grease_pencil_utils.cc

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */

 
#include "BKE_attribute.hh"
#include "BKE_brush.hh"
#include "BKE_colortools.hh"
#include "BKE_context.hh"
#include "BKE_grease_pencil.hh"
#include "BKE_material.h"
#include "BKE_paint.hh"
#include "BKE_report.hh"
#include "BKE_scene.hh"
 
#include "BLI_math_geom.h"
#include "BLI_math_numbers.hh"
#include "BLI_math_vector.hh"
#include "BLI_vector_set.hh"
 
#include "DNA_brush_types.h"
#include "DNA_material_types.h"
#include "DNA_object_types.h"
#include "DNA_scene_types.h"
#include "DNA_view3d_types.h"
 
#include "RNA_prototypes.hh"
 
#include "ED_curves.hh"
#include "ED_grease_pencil.hh"
#include "ED_view3d.hh"
 
namespace blender::ed::greasepencil {
 
DrawingPlacement::DrawingPlacement(const Scene &scene,
                                   const ARegion &region,
                                   const View3D &view3d,
                                   const Object &eval_object,
                                   const bke::greasepencil::Layer *layer)
    : region_(&region), view3d_(&view3d)
{
  layer_space_to_world_space_ = (layer != nullptr) ? layer->to_world_space(eval_object) :
                                                     eval_object.object_to_world();
  world_space_to_layer_space_ = math::invert(layer_space_to_world_space_);
  /* Initialize DrawingPlacementPlane from toolsettings. */
  switch (scene.toolsettings->gp_sculpt.lock_axis) {
    case GP_LOCKAXIS_VIEW:
      plane_ = DrawingPlacementPlane::View;
      break;
    case GP_LOCKAXIS_Y:
      plane_ = DrawingPlacementPlane::Front;
      placement_normal_ = float3(0, 1, 0);
      break;
    case GP_LOCKAXIS_X:
      plane_ = DrawingPlacementPlane::Side;
      placement_normal_ = float3(1, 0, 0);
      break;
    case GP_LOCKAXIS_Z:
      plane_ = DrawingPlacementPlane::Top;
      placement_normal_ = float3(0, 0, 1);
      break;
    case GP_LOCKAXIS_CURSOR: {
      plane_ = DrawingPlacementPlane::Cursor;
      placement_normal_ = scene.cursor.matrix<float3x3>() * float3(0, 0, 1);
      break;
    }
  }
 
  /* Account for layer transform. */
  if (!ELEM(scene.toolsettings->gp_sculpt.lock_axis, GP_LOCKAXIS_VIEW, GP_LOCKAXIS_CURSOR)) {
    /* Use the transpose inverse for normal. */
    placement_normal_ = math::transform_direction(math::transpose(world_space_to_layer_space_),
                                                  placement_normal_);
  }
 
  /* Initialize DrawingPlacementDepth from toolsettings. */
  const char align_flag = scene.toolsettings->gpencil_v3d_align;
  if (align_flag & GP_PROJECT_VIEWSPACE) {
    if (align_flag & GP_PROJECT_CURSOR) {
      depth_ = DrawingPlacementDepth::Cursor;
      surface_offset_ = 0.0f;
      placement_loc_ = float3(scene.cursor.location);
    }
    else if (align_flag & GP_PROJECT_DEPTH_VIEW) {
      depth_ = DrawingPlacementDepth::Surface;
      if (align_flag & GP_PROJECT_DEPTH_ONLY_SELECTED) {
        use_project_only_selected_ = true;
      }
      surface_offset_ = scene.toolsettings->gpencil_surface_offset;
      /* Default to view placement with the object origin if we don't hit a surface. */
      placement_loc_ = layer_space_to_world_space_.location();
    }
    else if (align_flag & GP_PROJECT_DEPTH_STROKE) {
      depth_ = DrawingPlacementDepth::NearestStroke;
      surface_offset_ = 0.0f;
      /* Default to view placement with the object origin if we don't hit a stroke. */
      placement_loc_ = layer_space_to_world_space_.location();
    }
    else {
      depth_ = DrawingPlacementDepth::ObjectOrigin;
      surface_offset_ = 0.0f;
      placement_loc_ = layer_space_to_world_space_.location();
    }
  }
  else {
    depth_ = DrawingPlacementDepth::ObjectOrigin;
    surface_offset_ = 0.0f;
    placement_loc_ = float3(0.0f);
  }
 
  if (plane_ != DrawingPlacementPlane::View) {
    plane_from_point_normal_v3(placement_plane_, placement_loc_, placement_normal_);
  }
}
 
DrawingPlacement::DrawingPlacement(const Scene &scene,
                                   const ARegion &region,
                                   const View3D &view3d,
                                   const Object &eval_object,
                                   const bke::greasepencil::Layer *layer,
                                   const ReprojectMode reproject_mode,
                                   const float surface_offset,
                                   ViewDepths *view_depths)
    : region_(&region),
      view3d_(&view3d),
      depth_cache_(view_depths),
      surface_offset_(surface_offset)
{
  layer_space_to_world_space_ = (layer != nullptr) ? layer->to_world_space(eval_object) :
                                                     eval_object.object_to_world();
  world_space_to_layer_space_ = math::invert(layer_space_to_world_space_);
  /* Initialize DrawingPlacementPlane from mode. */
  switch (reproject_mode) {
    case ReprojectMode::View:
      plane_ = DrawingPlacementPlane::View;
      break;
    case ReprojectMode::Front:
      plane_ = DrawingPlacementPlane::Front;
      placement_normal_ = float3(0, 1, 0);
      break;
    case ReprojectMode::Side:
      plane_ = DrawingPlacementPlane::Side;
      placement_normal_ = float3(1, 0, 0);
      break;
    case ReprojectMode::Top:
      plane_ = DrawingPlacementPlane::Top;
      placement_normal_ = float3(0, 0, 1);
      break;
    case ReprojectMode::Cursor: {
      plane_ = DrawingPlacementPlane::Cursor;
      placement_normal_ = scene.cursor.matrix<float3x3>() * float3(0, 0, 1);
      break;
    }
    default:
      break;
  }
 
  /* Account for layer transform. */
  if (!ELEM(reproject_mode, ReprojectMode::View, ReprojectMode::Cursor)) {
    /* Use the transpose inverse for normal. */
    placement_normal_ = math::transform_direction(math::transpose(world_space_to_layer_space_),
                                                  placement_normal_);
  }
 
  /* Initialize DrawingPlacementDepth from mode. */
  switch (reproject_mode) {
    case ReprojectMode::Cursor:
      depth_ = DrawingPlacementDepth::Cursor;
      surface_offset_ = 0.0f;
      placement_loc_ = float3(scene.cursor.location);
      break;
    case ReprojectMode::View:
      depth_ = DrawingPlacementDepth::ObjectOrigin;
      surface_offset_ = 0.0f;
      placement_loc_ = layer_space_to_world_space_.location();
      break;
    case ReprojectMode::Surface:
      depth_ = DrawingPlacementDepth::Surface;
      placement_loc_ = layer_space_to_world_space_.location();
      break;
    default:
      depth_ = DrawingPlacementDepth::ObjectOrigin;
      surface_offset_ = 0.0f;
      placement_loc_ = layer_space_to_world_space_.location();
      break;
  }
 
  if (plane_ != DrawingPlacementPlane::View) {
    plane_from_point_normal_v3(placement_plane_, placement_loc_, placement_normal_);
  }
}
 
