_extension.mouse_position;
-    const float2 mouse_diff = mouse_cur - mouse_prev;
-
-    threading::parallel_for(curves.curves_range(), 256, [&](const IndexRange curves_range) {
-      for (const int curve_i : curves_range) {
-        const IndexRange curve_points = curves.points_for_curve(curve_i);
-        const int last_point_i = curve_points.last();
-
-        const float3 old_tip_position = positions[last_point_i];
-
-        float2 old_tip_position_screen;
-        ED_view3d_project_float_v2_m4(
-            region, old_tip_position, old_tip_position_screen, projection.values);
-
-        const float distance_screen = math::distance(old_tip_position_screen, mouse_prev);
-        if (distance_screen > brush_radius) {
-          continue;
-        }
-
-        const float radius_falloff = pow2f(1.0f - distance_screen / brush_radius);
-        const float weight = brush_strength * radius_falloff;
-
-        const float2 offset_tip_position_screen = old_tip_position_screen + weight * mouse_diff;
-        float3 offset_tip_position;
-        ED_view3d_win_to_3d(v3d,
-                            region,
-                            ob_mat * old_tip_position,
-                            offset_tip_position_screen,
-                            offset_tip_position);
-        offset_tip_position = ob_imat * offset_tip_position;
-        const float shrink_length = math::distance(offset_tip_position, old_tip_position);
-
-        this->shrink_curve(positions, curve_points, shrink_length);
-      }
-    });
-
-    curves.tag_positions_changed();
-    DEG_id_tag_update(&curves_id.id, ID_RECALC_GEOMETRY);
-    ED_region_tag_redraw(region);
-  }
-
-  void shrink_curve(MutableSpan<float3> positions,
-                    const IndexRange curve_points,
-                    const float shrink_length) const
-  {
-    PolySpline spline;
-    spline.resize(curve_points.size());
-    MutableSpan<float3> spline_positions = spline.positions();
-    spline_positions.copy_from(positions.slice(curve_points));
-    spline.mark_cache_invalid();
-    const float old_length = spline.length();
-    const float new_length = std::max(0.0f, old_length - shrink_length);
-    const float length_factor = new_length / old_length;
-
-    Vector<float> old_point_lengths;
-    old_point_lengths.append(0.0f);
-    for (const int i : spline_positions.index_range().drop_back(1)) {
-      const float3 &p1 = spline_positions[i];
-      const float3 &p2 = spline_positions[i + 1];
-      const float length = math::distance(p1, p2);
-      old_point_lengths.append(old_point_lengths.last() + length);
-    }
-
-    for (const int i : spline_positions.index_range()) {
-      const float eval_length = old_point_lengths[i] * length_factor;
-      const Spline::LookupResult lookup = spline.lookup_evaluated_length(eval_length);
-      const float index_factor = lookup.evaluated_index + lookup.factor;
-      float3 p;
-      spline.sample_with_index_factors<float3>(spline_positions, {&index_factor, 1}, {&p, 1});
-      positions[curve_points[i]] = p;
-    }
-  }
-};
-
 class DensityAddOperation : public CurvesSculptStrokeOperation {
  private:
   /** Contains the root points of the curves that existed before this operation started. */
@@ -612,8 +500,10 @@ class DensityAddOperation : public CurvesSculptStrokeOperation {
 };
 
 static std::unique_ptr<CurvesSculptStrokeOperation> start_brush_operation(bContext *C,
-                                                                          wmOperator *UNUSED(op))
+                                                                          wmOperator *op)
 {
+  const BrushStrokeMode mode = static_cast<BrushStrokeMode>(RNA_enum_get(op->ptr, "mode"));
+
   Scene &scene = *CTX_data_scene(C);
   CurvesSculpt &curves_sculpt = *scene.toolsettings->curves_sculpt;
   Brush &brush = *BKE_paint_brush(&curves_sculpt.paint);
@@ -626,10 +516,10 @@ static std::unique_ptr<CurvesSculptStrokeOperation> start_brush_operation(bConte
       return new_snake_hook_operation();
     case CURVES_SCULPT_TOOL_ADD:
       return new_add_operation();
+    case CURVES_SCULPT_TOOL_GROW_SHRINK:
+      return new_grow_shrink_operation(mode, C);
     case CURVES_SCULPT_TOOL_TEST1:
       return std::make_unique<DensityAddOperation>();
-    case CURVES_SCULPT_TOOL_TEST2:
-      return std::make_unique<ShrinkOperation>();
   }
   BLI_assert_unreachable();
   return {};
@@ -674,7 +564,9 @@ static void stroke_update_step(bContext *C,
     stroke_extension.is_first = false;
   }
 
