/* SPDX-License-Identifier: GPL-2.0-or-later
 * Copyright 2020 Blender Foundation. All rights reserved. */

/** \file
 * \ingroup edsculpt
 */

#include "MEM_guardedalloc.h"

#include "BLI_blenlib.h"
#include "BLI_math.h"

#include "BLT_translation.h"

#include "DNA_mesh_types.h"

#include "BKE_context.h"
#include "BKE_paint.h"
#include "BKE_pbvh.h"
#include "BKE_screen.h"

#include "DEG_depsgraph.h"

#include "GPU_immediate.h"
#include "GPU_immediate_util.h"
#include "GPU_matrix.h"
#include "GPU_state.h"

#include "WM_api.h"
#include "WM_types.h"

#include "ED_screen.h"
#include "ED_sculpt.h"
#include "ED_space_api.h"
#include "ED_view3d.h"
#include "sculpt_intern.h"

#include "RNA_access.h"
#include "RNA_define.h"

#include <math.h>
#include <stdlib.h>

/* -------------------------------------------------------------------- */
/** \name Internal Utilities
 * \{ */

typedef struct {
  const float *ray_start;
  bool hit;
  float depth;
  float edge_length;

  struct IsectRayPrecalc isect_precalc;
} SculptDetailRaycastData;

static bool sculpt_and_constant_or_manual_detail_poll(bContext *C)
{
  Object *ob = CTX_data_active_object(C);
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;

  return SCULPT_mode_poll(C) && ob->sculpt->bm &&
         (sd->flags & (SCULPT_DYNTOPO_DETAIL_CONSTANT | SCULPT_DYNTOPO_DETAIL_MANUAL));
}

static bool sculpt_and_dynamic_topology_poll(bContext *C)
{
  Object *ob = CTX_data_active_object(C);

  return SCULPT_mode_poll(C) && ob->sculpt->bm;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Detail Flood Fill
 * \{ */

static int sculpt_detail_flood_fill_exec(bContext *C, wmOperator *UNUSED(op))
{
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;
  Object *ob = CTX_data_active_object(C);
  SculptSession *ss = ob->sculpt;
  float size;
  float bb_min[3], bb_max[3], center[3], dim[3];
  int totnodes;
  PBVHNode **nodes;

  BKE_pbvh_search_gather(ss->pbvh, NULL, NULL, &nodes, &totnodes);

  if (!totnodes) {
    return OPERATOR_CANCELLED;
  }

  for (int i = 0; i < totnodes; i++) {
    BKE_pbvh_node_mark_topology_update(nodes[i]);
  }
  /* Get the bounding box, its center and size. */
  BKE_pbvh_bounding_box(ob->sculpt->pbvh, bb_min, bb_max);
  add_v3_v3v3(center, bb_min, bb_max);
  mul_v3_fl(center, 0.5f);
  sub_v3_v3v3(dim, bb_max, bb_min);
  size = max_fff(dim[0], dim[1], dim[2]);

  /* Update topology size. */
  float object_space_constant_detail = 1.0f / (sd->constant_detail * mat4_to_scale(ob->obmat));
  BKE_pbvh_bmesh_detail_size_set(ss->pbvh, object_space_constant_detail);

  SCULPT_undo_push_begin(ob, "Dynamic topology flood fill");
  SCULPT_undo_push_node(ob, NULL, SCULPT_UNDO_COORDS);

  while (BKE_pbvh_bmesh_update_topology(
      ss->pbvh, PBVH_Collapse | PBVH_Subdivide, center, NULL, size, false, false)) {
    for (int i = 0; i < totnodes; i++) {
      BKE_pbvh_node_mark_topology_update(nodes[i]);
    }
  }

  MEM_SAFE_FREE(nodes);
  SCULPT_undo_push_end(ob);

  /* Force rebuild of PBVH for better BB placement. */
  SCULPT_pbvh_clear(ob);
  /* Redraw. */
  WM_event_add_notifier(C, NC_OBJECT | ND_DRAW, ob);

  return OPERATOR_FINISHED;
}

void SCULPT_OT_detail_flood_fill(wmOperatorType *ot)
{
  /* Identifiers. */
  ot->name = "Detail Flood Fill";
  ot->idname = "SCULPT_OT_detail_flood_fill";
  ot->description = "Flood fill the mesh with the selected detail setting";