DrawingPlacement::DrawingPlacement(const DrawingPlacement &other)
{
  region_ = other.region_;
  view3d_ = other.view3d_;
 
  depth_ = other.depth_;
  plane_ = other.plane_;
 
  if (other.depth_cache_ != nullptr) {
    depth_cache_ = static_cast<ViewDepths *>(MEM_dupallocN(other.depth_cache_));
    depth_cache_->depths = static_cast<float *>(MEM_dupallocN(other.depth_cache_->depths));
  }
  use_project_only_selected_ = other.use_project_only_selected_;
 
  surface_offset_ = other.surface_offset_;
 
  placement_loc_ = other.placement_loc_;
  placement_normal_ = other.placement_normal_;
  placement_plane_ = other.placement_plane_;
 
  layer_space_to_world_space_ = other.layer_space_to_world_space_;
  world_space_to_layer_space_ = other.world_space_to_layer_space_;
}
 
DrawingPlacement::DrawingPlacement(DrawingPlacement &&other)
{
  region_ = other.region_;
  view3d_ = other.view3d_;
 
  depth_ = other.depth_;
  plane_ = other.plane_;
 
  std::swap(depth_cache_, other.depth_cache_);
  use_project_only_selected_ = other.use_project_only_selected_;
 
  surface_offset_ = other.surface_offset_;
 
  placement_loc_ = other.placement_loc_;
  placement_normal_ = other.placement_normal_;
  placement_plane_ = other.placement_plane_;
 
  layer_space_to_world_space_ = other.layer_space_to_world_space_;
  world_space_to_layer_space_ = other.world_space_to_layer_space_;
}
 
DrawingPlacement &DrawingPlacement::operator=(const DrawingPlacement &other)
{
  if (this == &other) {
    return *this;
  }
  std::destroy_at(this);
  new (this) DrawingPlacement(other);
  return *this;
}
 
DrawingPlacement &DrawingPlacement::operator=(DrawingPlacement &&other)
{
  if (this == &other) {
    return *this;
  }
  std::destroy_at(this);
  new (this) DrawingPlacement(std::move(other));
  return *this;
}
 
DrawingPlacement::~DrawingPlacement()
{
  if (depth_cache_ != nullptr) {
    ED_view3d_depths_free(depth_cache_);
  }
}
 
bool DrawingPlacement::use_project_to_surface() const
{
  return depth_ == DrawingPlacementDepth::Surface;
}
 
bool DrawingPlacement::use_project_to_nearest_stroke() const
{
  return depth_ == DrawingPlacementDepth::NearestStroke;
}
 
void DrawingPlacement::cache_viewport_depths(Depsgraph *depsgraph, ARegion *region, View3D *view3d)
{
  eV3DDepthOverrideMode mode = V3D_DEPTH_GPENCIL_ONLY;
 
  if (use_project_to_surface()) {
    if (use_project_only_selected_) {
      mode = V3D_DEPTH_SELECTED_ONLY;
    }
    else {
      mode = V3D_DEPTH_NO_GPENCIL;
    }
  }
  ED_view3d_depth_override(depsgraph, region, view3d, nullptr, mode, false, &this->depth_cache_);
}
 
void DrawingPlacement::set_origin_to_nearest_stroke(const float2 co)
{
  BLI_assert(depth_cache_ != nullptr);
  float depth;
  if (ED_view3d_depth_read_cached(depth_cache_, int2(co), 4, &depth)) {
    float3 origin;
    ED_view3d_depth_unproject_v3(region_, int2(co), depth, origin);
 
    placement_loc_ = origin;
  }
  else {
    /* If nothing was hit, use origin. */
    placement_loc_ = layer_space_to_world_space_.location();
  }
  plane_from_point_normal_v3(placement_plane_, placement_loc_, placement_normal_);
}
 
float3 DrawingPlacement::project_depth(const float2 co) const
{
  float3 proj_point;
  float depth;
  if (depth_cache_ != nullptr && ED_view3d_depth_read_cached(depth_cache_, int2(co), 4, &depth)) {
    ED_view3d_depth_unproject_v3(region_, int2(co), depth, proj_point);
    float3 view_normal;
    ED_view3d_win_to_vector(region_, co, view_normal);
    proj_point -= view_normal * surface_offset_;
  }
  else {
    /* Fallback to `View` placement. */
    ED_view3d_win_to_3d(view3d_, region_, placement_loc_, co, proj_point);
  }
  return proj_point;
}
 
float3 DrawingPlacement::project(const float2 co) const
{
  float3 proj_point;
  if (depth_ == DrawingPlacementDepth::Surface) {
    /* Project using the viewport depth cache. */
    proj_point = this->project_depth(co);
  }
  else {
    if (plane_ == DrawingPlacementPlane::View) {
      ED_view3d_win_to_3d(view3d_, region_, placement_loc_, co, proj_point);
    }
    else {
      ED_view3d_win_to_3d_on_plane(region_, placement_plane_, co, false, proj_point);
    }
  }
  return math::transform_point(world_space_to_layer_space_, proj_point);
}
 
float3 DrawingPlacement::project_with_shift(const float2 co) const
{
  float3 proj_point;
  if (depth_ == DrawingPlacementDepth::Surface) {
    /* Project using the viewport depth cache. */
    proj_point = this->project_depth(co);
  }
  else {
    if (plane_ == DrawingPlacementPlane::View) {
      ED_view3d_win_to_3d_with_shift(view3d_, region_, placement_loc_, co, proj_point);
    }
    else {
      ED_view3d_win_to_3d_on_plane(region_, placement_plane_, co, false, proj_point);
    }
  }
  return math::transform_point(world_space_to_layer_space_, proj_point);
}
 
void DrawingPlacement::project(const Span<float2> src, MutableSpan<float3> dst) const
{
  threading::parallel_for(src.index_range(), 1024, [&](const IndexRange range) {
    for (const int i : range) {
      dst[i] = this->project(src[i]);
    }
  });
}
 
float3 DrawingPlacement::reproject(const float3 pos) const
{
  const float3 world_pos = math::transform_point(layer_space_to_world_space_, pos);
  float3 proj_point;
  if (depth_ == DrawingPlacementDepth::Surface) {
    /* First project the position into view space. */
    float2 co;
    if (ED_view3d_project_float_global(region_, world_pos, co, V3D_PROJ_TEST_NOP)) {
      /* Can't reproject the point. */
      return pos;
    }
    /* Project using the viewport depth cache. */
    proj_point = this->project_depth(co);
  }
  else {
    /* Reproject the point onto the `placement_plane_` from the current view. */
    RegionView3D *rv3d = static_cast<RegionView3D *>(region_->regiondata);
 
    float3 ray_no;
    if (rv3d->is_persp) {
      ray_no = math::normalize(world_pos - float3(rv3d->viewinv[3]));
    }
    else {
      ray_no = -float3(rv3d->viewinv[2]);
    }
    float4 plane;
    if (plane_ == DrawingPlacementPlane::View) {
      plane_from_point_normal_v3(plane, placement_loc_, rv3d->viewinv[2]);
    }
    else {
      plane = placement_plane_;
    }
 
    float lambda;
    if (isect_ray_plane_v3(world_pos, ray_no, plane, &lambda, false)) {
      proj_point = world_pos + ray_no * lambda;
    }
    else {
      return pos;
    }
  }
  return math::transform_point(world_space_to_layer_space_, proj_point);
}
 
void DrawingPlacement::reproject(const Span<float3> src, MutableSpan<float3> dst) const
{
  threading::parallel_for(src.index_range(), 1024, [&](const IndexRange range) {
    for (const int i : range) {
      dst[i] = this->reproject(src[i]);
    }
  });
}
 
float4x4 DrawingPlacement::to_world_space() const
{
  return layer_space_to_world_space_;
}
 
static float get_multi_frame_falloff(const int frame_number,
                                     const int center_frame,
                                     const int min_frame,
                                     const int max_frame,
                                     const CurveMapping *falloff_curve)
{
  if (falloff_curve == nullptr) {
    return 1.0f;
  }
 