-  op_data->operation->on_stroke_extended(C, stroke_extension);
+  if (op_data->operation) {
+    op_data->operation->on_stroke_extended(C, stroke_extension);
+  }
 }
 
 static void stroke_done(const bContext *C, PaintStroke *stroke)

source/blender/makesdna/DNA_brush_enums.h

@@ -461,8 +461,8 @@ typedef enum eBrushCurvesSculptTool {
   CURVES_SCULPT_TOOL_DELETE = 1,
   CURVES_SCULPT_TOOL_SNAKE_HOOK = 2,
   CURVES_SCULPT_TOOL_ADD = 3,
-  CURVES_SCULPT_TOOL_TEST1 = 4,
-  CURVES_SCULPT_TOOL_TEST2 = 5,
+  CURVES_SCULPT_TOOL_GROW_SHRINK = 4,
+  CURVES_SCULPT_TOOL_TEST1 = 5,
 } eBrushCurvesSculptTool;
 
 /** When #BRUSH_ACCUMULATE is used */
@@ -608,6 +608,11 @@ typedef enum eBrushFalloffShape {
   PAINT_FALLOFF_SHAPE_TUBE = 1,
 } eBrushFalloffShape;
 
+typedef enum eBrushCurvesSculptFlag {
+  BRUSH_CURVES_SCULPT_FLAG_SCALE_UNIFORM = (1 << 0),
+  BRUSH_CURVES_SCULPT_FLAG_GROW_SHRINK_INVERT = (1 << 1),
+} eBrushCurvesSculptFlag;
+
 #define MAX_BRUSH_PIXEL_RADIUS 500
 #define GP_MAX_BRUSH_PIXEL_RADIUS 1000
 

source/blender/makesdna/DNA_brush_types.h

@@ -140,6 +140,10 @@ typedef struct BrushGpencilSettings {
 typedef struct BrushCurvesSculptSettings {
   /** Number of curves added by the add brush. */
   int add_amount;
+  /* eBrushCurvesSculptFlag. */
+  uint32_t flag;
+  /** When shrinking curves, they shouldn't become shorter than this length. */
+  float minimum_length;
 } BrushCurvesSculptSettings;
 
 typedef struct Brush {

source/blender/makesrna/intern/rna_brush.c

@@ -248,8 +248,8 @@ const EnumPropertyItem rna_enum_brush_curves_sculpt_tool_items[] = {
     {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_GROW_SHRINK, "GROW_SHRINK", ICON_NONE, "Grow / Shrink", ""},
     {CURVES_SCULPT_TOOL_TEST1, "TEST1", ICON_NONE, "Test 1", ""},
-    {CURVES_SCULPT_TOOL_TEST2, "TEST2", ICON_NONE, "Test 2", ""},
     {0, NULL, 0, NULL, NULL},
 };
 
@@ -883,7 +883,13 @@ static const EnumPropertyItem *rna_Brush_direction_itemf(bContext *C,
         default:
           return DummyRNA_DEFAULT_items;
       }
-
+    case PAINT_MODE_SCULPT_CURVES:
+      switch (me->curves_sculpt_tool) {
+        case CURVES_SCULPT_TOOL_GROW_SHRINK:
+          return prop_direction_items;
+        default:
+          return DummyRNA_DEFAULT_items;
+      }
     default:
       return DummyRNA_DEFAULT_items;
   }
@@ -1927,6 +1933,18 @@ static void rna_def_curves_sculpt_options(BlenderRNA *brna)
   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");
+
+  prop = RNA_def_property(srna, "scale_uniform", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", BRUSH_CURVES_SCULPT_FLAG_SCALE_UNIFORM);
+  RNA_def_property_ui_text(prop,
+                           "Scale Uniform",
+                           "Grow or shrink curves by changing their size uniformly instead of "
+                           "using trimming or extrapolation");
+
+  prop = RNA_def_property(srna, "minimum_length", PROP_FLOAT, PROP_DISTANCE);
+  RNA_def_property_range(prop, 0.0f, FLT_MAX);
+  RNA_def_property_ui_text(
+      prop, "Minimum Length", "Avoid shrinking curves shorter than this length");
 }
 
 static void rna_def_brush(BlenderRNA *brna)