  /* API callbacks. */
  ot->exec = sculpt_detail_flood_fill_exec;
  ot->poll = sculpt_and_constant_or_manual_detail_poll;

  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Sample Detail Size
 * \{ */

typedef enum eSculptSampleDetailModeTypes {
  SAMPLE_DETAIL_DYNTOPO = 0,
  SAMPLE_DETAIL_VOXEL = 1,
} eSculptSampleDetailModeTypes;

static EnumPropertyItem prop_sculpt_sample_detail_mode_types[] = {
    {SAMPLE_DETAIL_DYNTOPO, "DYNTOPO", 0, "Dyntopo", "Sample dyntopo detail"},
    {SAMPLE_DETAIL_VOXEL, "VOXEL", 0, "Voxel", "Sample mesh voxel size"},
    {0, NULL, 0, NULL, NULL},
};

static void sample_detail_voxel(bContext *C, ViewContext *vc, const int mval[2])
{
  Depsgraph *depsgraph = CTX_data_depsgraph_pointer(C);
  Object *ob = vc->obact;
  Mesh *mesh = ob->data;

  SculptSession *ss = ob->sculpt;
  SculptCursorGeometryInfo sgi;
  SCULPT_vertex_random_access_ensure(ss);

  /* Update the active vertex. */
  const float mval_fl[2] = {UNPACK2(mval)};
  SCULPT_cursor_geometry_info_update(C, &sgi, mval_fl, false);
  BKE_sculpt_update_object_for_edit(depsgraph, ob, true, false, false);

  /* Average the edge length of the connected edges to the active vertex. */
  int active_vertex = SCULPT_active_vertex_get(ss);
  const float *active_vertex_co = SCULPT_active_vertex_co_get(ss);
  float edge_length = 0.0f;
  int tot = 0;
  SculptVertexNeighborIter ni;
  SCULPT_VERTEX_NEIGHBORS_ITER_BEGIN (ss, active_vertex, ni) {
    edge_length += len_v3v3(active_vertex_co, SCULPT_vertex_co_get(ss, ni.index));
    tot += 1;
  }
  SCULPT_VERTEX_NEIGHBORS_ITER_END(ni);
  if (tot > 0) {
    mesh->remesh_voxel_size = edge_length / (float)tot;
  }
}

static void sculpt_raycast_detail_cb(PBVHNode *node, void *data_v, float *tmin)
{
  if (BKE_pbvh_node_get_tmin(node) < *tmin) {
    SculptDetailRaycastData *srd = data_v;
    if (BKE_pbvh_bmesh_node_raycast_detail(
            node, srd->ray_start, &srd->isect_precalc, &srd->depth, &srd->edge_length)) {
      srd->hit = true;
      *tmin = srd->depth;
    }
  }
}

static void sample_detail_dyntopo(bContext *C, ViewContext *vc, const int mval[2])
{
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;
  Object *ob = vc->obact;
  Brush *brush = BKE_paint_brush(&sd->paint);

  SCULPT_stroke_modifiers_check(C, ob, brush);

  const float mval_fl[2] = {UNPACK2(mval)};
  float ray_start[3], ray_end[3], ray_normal[3];
  float depth = SCULPT_raycast_init(vc, mval_fl, ray_start, ray_end, ray_normal, false);

  SculptDetailRaycastData srd;
  srd.hit = 0;
  srd.ray_start = ray_start;
  srd.depth = depth;
  srd.edge_length = 0.0f;
  isect_ray_tri_watertight_v3_precalc(&srd.isect_precalc, ray_normal);

  BKE_pbvh_raycast(ob->sculpt->pbvh, sculpt_raycast_detail_cb, &srd, ray_start, ray_normal, false);

  if (srd.hit && srd.edge_length > 0.0f) {
    /* Convert edge length to world space detail resolution. */
    sd->constant_detail = 1 / (srd.edge_length * mat4_to_scale(ob->obmat));
  }
}

static int sample_detail(bContext *C, const int event_xy[2], int mode)
{
  /* Find 3D view to pick from. */
  bScreen *screen = CTX_wm_screen(C);
  ScrArea *area = BKE_screen_find_area_xy(screen, SPACE_VIEW3D, event_xy);
  ARegion *region = (area) ? BKE_area_find_region_xy(area, RGN_TYPE_WINDOW, event_xy) : NULL;
  if (region == NULL) {
    return OPERATOR_CANCELLED;
  }