  /* Frame right of the center frame. */
  if (frame_number > center_frame) {
    const float frame_factor = 0.5f * float(center_frame - min_frame) / (frame_number - min_frame);
    return BKE_curvemapping_evaluateF(falloff_curve, 0, frame_factor);
  }
  /* Frame left of the center frame. */
  if (frame_number < center_frame) {
    const float frame_factor = 0.5f * float(center_frame - frame_number) /
                               (max_frame - frame_number);
    return BKE_curvemapping_evaluateF(falloff_curve, 0, frame_factor + 0.5f);
  }
  /* Frame at center. */
  return BKE_curvemapping_evaluateF(falloff_curve, 0, 0.5f);
}
 
static std::pair<int, int> get_minmax_selected_frame_numbers(const GreasePencil &grease_pencil,
                                                             const int current_frame)
{
  using namespace blender::bke::greasepencil;
  int frame_min = current_frame;
  int frame_max = current_frame;
  Span<const Layer *> layers = grease_pencil.layers();
  for (const int layer_i : layers.index_range()) {
    const Layer &layer = *layers[layer_i];
    if (!layer.is_editable()) {
      continue;
    }
    for (const auto [frame_number, frame] : layer.frames().items()) {
      if (frame_number != current_frame && frame.is_selected()) {
        frame_min = math::min(frame_min, frame_number);
        frame_max = math::max(frame_max, frame_number);
      }
    }
  }
  return std::pair<int, int>(frame_min, frame_max);
}
 
static std::optional<int> get_frame_id(const bke::greasepencil::Layer &layer,
                                       const GreasePencilFrame &frame,
                                       const int frame_number,
                                       const int frame_index,
                                       const int current_frame,
                                       const int current_frame_index,
                                       const int last_frame,
                                       const int last_frame_index,
                                       const bool use_multi_frame_editing,
                                       const bool do_onion_skinning,
                                       const bool is_before_first,
                                       const GreasePencilOnionSkinningSettings onion_settings)
{
  if (use_multi_frame_editing) {
    if (frame.is_selected()) {
      if (do_onion_skinning) {
        return (frame_number < current_frame) ? -1 : 1;
      }
      return 0;
    }
    return {};
  }
  if (do_onion_skinning && layer.use_onion_skinning()) {
    /* Keyframe type filter. */
    if (onion_settings.filter != 0 && (onion_settings.filter & (1 << frame.type)) == 0) {
      return {};
    }
    /* Selected mode filter. */
    if (onion_settings.mode == GP_ONION_SKINNING_MODE_SELECTED && !frame.is_selected()) {
      return {};
    }
 
    int delta = 0;
    if (onion_settings.mode == GP_ONION_SKINNING_MODE_ABSOLUTE) {
      delta = frame_number - current_frame;
    }
    else {
      delta = frame_index - current_frame_index;
    }
 
    if (is_before_first) {
      delta++;
    }
    if ((onion_settings.flag & GP_ONION_SKINNING_SHOW_LOOP) != 0 &&
        (-delta > onion_settings.num_frames_before || delta > onion_settings.num_frames_after))
    {
      /* We wrap the value using the last frame and 0 as reference. */
      /* FIXME: This might not be good for animations not starting at 0. */
      int shift = 0;
      if (onion_settings.mode == GP_ONION_SKINNING_MODE_ABSOLUTE) {
        shift = last_frame;
      }
      else {
        shift = last_frame_index;
      }
      delta += (delta < 0) ? (shift + 1) : -(shift + 1);
    }
    /* Frame range filter. */
    if (ELEM(onion_settings.mode,
             GP_ONION_SKINNING_MODE_ABSOLUTE,
             GP_ONION_SKINNING_MODE_RELATIVE) &&
        (-delta > onion_settings.num_frames_before || delta > onion_settings.num_frames_after))
    {
      return {};
    }
 
    return delta;
  }
  return {};
}
 
static Array<std::pair<int, int>> get_visible_frames_for_layer(
    const GreasePencil &grease_pencil,
    const bke::greasepencil::Layer &layer,
    const int current_frame,
    const bool use_multi_frame_editing,
    const bool do_onion_skinning)
{
  GreasePencilOnionSkinningSettings onion_settings = grease_pencil.onion_skinning_settings;
  Vector<std::pair<int, int>> frame_numbers;
  const Span<int> sorted_keys = layer.sorted_keys();
  if (sorted_keys.is_empty()) {
    return {};
  }
  const int current_frame_index = std::max(layer.sorted_keys_index_at(current_frame), 0);
  const int last_frame = sorted_keys.last();
  const int last_frame_index = sorted_keys.index_range().last();
  const bool is_before_first = (current_frame < sorted_keys.first());
  const std::optional<int> current_start_frame = layer.start_frame_at(current_frame);
  for (const int frame_i : sorted_keys.index_range()) {
    const int frame_number = sorted_keys[frame_i];
    if (current_start_frame && *current_start_frame == frame_number) {
      continue;
    }
    const GreasePencilFrame &frame = layer.frames().lookup(frame_number);
    const std::optional<int> frame_id = get_frame_id(layer,
                                                     frame,
                                                     frame_number,
                                                     frame_i,
                                                     current_frame,
                                                     current_frame_index,
                                                     last_frame,
                                                     last_frame_index,
                                                     use_multi_frame_editing,
                                                     do_onion_skinning,
                                                     is_before_first,
                                                     onion_settings);
    if (!frame_id.has_value()) {
      /* Drawing on this frame is not visible. */
      continue;
    }
 
    frame_numbers.append({frame_number, *frame_id});
  }
 
  frame_numbers.append({current_frame, 0});
 
  return frame_numbers.as_span();
}
 
static Array<int> get_editable_frames_for_layer(const GreasePencil &grease_pencil,
                                                const bke::greasepencil::Layer &layer,
                                                const int current_frame,
                                                const bool use_multi_frame_editing)
{
  using namespace blender::bke::greasepencil;
  Vector<int> frame_numbers;
  Set<const Drawing *> added_drawings;
  if (use_multi_frame_editing) {
    const Drawing *current_drawing = grease_pencil.get_drawing_at(layer, current_frame);
    for (const auto [frame_number, frame] : layer.frames().items()) {
      if (!frame.is_selected()) {
        continue;
      }
      frame_numbers.append(frame_number);
      added_drawings.add(grease_pencil.get_drawing_at(layer, frame_number));
    }
    if (added_drawings.contains(current_drawing)) {
      return frame_numbers.as_span();
    }
  }
 
  frame_numbers.append(current_frame);
  return frame_numbers.as_span();
}
 
Vector<MutableDrawingInfo> retrieve_editable_drawings(const Scene &scene,
                                                      GreasePencil &grease_pencil)
{
  using namespace blender::bke::greasepencil;
  const int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
 
  Vector<MutableDrawingInfo> editable_drawings;
  Span<const Layer *> layers = grease_pencil.layers();
  for (const int layer_i : layers.index_range()) {
    const Layer &layer = *layers[layer_i];
    if (!layer.is_editable()) {
      continue;
    }
    const Array<int> frame_numbers = get_editable_frames_for_layer(
        grease_pencil, layer, current_frame, use_multi_frame_editing);
    for (const int frame_number : frame_numbers) {
      if (Drawing *drawing = grease_pencil.get_editable_drawing_at(layer, frame_number)) {
        editable_drawings.append({*drawing, layer_i, frame_number, 1.0f});
      }
    }
  }
 
  return editable_drawings;
}
 
Vector<MutableDrawingInfo> retrieve_editable_drawings_with_falloff(const Scene &scene,
                                                                   GreasePencil &grease_pencil)
{
  using namespace blender::bke::greasepencil;
  const int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
  const bool use_multi_frame_falloff = use_multi_frame_editing &&
                                       (toolsettings->gp_sculpt.flag &
                                        GP_SCULPT_SETT_FLAG_FRAME_FALLOFF) != 0;
  int center_frame;
  std::pair<int, int> minmax_frame;
  if (use_multi_frame_falloff) {
    BKE_curvemapping_init(toolsettings->gp_sculpt.cur_falloff);
    minmax_frame = get_minmax_selected_frame_numbers(grease_pencil, current_frame);
    center_frame = math::clamp(current_frame, minmax_frame.first, minmax_frame.second);
  }
 
  Vector<MutableDrawingInfo> editable_drawings;
  Span<const Layer *> layers = grease_pencil.layers();
  for (const int layer_i : layers.index_range()) {
    const Layer &layer = *layers[layer_i];
    if (!layer.is_editable()) {
      continue;
    }
    const Array<int> frame_numbers = get_editable_frames_for_layer(
        grease_pencil, layer, current_frame, use_multi_frame_editing);
    for (const int frame_number : frame_numbers) {
      if (Drawing *drawing = grease_pencil.get_editable_drawing_at(layer, frame_number)) {
        const float falloff = use_multi_frame_falloff ?
                                  get_multi_frame_falloff(frame_number,
                                                          center_frame,
                                                          minmax_frame.first,
                                                          minmax_frame.second,
                                                          toolsettings->gp_sculpt.cur_falloff) :
                                  1.0f;
        editable_drawings.append({*drawing, layer_i, frame_number, falloff});
      }
    }
  }
 
  return editable_drawings;
}
 
Array<Vector<MutableDrawingInfo>> retrieve_editable_drawings_grouped_per_frame(
    const Scene &scene, GreasePencil &grease_pencil)
{
  using namespace blender::bke::greasepencil;
  int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
  const bool use_multi_frame_falloff = use_multi_frame_editing &&
                                       (toolsettings->gp_sculpt.flag &
                                        GP_SCULPT_SETT_FLAG_FRAME_FALLOFF) != 0;
  if (use_multi_frame_falloff) {
    BKE_curvemapping_init(toolsettings->gp_sculpt.cur_falloff);
  }
 
  /* Get a set of unique frame numbers with editable drawings on them. */
  VectorSet<int> selected_frames;
  int frame_min = current_frame, frame_max = current_frame;
  Span<const Layer *> layers = grease_pencil.layers();
  if (use_multi_frame_editing) {
    for (const int layer_i : layers.index_range()) {
      const Layer &layer = *layers[layer_i];
      if (!layer.is_editable()) {
        continue;
      }
      for (const auto [frame_number, frame] : layer.frames().items()) {
        if (frame_number != current_frame && frame.is_selected()) {
          selected_frames.add(frame_number);
          frame_min = math::min(frame_min, frame_number);
          frame_max = math::max(frame_max, frame_number);
        }
      }
    }
  }
  selected_frames.add(current_frame);
 
  /* Get multi frame falloff factor per selected frame. */
  Array<float> falloff_per_selected_frame(selected_frames.size(), 1.0f);
  if (use_multi_frame_falloff) {
    int frame_group = 0;
    for (const int frame_number : selected_frames) {
      falloff_per_selected_frame[frame_group] = get_multi_frame_falloff(
          frame_number, current_frame, frame_min, frame_max, toolsettings->gp_sculpt.cur_falloff);
      frame_group++;
    }
  }
 
  /* Get drawings grouped per frame. */
  Array<Vector<MutableDrawingInfo>> drawings_grouped_per_frame(selected_frames.size());
  Set<const Drawing *> added_drawings;
  for (const int layer_i : layers.index_range()) {
    const Layer &layer = *layers[layer_i];
    if (!layer.is_editable()) {
      continue;
    }
    /* In multi frame editing mode, add drawings at selected frames. */
    if (use_multi_frame_editing) {
      for (const auto [frame_number, frame] : layer.frames().items()) {
        Drawing *drawing = grease_pencil.get_editable_drawing_at(layer, frame_number);
        if (!frame.is_selected() || drawing == nullptr || added_drawings.contains(drawing)) {
          continue;
        }
        const int frame_group = selected_frames.index_of(frame_number);
        drawings_grouped_per_frame[frame_group].append(
            {*drawing, layer_i, frame_number, falloff_per_selected_frame[frame_group]});
        added_drawings.add_new(drawing);
      }
    }
 
    /* Add drawing at current frame. */
    Drawing *current_drawing = grease_pencil.get_drawing_at(layer, current_frame);
    if (current_drawing != nullptr && !added_drawings.contains(current_drawing)) {
      const int frame_group = selected_frames.index_of(current_frame);
      drawings_grouped_per_frame[frame_group].append(
          {*current_drawing, layer_i, current_frame, falloff_per_selected_frame[frame_group]});
      added_drawings.add_new(current_drawing);
    }
  }
 
  return drawings_grouped_per_frame;
}
 
Vector<MutableDrawingInfo> retrieve_editable_drawings_from_layer(
    const Scene &scene,
    GreasePencil &grease_pencil,
    const blender::bke::greasepencil::Layer &layer)
{
  using namespace blender::bke::greasepencil;
  const int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
  const int layer_index = *grease_pencil.get_layer_index(layer);
 
  Vector<MutableDrawingInfo> editable_drawings;
  const Array<int> frame_numbers = get_editable_frames_for_layer(
      grease_pencil, layer, current_frame, use_multi_frame_editing);
  for (const int frame_number : frame_numbers) {
    if (Drawing *drawing = grease_pencil.get_editable_drawing_at(layer, frame_number)) {
      editable_drawings.append({*drawing, layer_index, frame_number, 1.0f});
    }
  }
 
  return editable_drawings;
}
 
Vector<MutableDrawingInfo> retrieve_editable_drawings_from_layer_with_falloff(
    const Scene &scene,
    GreasePencil &grease_pencil,
    const blender::bke::greasepencil::Layer &layer)
{
  using namespace blender::bke::greasepencil;
  const int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
  const bool use_multi_frame_falloff = use_multi_frame_editing &&
                                       (toolsettings->gp_sculpt.flag &
                                        GP_SCULPT_SETT_FLAG_FRAME_FALLOFF) != 0;
  const int layer_index = *grease_pencil.get_layer_index(layer);
  int center_frame;
  std::pair<int, int> minmax_frame;
  if (use_multi_frame_falloff) {
    BKE_curvemapping_init(toolsettings->gp_sculpt.cur_falloff);
    minmax_frame = get_minmax_selected_frame_numbers(grease_pencil, current_frame);
    center_frame = math::clamp(current_frame, minmax_frame.first, minmax_frame.second);
  }
 