  /* Set context to 3D view. */
  ScrArea *prev_area = CTX_wm_area(C);
  ARegion *prev_region = CTX_wm_region(C);
  CTX_wm_area_set(C, area);
  CTX_wm_region_set(C, region);

  Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
  ViewContext vc;
  ED_view3d_viewcontext_init(C, &vc, depsgraph);

  Object *ob = vc.obact;
  if (ob == NULL) {
    return OPERATOR_CANCELLED;
  }

  SculptSession *ss = ob->sculpt;
  if (!ss->pbvh) {
    return OPERATOR_CANCELLED;
  }

  const int mval[2] = {
      event_xy[0] - region->winrct.xmin,
      event_xy[1] - region->winrct.ymin,
  };

  /* Pick sample detail. */
  switch (mode) {
    case SAMPLE_DETAIL_DYNTOPO:
      if (BKE_pbvh_type(ss->pbvh) != PBVH_BMESH) {
        CTX_wm_area_set(C, prev_area);
        CTX_wm_region_set(C, prev_region);
        return OPERATOR_CANCELLED;
      }
      sample_detail_dyntopo(C, &vc, mval);
      break;
    case SAMPLE_DETAIL_VOXEL:
      if (BKE_pbvh_type(ss->pbvh) != PBVH_FACES) {
        CTX_wm_area_set(C, prev_area);
        CTX_wm_region_set(C, prev_region);
        return OPERATOR_CANCELLED;
      }
      sample_detail_voxel(C, &vc, mval);
      break;
  }

  /* Restore context. */
  CTX_wm_area_set(C, prev_area);
  CTX_wm_region_set(C, prev_region);

  return OPERATOR_FINISHED;
}

static int sculpt_sample_detail_size_exec(bContext *C, wmOperator *op)
{
  int ss_co[2];
  RNA_int_get_array(op->ptr, "location", ss_co);
  int mode = RNA_enum_get(op->ptr, "mode");
  return sample_detail(C, ss_co, mode);
}

static int sculpt_sample_detail_size_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(e))
{
  ED_workspace_status_text(C, TIP_("Click on the mesh to set the detail"));
  WM_cursor_modal_set(CTX_wm_window(C), WM_CURSOR_EYEDROPPER);
  WM_event_add_modal_handler(C, op);
  return OPERATOR_RUNNING_MODAL;
}

static int sculpt_sample_detail_size_modal(bContext *C, wmOperator *op, const wmEvent *event)
{
  switch (event->type) {
    case LEFTMOUSE:
      if (event->val == KM_PRESS) {
        int mode = RNA_enum_get(op->ptr, "mode");
        sample_detail(C, event->xy, mode);

        RNA_int_set_array(op->ptr, "location", event->xy);
        WM_cursor_modal_restore(CTX_wm_window(C));
        ED_workspace_status_text(C, NULL);
        WM_main_add_notifier(NC_SCENE | ND_TOOLSETTINGS, NULL);

        return OPERATOR_FINISHED;
      }
      break;
    case EVT_ESCKEY:
    case RIGHTMOUSE: {
      WM_cursor_modal_restore(CTX_wm_window(C));
      ED_workspace_status_text(C, NULL);

      return OPERATOR_CANCELLED;
    }
  }

  return OPERATOR_RUNNING_MODAL;
}

void SCULPT_OT_sample_detail_size(wmOperatorType *ot)
{
  /* Identifiers. */
  ot->name = "Sample Detail Size";
  ot->idname = "SCULPT_OT_sample_detail_size";
  ot->description = "Sample the mesh detail on clicked point";

  /* API callbacks. */
  ot->invoke = sculpt_sample_detail_size_invoke;
  ot->exec = sculpt_sample_detail_size_exec;
  ot->modal = sculpt_sample_detail_size_modal;
  ot->poll = SCULPT_mode_poll;

  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;