  Vector<MutableDrawingInfo> editable_drawings;
  const Array<int> frame_numbers = get_editable_frames_for_layer(
      grease_pencil, layer, current_frame, use_multi_frame_editing);
  for (const int frame_number : frame_numbers) {
    if (Drawing *drawing = grease_pencil.get_editable_drawing_at(layer, frame_number)) {
      const float falloff = use_multi_frame_falloff ?
                                get_multi_frame_falloff(frame_number,
                                                        center_frame,
                                                        minmax_frame.first,
                                                        minmax_frame.second,
                                                        toolsettings->gp_sculpt.cur_falloff) :
                                1.0f;
      editable_drawings.append({*drawing, layer_index, frame_number, falloff});
    }
  }
 
  return editable_drawings;
}
 
Vector<DrawingInfo> retrieve_visible_drawings(const Scene &scene,
                                              const GreasePencil &grease_pencil,
                                              const bool do_onion_skinning)
{
  using namespace blender::bke::greasepencil;
  const int current_frame = scene.r.cfra;
  const ToolSettings *toolsettings = scene.toolsettings;
  const bool use_multi_frame_editing = (toolsettings->gpencil_flags &
                                        GP_USE_MULTI_FRAME_EDITING) != 0;
 
  Vector<DrawingInfo> visible_drawings;
  Span<const Layer *> layers = grease_pencil.layers();
  for (const int layer_i : layers.index_range()) {
    const Layer &layer = *layers[layer_i];
    if (!layer.is_visible()) {
      continue;
    }
    const Array<std::pair<int, int>> frames = get_visible_frames_for_layer(
        grease_pencil, layer, current_frame, use_multi_frame_editing, do_onion_skinning);
    for (const auto &[frame_number, onion_id] : frames) {
      if (const Drawing *drawing = grease_pencil.get_drawing_at(layer, frame_number)) {
        visible_drawings.append({*drawing, layer_i, frame_number, onion_id});
      }
    }
  }
 
  return visible_drawings;
}
 
static VectorSet<int> get_editable_material_indices(Object &object)
{
  BLI_assert(object.type == OB_GREASE_PENCIL);
  VectorSet<int> editable_material_indices;
  for (const int mat_i : IndexRange(object.totcol)) {
    Material *material = BKE_object_material_get(&object, mat_i + 1);
    /* The editable materials are unlocked and not hidden. */
    if (material != nullptr && material->gp_style != nullptr &&
        (material->gp_style->flag & GP_MATERIAL_LOCKED) == 0 &&
        (material->gp_style->flag & GP_MATERIAL_HIDE) == 0)
    {
      editable_material_indices.add_new(mat_i);
    }
  }
  return editable_material_indices;
}
 
static VectorSet<int> get_hidden_material_indices(Object &object)
{
  BLI_assert(object.type == OB_GREASE_PENCIL);
  VectorSet<int> hidden_material_indices;
  for (const int mat_i : IndexRange(object.totcol)) {
    Material *material = BKE_object_material_get(&object, mat_i + 1);
    if (material != nullptr && material->gp_style != nullptr &&
        (material->gp_style->flag & GP_MATERIAL_HIDE) != 0)
    {
      hidden_material_indices.add_new(mat_i);
    }
  }
  return hidden_material_indices;
}
 
static VectorSet<int> get_fill_material_indices(Object &object)
{
  BLI_assert(object.type == OB_GREASE_PENCIL);
  VectorSet<int> fill_material_indices;
  for (const int mat_i : IndexRange(object.totcol)) {
    Material *material = BKE_object_material_get(&object, mat_i + 1);
    if (material != nullptr && material->gp_style != nullptr &&
        (material->gp_style->flag & GP_MATERIAL_FILL_SHOW) != 0)
    {
      fill_material_indices.add_new(mat_i);
    }
  }
  return fill_material_indices;
}
 
IndexMask retrieve_editable_strokes(Object &object,
                                    const bke::greasepencil::Drawing &drawing,
                                    int layer_index,
                                    IndexMaskMemory &memory)
{
  using namespace blender;
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange curves_range = curves.curves_range();
 
  if (object.totcol == 0) {
    return IndexMask(curves_range);
  }
 
  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(object.data);
  const bke::greasepencil::Layer &layer = *grease_pencil.layers()[layer_index];
 
  /* If we're not using material locking, the entire curves range is editable. */
  if (layer.ignore_locked_materials()) {
    return IndexMask(curves_range);
  }
 
  /* Get all the editable material indices */
  VectorSet<int> editable_material_indices = get_editable_material_indices(object);
  if (editable_material_indices.is_empty()) {
    return {};
  }
 
  const bke::AttributeAccessor attributes = curves.attributes();
  const VArray<int> materials = *attributes.lookup<int>("material_index", bke::AttrDomain::Curve);
  if (!materials) {
    /* If the attribute does not exist then the default is the first material. */
    if (editable_material_indices.contains(0)) {
      return curves_range;
    }
    return {};
  }
  /* Get all the strokes that have their material unlocked. */
  return IndexMask::from_predicate(
      curves_range, GrainSize(4096), memory, [&](const int64_t curve_i) {
        return editable_material_indices.contains(materials[curve_i]);
      });
}
 
IndexMask retrieve_editable_fill_strokes(Object &object,
                                         const bke::greasepencil::Drawing &drawing,
                                         int layer_index,
                                         IndexMaskMemory &memory)
{
  using namespace blender;
  const IndexMask editable_strokes = retrieve_editable_strokes(
      object, drawing, layer_index, memory);
  if (editable_strokes.is_empty()) {
    return {};
  }
 
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange curves_range = curves.curves_range();
 
  const bke::AttributeAccessor attributes = curves.attributes();
  const VArray<int> materials = *attributes.lookup<int>("material_index", bke::AttrDomain::Curve);
  const VectorSet<int> fill_material_indices = get_fill_material_indices(object);
  if (!materials) {
    /* If the attribute does not exist then the default is the first material. */
    if (editable_strokes.contains(0) && fill_material_indices.contains(0)) {
      return curves_range;
    }
    return {};
  }
  const IndexMask fill_strokes = IndexMask::from_predicate(
      curves_range, GrainSize(4096), memory, [&](const int64_t curve_i) {
        const int material_index = materials[curve_i];
        return fill_material_indices.contains(material_index);
      });
  return IndexMask::from_intersection(editable_strokes, fill_strokes, memory);
}
 
IndexMask retrieve_editable_strokes_by_material(Object &object,
                                                const bke::greasepencil::Drawing &drawing,
                                                const int mat_i,
                                                IndexMaskMemory &memory)
{
  using namespace blender;
 
  /* Get all the editable material indices */
  VectorSet<int> editable_material_indices = get_editable_material_indices(object);
  if (editable_material_indices.is_empty()) {
    return {};
  }
 
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange curves_range = drawing.strokes().curves_range();
  const bke::AttributeAccessor attributes = curves.attributes();
 
  const VArray<int> materials = *attributes.lookup<int>("material_index", bke::AttrDomain::Curve);
  if (!materials) {
    /* If the attribute does not exist then the default is the first material. */
    if (editable_material_indices.contains(0)) {
      return curves_range;
    }
    return {};
  }
  /* Get all the strokes that share the same material and have it unlocked. */
  return IndexMask::from_predicate(
      curves_range, GrainSize(4096), memory, [&](const int64_t curve_i) {
        const int material_index = materials[curve_i];
        if (material_index == mat_i) {
          return editable_material_indices.contains(material_index);
        }
        return false;
      });
}
 
IndexMask retrieve_editable_points(Object &object,
                                   const bke::greasepencil::Drawing &drawing,
                                   int layer_index,
                                   IndexMaskMemory &memory)
{
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange points_range = curves.points_range();
 
  if (object.totcol == 0) {
    return IndexMask(points_range);
  }
 
  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(object.data);
  const bke::greasepencil::Layer &layer = *grease_pencil.layers()[layer_index];
 
  /* If we're not using material locking, the entire points range is editable. */
  if (layer.ignore_locked_materials()) {
    return IndexMask(points_range);
  }
 
  /* Get all the editable material indices */
  VectorSet<int> editable_material_indices = get_editable_material_indices(object);
  if (editable_material_indices.is_empty()) {
    return {};
  }
 
  /* Propagate the material index to the points. */
  const bke::AttributeAccessor attributes = curves.attributes();
  const VArray<int> materials = *attributes.lookup<int>("material_index", bke::AttrDomain::Point);
  if (!materials) {
    /* If the attribute does not exist then the default is the first material. */
    if (editable_material_indices.contains(0)) {
      return points_range;
    }
    return {};
  }
  /* Get all the points that are part of a stroke with an unlocked material. */
  return IndexMask::from_predicate(
      points_range, GrainSize(4096), memory, [&](const int64_t point_i) {
        return editable_material_indices.contains(materials[point_i]);
      });
}
 
IndexMask retrieve_editable_elements(Object &object,
                                     const MutableDrawingInfo &info,
                                     const bke::AttrDomain selection_domain,
                                     IndexMaskMemory &memory)
{
 
  const bke::greasepencil::Drawing &drawing = info.drawing;
  if (selection_domain == bke::AttrDomain::Curve) {
    return ed::greasepencil::retrieve_editable_strokes(object, drawing, info.layer_index, memory);
  }
  else if (selection_domain == bke::AttrDomain::Point) {
    return ed::greasepencil::retrieve_editable_points(object, drawing, info.layer_index, memory);
  }
  return {};
}
 
IndexMask retrieve_visible_strokes(Object &object,
                                   const bke::greasepencil::Drawing &drawing,
                                   IndexMaskMemory &memory)
{
  using namespace blender;
 
  /* Get all the hidden material indices. */
  VectorSet<int> hidden_material_indices = get_hidden_material_indices(object);
 
  if (hidden_material_indices.is_empty()) {
    return drawing.strokes().curves_range();
  }
 
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange curves_range = drawing.strokes().curves_range();
  const bke::AttributeAccessor attributes = curves.attributes();
 
  /* Get all the strokes that have their material visible. */
  const VArray<int> materials = *attributes.lookup_or_default<int>(
      "material_index", bke::AttrDomain::Curve, 0);
  return IndexMask::from_predicate(
      curves_range, GrainSize(4096), memory, [&](const int64_t curve_i) {
        const int material_index = materials[curve_i];
        return !hidden_material_indices.contains(material_index);
      });
}
 
IndexMask retrieve_visible_points(Object &object,
                                  const bke::greasepencil::Drawing &drawing,
                                  IndexMaskMemory &memory)
{
  /* Get all the hidden material indices. */
  VectorSet<int> hidden_material_indices = get_hidden_material_indices(object);
 
  if (hidden_material_indices.is_empty()) {
    return drawing.strokes().points_range();
  }
 
  const bke::CurvesGeometry &curves = drawing.strokes();
  const IndexRange points_range = curves.points_range();
  const bke::AttributeAccessor attributes = curves.attributes();
 
  /* Propagate the material index to the points. */
  const VArray<int> materials = *attributes.lookup_or_default<int>(
      "material_index", bke::AttrDomain::Point, 0);
  if (const std::optional<int> single_material = materials.get_if_single()) {
    if (!hidden_material_indices.contains(*single_material)) {
      return points_range;
    }
    return {};
  }
 
  /* Get all the points that are part of a stroke with a visible material. */
  return IndexMask::from_predicate(
      points_range, GrainSize(4096), memory, [&](const int64_t point_i) {
        const int material_index = materials[point_i];
        return !hidden_material_indices.contains(material_index);
      });
}
 
IndexMask retrieve_visible_bezier_handle_points(Object &object,
                                                const bke::greasepencil::Drawing &drawing,
                                                const int layer_index,
                                                IndexMaskMemory &memory)
{
  const bke::CurvesGeometry &curves = drawing.strokes();
 
  if (!curves.has_curve_with_type(CURVE_TYPE_BEZIER)) {
    return IndexMask(0);
  }
 
  const Array<int> point_to_curve_map = curves.point_to_curve_map();
  const VArray<int8_t> types = curves.curve_types();
 
  const VArray<bool> selected_point = *curves.attributes().lookup_or_default<bool>(
      ".selection", bke::AttrDomain::Point, true);
  const VArray<bool> selected_left = *curves.attributes().lookup_or_default<bool>(
      ".selection_handle_left", bke::AttrDomain::Point, true);
  const VArray<bool> selected_right = *curves.attributes().lookup_or_default<bool>(
      ".selection_handle_right", bke::AttrDomain::Point, true);
 
  const IndexMask editable_points = ed::greasepencil::retrieve_editable_points(
      object, drawing, layer_index, memory);
 
  const IndexMask selected_points = IndexMask::from_predicate(
      curves.points_range(), GrainSize(4096), memory, [&](const int64_t point_i) {
        const bool is_selected = selected_point[point_i] || selected_left[point_i] ||
                                 selected_right[point_i];
        const bool is_bezier = types[point_to_curve_map[point_i]] == CURVE_TYPE_BEZIER;
        return is_selected && is_bezier;
      });
 
  return IndexMask::from_intersection(editable_points, selected_points, memory);
}
 
IndexMask retrieve_visible_bezier_handle_elements(Object &object,
                                                  const bke::greasepencil::Drawing &drawing,
                                                  const int layer_index,
                                                  const bke::AttrDomain selection_domain,
                                                  IndexMaskMemory &memory)
{
  if (selection_domain == bke::AttrDomain::Curve) {
    return ed::greasepencil::retrieve_editable_and_selected_strokes(
        object, drawing, layer_index, memory);
  }
  else if (selection_domain == bke::AttrDomain::Point) {
    return ed::greasepencil::retrieve_visible_bezier_handle_points(
        object, drawing, layer_index, memory);
  }
  return {};
}
 
IndexMask retrieve_editable_and_selected_strokes(Object &object,
                                                 const bke::greasepencil::Drawing &drawing,
                                                 int layer_index,
                                                 IndexMaskMemory &memory)
{
  using namespace blender;
  const bke::CurvesGeometry &curves = drawing.strokes();
 
  const IndexMask editable_strokes = retrieve_editable_strokes(
      object, drawing, layer_index, memory);
  const IndexMask selected_strokes = ed::curves::retrieve_selected_curves(curves, memory);
 
  return IndexMask::from_intersection(editable_strokes, selected_strokes, memory);
}
 
IndexMask retrieve_editable_and_selected_fill_strokes(Object &object,
                                                      const bke::greasepencil::Drawing &drawing,
                                                      int layer_index,
                                                      IndexMaskMemory &memory)
{
  using namespace blender;
  const bke::CurvesGeometry &curves = drawing.strokes();
 
  const IndexMask editable_strokes = retrieve_editable_fill_strokes(
      object, drawing, layer_index, memory);
  const IndexMask selected_strokes = ed::curves::retrieve_selected_curves(curves, memory);
 
  return IndexMask::from_intersection(editable_strokes, selected_strokes, memory);
}
 