  RNA_def_int_array(ot->srna,
                    "location",
                    2,
                    NULL,
                    0,
                    SHRT_MAX,
                    "Location",
                    "Screen coordinates of sampling",
                    0,
                    SHRT_MAX);
  RNA_def_enum(ot->srna,
               "mode",
               prop_sculpt_sample_detail_mode_types,
               SAMPLE_DETAIL_DYNTOPO,
               "Detail Mode",
               "Target sculpting workflow that is going to use the sampled size");
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Dynamic-topology detail size
 *
 * Currently, there are two operators editing the detail size:
 * - #SCULPT_OT_set_detail_size uses radial control for all methods
 * - #SCULPT_OT_dyntopo_detail_size_edit shows a triangle grid representation of the detail
 *   resolution (for constant detail method,
 *   falls back to radial control for the remaining methods).
 * \{ */

static void set_brush_rc_props(PointerRNA *ptr, const char *prop)
{
  char *path = BLI_sprintfN("tool_settings.sculpt.brush.%s", prop);
  RNA_string_set(ptr, "data_path_primary", path);
  MEM_freeN(path);
}

static void sculpt_detail_size_set_radial_control(bContext *C)
{
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;

  PointerRNA props_ptr;
  wmOperatorType *ot = WM_operatortype_find("WM_OT_radial_control", true);

  WM_operator_properties_create_ptr(&props_ptr, ot);

  if (sd->flags & (SCULPT_DYNTOPO_DETAIL_CONSTANT | SCULPT_DYNTOPO_DETAIL_MANUAL)) {
    set_brush_rc_props(&props_ptr, "constant_detail_resolution");
    RNA_string_set(
        &props_ptr, "data_path_primary", "tool_settings.sculpt.constant_detail_resolution");
  }
  else if (sd->flags & SCULPT_DYNTOPO_DETAIL_BRUSH) {
    set_brush_rc_props(&props_ptr, "constant_detail_resolution");
    RNA_string_set(&props_ptr, "data_path_primary", "tool_settings.sculpt.detail_percent");
  }
  else {
    set_brush_rc_props(&props_ptr, "detail_size");
    RNA_string_set(&props_ptr, "data_path_primary", "tool_settings.sculpt.detail_size");
  }

  WM_operator_name_call_ptr(C, ot, WM_OP_INVOKE_DEFAULT, &props_ptr, NULL);

  WM_operator_properties_free(&props_ptr);
}

static int sculpt_set_detail_size_exec(bContext *C, wmOperator *UNUSED(op))
{
  sculpt_detail_size_set_radial_control(C);

  return OPERATOR_FINISHED;
}

void SCULPT_OT_set_detail_size(wmOperatorType *ot)
{
  /* Identifiers. */
  ot->name = "Set Detail Size";
  ot->idname = "SCULPT_OT_set_detail_size";
  ot->description =
      "Set the mesh detail (either relative or constant one, depending on current dyntopo mode)";

  /* API callbacks. */
  ot->exec = sculpt_set_detail_size_exec;
  ot->poll = sculpt_and_dynamic_topology_poll;

  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Dyntopo Detail Size Edit Operator
 * \{ */

/* Defines how much the mouse movement will modify the detail size value. */
#define DETAIL_SIZE_DELTA_SPEED 0.08f
#define DETAIL_SIZE_DELTA_ACCURATE_SPEED 0.004f

typedef struct DyntopoDetailSizeEditCustomData {
  void *draw_handle;
  Object *active_object;

  float init_mval[2];
  float accurate_mval[2];

  float outline_col[4];

  bool accurate_mode;
  bool sample_mode;

  float init_detail_size;
  float accurate_detail_size;
  float detail_size;
  float radius;

  float preview_tri[3][3];
  float gizmo_mat[4][4];
} DyntopoDetailSizeEditCustomData;

static void dyntopo_detail_size_parallel_lines_draw(uint pos3d,
                                                    DyntopoDetailSizeEditCustomData *cd,
                                                    const float start_co[3],
                                                    const float end_co[3],
                                                    bool flip,
                                                    const float angle)
{
  float object_space_constant_detail = 1.0f /
                                       (cd->detail_size * mat4_to_scale(cd->active_object->obmat));

  /* The constant detail represents the maximum edge length allowed before subdividing it. If the
   * triangle grid preview is created with this value it will represent an ideal mesh density where
   * all edges have the exact maximum length, which never happens in practice. As the minimum edge
   * length for dyntopo is 0.4 * max_edge_length, this adjust the detail size to the average
   * between max and min edge length so the preview is more accurate. */
  object_space_constant_detail *= 0.7f;

  const float total_len = len_v3v3(cd->preview_tri[0], cd->preview_tri[1]);
  const int tot_lines = (int)(total_len / object_space_constant_detail) + 1;
  const float tot_lines_fl = total_len / object_space_constant_detail;
  float spacing_disp[3];
  sub_v3_v3v3(spacing_disp, end_co, start_co);
  normalize_v3(spacing_disp);