IndexMask retrieve_editable_and_selected_points(Object &object,
                                                const bke::greasepencil::Drawing &drawing,
                                                int layer_index,
                                                IndexMaskMemory &memory)
{
  const bke::CurvesGeometry &curves = drawing.strokes();
 
  const IndexMask editable_points = retrieve_editable_points(object, drawing, layer_index, memory);
  const IndexMask selected_points = ed::curves::retrieve_selected_points(curves, memory);
 
  return IndexMask::from_intersection(editable_points, selected_points, memory);
}
 
IndexMask retrieve_editable_and_selected_elements(Object &object,
                                                  const bke::greasepencil::Drawing &drawing,
                                                  int layer_index,
                                                  const bke::AttrDomain selection_domain,
                                                  IndexMaskMemory &memory)
{
  if (selection_domain == bke::AttrDomain::Curve) {
    return ed::greasepencil::retrieve_editable_and_selected_strokes(
        object, drawing, layer_index, memory);
  }
  else if (selection_domain == bke::AttrDomain::Point) {
    return ed::greasepencil::retrieve_editable_and_selected_points(
        object, drawing, layer_index, memory);
  }
  return {};
}
 
Array<PointTransferData> compute_topology_change(
    const bke::CurvesGeometry &src,
    bke::CurvesGeometry &dst,
    const Span<Vector<PointTransferData>> src_to_dst_points,
    const bool keep_caps)
{
  const int src_curves_num = src.curves_num();
  const OffsetIndices<int> src_points_by_curve = src.points_by_curve();
  const VArray<bool> src_cyclic = src.cyclic();
 
  int dst_points_num = 0;
  for (const Vector<PointTransferData> &src_transfer_data : src_to_dst_points) {
    dst_points_num += src_transfer_data.size();
  }
  if (dst_points_num == 0) {
    dst.resize(0, 0);
    return Array<PointTransferData>(0);
  }
 
  /* Set the intersection parameters in the destination domain : a pair of int and float
   * numbers for which the integer is the index of the corresponding segment in the
   * source curves, and the float part is the (0,1) factor representing its position in
   * the segment.
   */
  Array<PointTransferData> dst_transfer_data(dst_points_num);
 
  Array<int> src_pivot_point(src_curves_num, -1);
  Array<int> dst_interm_curves_offsets(src_curves_num + 1, 0);
  int dst_point = -1;
  for (const int src_curve : src.curves_range()) {
    const IndexRange src_points = src_points_by_curve[src_curve];
 
    for (const int src_point : src_points) {
      for (const PointTransferData &dst_point_transfer : src_to_dst_points[src_point]) {
        if (dst_point_transfer.is_src_point) {
          dst_transfer_data[++dst_point] = dst_point_transfer;
          continue;
        }
 
        /* Add an intersection with the eraser and mark it as a cut. */
        dst_transfer_data[++dst_point] = dst_point_transfer;
 
        /* For cyclic curves, mark the pivot point as the last intersection with the eraser
         * that starts a new segment in the destination.
         */
        if (src_cyclic[src_curve] && dst_point_transfer.is_cut) {
          src_pivot_point[src_curve] = dst_point;
        }
      }
    }
    /* We store intermediate curve offsets represent an intermediate state of the
     * destination curves before cutting the curves at eraser's intersection. Thus, it
     * contains the same number of curves than in the source, but the offsets are
     * different, because points may have been added or removed. */
    dst_interm_curves_offsets[src_curve + 1] = dst_point + 1;
  }
 
  /* Cyclic curves. */
  Array<bool> src_now_cyclic(src_curves_num);
  threading::parallel_for(src.curves_range(), 4096, [&](const IndexRange src_curves) {
    for (const int src_curve : src_curves) {
      const int pivot_point = src_pivot_point[src_curve];
 
      if (pivot_point == -1) {
        /* Either the curve was not cyclic or it wasn't cut : no need to change it. */
        src_now_cyclic[src_curve] = src_cyclic[src_curve];
        continue;
      }
 
      /* A cyclic curve was cut :
       *  - this curve is not cyclic anymore,
       *  - and we have to shift points to keep the closing segment.
       */
      src_now_cyclic[src_curve] = false;
 
      const int dst_interm_first = dst_interm_curves_offsets[src_curve];
      const int dst_interm_last = dst_interm_curves_offsets[src_curve + 1];
      std::rotate(dst_transfer_data.begin() + dst_interm_first,
                  dst_transfer_data.begin() + pivot_point,
                  dst_transfer_data.begin() + dst_interm_last);
    }
  });
 
  /* Compute the destination curve offsets. */
  Vector<int> dst_curves_offset;
  Vector<int> dst_to_src_curve;
  dst_curves_offset.append(0);
  for (int src_curve : src.curves_range()) {
    const IndexRange dst_points(dst_interm_curves_offsets[src_curve],
                                dst_interm_curves_offsets[src_curve + 1] -
                                    dst_interm_curves_offsets[src_curve]);
    int length_of_current = 0;
 
    for (int dst_point : dst_points) {
 
      if ((length_of_current > 0) && dst_transfer_data[dst_point].is_cut) {
        /* This is the new first point of a curve. */
        dst_curves_offset.append(dst_point);
        dst_to_src_curve.append(src_curve);
        length_of_current = 0;
      }
      ++length_of_current;
    }
 
    if (length_of_current != 0) {
      /* End of a source curve. */
      dst_curves_offset.append(dst_points.one_after_last());
      dst_to_src_curve.append(src_curve);
    }
  }
  const int dst_curves_num = dst_curves_offset.size() - 1;
  if (dst_curves_num == 0) {
    dst.resize(0, 0);
    return dst_transfer_data;
  }
 
  /* Build destination curves geometry. */
  dst.resize(dst_points_num, dst_curves_num);
  array_utils::copy(dst_curves_offset.as_span(), dst.offsets_for_write());
  const OffsetIndices<int> dst_points_by_curve = dst.points_by_curve();
 
  /* Attributes. */
  const bke::AttributeAccessor src_attributes = src.attributes();
  bke::MutableAttributeAccessor dst_attributes = dst.attributes_for_write();
 
  /* Copy curves attributes. */
  bke::gather_attributes(src_attributes,
                         bke::AttrDomain::Curve,
                         bke::AttrDomain::Curve,
                         bke::attribute_filter_from_skip_ref({"cyclic"}),
                         dst_to_src_curve,
                         dst_attributes);
  if (src_cyclic.get_if_single().value_or(true)) {
    array_utils::gather(
        src_now_cyclic.as_span(), dst_to_src_curve.as_span(), dst.cyclic_for_write());
  }
 
  dst.update_curve_types();
 