  float line_disp[3];
  rotate_v2_v2fl(line_disp, spacing_disp, DEG2RAD(angle));
  mul_v3_fl(spacing_disp, total_len / tot_lines_fl);

  immBegin(GPU_PRIM_LINES, (uint)tot_lines * 2);
  for (int i = 0; i < tot_lines; i++) {
    float line_length;
    if (flip) {
      line_length = total_len * ((float)i / (float)tot_lines_fl);
    }
    else {
      line_length = total_len * (1.0f - ((float)i / (float)tot_lines_fl));
    }
    float line_start[3];
    copy_v3_v3(line_start, start_co);
    madd_v3_v3v3fl(line_start, line_start, spacing_disp, i);
    float line_end[3];
    madd_v3_v3v3fl(line_end, line_start, line_disp, line_length);
    immVertex3fv(pos3d, line_start);
    immVertex3fv(pos3d, line_end);
  }
  immEnd();
}

static void dyntopo_detail_size_edit_draw(const bContext *UNUSED(C),
                                          ARegion *UNUSED(ar),
                                          void *arg)
{
  DyntopoDetailSizeEditCustomData *cd = arg;
  GPU_blend(GPU_BLEND_ALPHA);
  GPU_line_smooth(true);

  uint pos3d = GPU_vertformat_attr_add(immVertexFormat(), "pos", GPU_COMP_F32, 3, GPU_FETCH_FLOAT);
  immBindBuiltinProgram(GPU_SHADER_3D_UNIFORM_COLOR);
  GPU_matrix_push();
  GPU_matrix_mul(cd->gizmo_mat);

  /* Draw Cursor */
  immUniformColor4fv(cd->outline_col);
  GPU_line_width(3.0f);

  imm_draw_circle_wire_3d(pos3d, 0, 0, cd->radius, 80);

  /* Draw Triangle. */
  immUniformColor4f(0.9f, 0.9f, 0.9f, 0.8f);
  immBegin(GPU_PRIM_LINES, 6);
  immVertex3fv(pos3d, cd->preview_tri[0]);
  immVertex3fv(pos3d, cd->preview_tri[1]);

  immVertex3fv(pos3d, cd->preview_tri[1]);
  immVertex3fv(pos3d, cd->preview_tri[2]);

  immVertex3fv(pos3d, cd->preview_tri[2]);
  immVertex3fv(pos3d, cd->preview_tri[0]);
  immEnd();

  /* Draw Grid */
  GPU_line_width(1.0f);
  dyntopo_detail_size_parallel_lines_draw(
      pos3d, cd, cd->preview_tri[0], cd->preview_tri[1], false, 60.0f);
  dyntopo_detail_size_parallel_lines_draw(
      pos3d, cd, cd->preview_tri[0], cd->preview_tri[1], true, 120.0f);
  dyntopo_detail_size_parallel_lines_draw(
      pos3d, cd, cd->preview_tri[0], cd->preview_tri[2], false, -60.0f);

  immUnbindProgram();
  GPU_matrix_pop();
  GPU_blend(GPU_BLEND_NONE);
  GPU_line_smooth(false);
}

static void dyntopo_detail_size_edit_cancel(bContext *C, wmOperator *op)
{
  Object *active_object = CTX_data_active_object(C);
  SculptSession *ss = active_object->sculpt;
  ARegion *region = CTX_wm_region(C);
  DyntopoDetailSizeEditCustomData *cd = op->customdata;
  ED_region_draw_cb_exit(region->type, cd->draw_handle);
  ss->draw_faded_cursor = false;
  MEM_freeN(op->customdata);
  ED_workspace_status_text(C, NULL);
}

static void dyntopo_detail_size_sample_from_surface(Object *ob,
                                                    DyntopoDetailSizeEditCustomData *cd)
{
  SculptSession *ss = ob->sculpt;
  const int active_vertex = SCULPT_active_vertex_get(ss);

  float len_accum = 0;
  int num_neighbors = 0;
  SculptVertexNeighborIter ni;
  SCULPT_VERTEX_NEIGHBORS_ITER_BEGIN (ss, active_vertex, ni) {
    len_accum += len_v3v3(SCULPT_vertex_co_get(ss, active_vertex),
                          SCULPT_vertex_co_get(ss, ni.index));
    num_neighbors++;
  }
  SCULPT_VERTEX_NEIGHBORS_ITER_END(ni);