  /* Display intersections with flat caps. */
  if (!keep_caps) {
    bke::SpanAttributeWriter<int8_t> dst_start_caps =
        dst_attributes.lookup_or_add_for_write_span<int8_t>("start_cap", bke::AttrDomain::Curve);
    bke::SpanAttributeWriter<int8_t> dst_end_caps =
        dst_attributes.lookup_or_add_for_write_span<int8_t>("end_cap", bke::AttrDomain::Curve);
 
    threading::parallel_for(dst.curves_range(), 4096, [&](const IndexRange dst_curves) {
      for (const int dst_curve : dst_curves) {
        const IndexRange dst_curve_points = dst_points_by_curve[dst_curve];
        const PointTransferData &start_point_transfer =
            dst_transfer_data[dst_curve_points.first()];
        const PointTransferData &end_point_transfer = dst_transfer_data[dst_curve_points.last()];
 
        if (start_point_transfer.is_cut) {
          dst_start_caps.span[dst_curve] = GP_STROKE_CAP_TYPE_FLAT;
        }
        /* The is_cut flag does not work for end points, but any end point that isn't the source
         * point must also be a cut. */
        if (!end_point_transfer.is_src_end_point()) {
          dst_end_caps.span[dst_curve] = GP_STROKE_CAP_TYPE_FLAT;
        }
      }
    });
 
    dst_start_caps.finish();
    dst_end_caps.finish();
  }
 
  /* Copy/Interpolate point attributes. */
  for (bke::AttributeTransferData &attribute : bke::retrieve_attributes_for_transfer(
           src_attributes, dst_attributes, ATTR_DOMAIN_MASK_POINT))
  {
    bke::attribute_math::convert_to_static_type(attribute.dst.span.type(), [&](auto dummy) {
      using T = decltype(dummy);
      auto src_attr = attribute.src.typed<T>();
      auto dst_attr = attribute.dst.span.typed<T>();
 
      threading::parallel_for(dst.points_range(), 4096, [&](const IndexRange dst_points) {
        for (const int dst_point : dst_points) {
          const PointTransferData &point_transfer = dst_transfer_data[dst_point];
          if (point_transfer.is_src_point) {
            dst_attr[dst_point] = src_attr[point_transfer.src_point];
          }
          else {
            dst_attr[dst_point] = bke::attribute_math::mix2<T>(
                point_transfer.factor,
                src_attr[point_transfer.src_point],
                src_attr[point_transfer.src_next_point]);
          }
        }
      });
 
      attribute.dst.finish();
    });
  }
 
  return dst_transfer_data;
}
 
static float pixel_radius_to_world_space_radius(const RegionView3D *rv3d,
                                                const ARegion *region,
                                                const float3 center,
                                                const float4x4 to_world,
                                                const float pixel_radius)
{
  const float2 xy_delta = float2(pixel_radius, 0.0f);
  const float3 loc = math::transform_point(to_world, center);
 
  const float zfac = ED_view3d_calc_zfac(rv3d, loc);
  float3 delta;
  ED_view3d_win_to_delta(region, xy_delta, zfac, delta);
 
  const float scale = math::length(
      math::transform_direction(to_world, float3(math::numbers::inv_sqrt3)));
 
  return math::safe_divide(math::length(delta), scale);
}
 
static float brush_radius_at_location(const RegionView3D *rv3d,
                                      const ARegion *region,
                                      const Brush *brush,
                                      const float3 location,
                                      const float4x4 to_world)
{
  if ((brush->flag & BRUSH_LOCK_SIZE) == 0) {
    return pixel_radius_to_world_space_radius(rv3d, region, location, to_world, brush->size);
  }
  return brush->unprojected_radius;
}
 
float radius_from_input_sample(const RegionView3D *rv3d,
                               const ARegion *region,
                               const Brush *brush,
                               const float pressure,
                               const float3 location,
                               const float4x4 to_world,
                               const BrushGpencilSettings *settings)
{
  float radius = brush_radius_at_location(rv3d, region, brush, location, to_world);
  if (BKE_brush_use_size_pressure(brush)) {
    radius *= BKE_curvemapping_evaluateF(settings->curve_sensitivity, 0, pressure);
  }
  return radius;
}
 
float opacity_from_input_sample(const float pressure,
                                const Brush *brush,
                                const BrushGpencilSettings *settings)
{
  float opacity = brush->alpha;
  if (BKE_brush_use_alpha_pressure(brush)) {
    opacity *= BKE_curvemapping_evaluateF(settings->curve_strength, 0, pressure);
  }
  return opacity;
}
 
int grease_pencil_draw_operator_invoke(bContext *C,
                                       wmOperator *op,
                                       const bool use_duplicate_previous_key)
{
  const Scene *scene = CTX_data_scene(C);
  const Object *object = CTX_data_active_object(C);
  if (!object || object->type != OB_GREASE_PENCIL) {
    return OPERATOR_CANCELLED;
  }
 
  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(object->data);
  if (!grease_pencil.has_active_layer()) {
    BKE_report(op->reports, RPT_ERROR, "No active Grease Pencil layer");
    return OPERATOR_CANCELLED;
  }
 
  const Paint *paint = BKE_paint_get_active_from_context(C);
  const Brush *brush = BKE_paint_brush_for_read(paint);
  if (brush == nullptr) {
    return OPERATOR_CANCELLED;
  }
 
  bke::greasepencil::Layer &active_layer = *grease_pencil.get_active_layer();
 
  if (!active_layer.is_editable()) {
    BKE_report(op->reports, RPT_ERROR, "Active layer is locked or hidden");
    return OPERATOR_CANCELLED;
  }
 
  /* Ensure a drawing at the current keyframe. */
  bool inserted_keyframe = false;
  if (!ed::greasepencil::ensure_active_keyframe(
          *scene, grease_pencil, active_layer, use_duplicate_previous_key, inserted_keyframe))
  {
    BKE_report(op->reports, RPT_ERROR, "No Grease Pencil frame to draw on");
    return OPERATOR_CANCELLED;
  }
  if (inserted_keyframe) {
    WM_event_add_notifier(C, NC_GPENCIL | NA_EDITED, nullptr);
  }
  return OPERATOR_RUNNING_MODAL;
}
 
float4x2 calculate_texture_space(const Scene *scene,
                                 const ARegion *region,
                                 const float2 &mouse,
                                 const DrawingPlacement &placement)
{
  float3 u_dir;
  float3 v_dir;
  /* Set the texture space origin to be the first point. */
  float3 origin = placement.project(mouse);
  /* Align texture with the drawing plane. */
  switch (scene->toolsettings->gp_sculpt.lock_axis) {
    case GP_LOCKAXIS_VIEW:
      u_dir = math::normalize(placement.project(float2(region->winx, 0.0f) + mouse) - origin);
      v_dir = math::normalize(placement.project(float2(0.0f, region->winy) + mouse) - origin);
      break;
    case GP_LOCKAXIS_Y:
      u_dir = float3(1.0f, 0.0f, 0.0f);
      v_dir = float3(0.0f, 0.0f, 1.0f);
      break;
    case GP_LOCKAXIS_X:
      u_dir = float3(0.0f, 1.0f, 0.0f);
      v_dir = float3(0.0f, 0.0f, 1.0f);
      break;
    case GP_LOCKAXIS_Z:
      u_dir = float3(1.0f, 0.0f, 0.0f);
      v_dir = float3(0.0f, 1.0f, 0.0f);
      break;
    case GP_LOCKAXIS_CURSOR: {
      const float3x3 mat = scene->cursor.matrix<float3x3>();
      u_dir = mat * float3(1.0f, 0.0f, 0.0f);
      v_dir = mat * float3(0.0f, 1.0f, 0.0f);
      origin = float3(scene->cursor.location);
      break;
    }
  }
 
  return math::transpose(float2x4(float4(u_dir, -math::dot(u_dir, origin)),
                                  float4(v_dir, -math::dot(v_dir, origin))));
}
 
GreasePencil *from_context(bContext &C)
{
  GreasePencil *grease_pencil = static_cast<GreasePencil *>(
      CTX_data_pointer_get_type(&C, "grease_pencil", &RNA_GreasePencilv3).data);
 
  if (grease_pencil == nullptr) {
    Object *object = CTX_data_active_object(&C);
    if (object && object->type == OB_GREASE_PENCIL) {
      grease_pencil = static_cast<GreasePencil *>(object->data);
    }
  }
  return grease_pencil;
}
 
}  // namespace blender::ed::greasepencil