  if (num_neighbors > 0) {
    const float avg_edge_len = len_accum / num_neighbors;
    /* Use 0.7 as the average of min and max dyntopo edge length. */
    const float detail_size = 0.7f / (avg_edge_len * mat4_to_scale(cd->active_object->obmat));
    cd->detail_size = clamp_f(detail_size, 1.0f, 500.0f);
  }
}

static void dyntopo_detail_size_update_from_mouse_delta(DyntopoDetailSizeEditCustomData *cd,
                                                        const wmEvent *event)
{
  const float mval[2] = {event->mval[0], event->mval[1]};

  float detail_size_delta;
  if (cd->accurate_mode) {
    detail_size_delta = mval[0] - cd->accurate_mval[0];
    cd->detail_size = cd->accurate_detail_size +
                      detail_size_delta * DETAIL_SIZE_DELTA_ACCURATE_SPEED;
  }
  else {
    detail_size_delta = mval[0] - cd->init_mval[0];
    cd->detail_size = cd->init_detail_size + detail_size_delta * DETAIL_SIZE_DELTA_SPEED;
  }

  if (event->type == EVT_LEFTSHIFTKEY && event->val == KM_PRESS) {
    cd->accurate_mode = true;
    copy_v2_v2(cd->accurate_mval, mval);
    cd->accurate_detail_size = cd->detail_size;
  }
  if (event->type == EVT_LEFTSHIFTKEY && event->val == KM_RELEASE) {
    cd->accurate_mode = false;
    cd->accurate_detail_size = 0.0f;
  }

  cd->detail_size = clamp_f(cd->detail_size, 1.0f, 500.0f);
}

static int dyntopo_detail_size_edit_modal(bContext *C, wmOperator *op, const wmEvent *event)
{
  Object *active_object = CTX_data_active_object(C);
  SculptSession *ss = active_object->sculpt;
  ARegion *region = CTX_wm_region(C);
  DyntopoDetailSizeEditCustomData *cd = op->customdata;
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;

  /* Cancel modal operator */
  if ((event->type == EVT_ESCKEY && event->val == KM_PRESS) ||
      (event->type == RIGHTMOUSE && event->val == KM_PRESS)) {
    dyntopo_detail_size_edit_cancel(C, op);
    ED_region_tag_redraw(region);
    return OPERATOR_FINISHED;
  }

  /* Finish modal operator */
  if ((event->type == LEFTMOUSE && event->val == KM_RELEASE) ||
      (event->type == EVT_RETKEY && event->val == KM_PRESS) ||
      (event->type == EVT_PADENTER && event->val == KM_PRESS)) {
    ED_region_draw_cb_exit(region->type, cd->draw_handle);
    sd->constant_detail = cd->detail_size;
    ss->draw_faded_cursor = false;
    MEM_freeN(op->customdata);
    ED_region_tag_redraw(region);
    ED_workspace_status_text(C, NULL);
    return OPERATOR_FINISHED;
  }

  ED_region_tag_redraw(region);

  if (ELEM(event->type, EVT_LEFTCTRLKEY, EVT_RIGHTCTRLKEY)) {
    if (event->val == KM_PRESS) {
      cd->sample_mode = true;
    }
    else if (event->val == KM_RELEASE) {
      cd->sample_mode = false;
    }
  }

  /* Sample mode sets the detail size sampling the average edge length under the surface. */
  if (cd->sample_mode) {
    dyntopo_detail_size_sample_from_surface(active_object, cd);
    return OPERATOR_RUNNING_MODAL;
  }
  /* Regular mode, changes the detail size by moving the cursor. */
  dyntopo_detail_size_update_from_mouse_delta(cd, event);

  return OPERATOR_RUNNING_MODAL;
}

static int dyntopo_detail_size_edit_invoke(bContext *C, wmOperator *op, const wmEvent *event)
{
  Sculpt *sd = CTX_data_tool_settings(C)->sculpt;

  /* Fallback to radial control for modes other than SCULPT_DYNTOPO_DETAIL_CONSTANT [same as in
   * SCULPT_OT_set_detail_size]. */
  if (!(sd->flags & (SCULPT_DYNTOPO_DETAIL_CONSTANT | SCULPT_DYNTOPO_DETAIL_MANUAL))) {
    sculpt_detail_size_set_radial_control(C);

    return OPERATOR_FINISHED;
  }

  /* Special method for SCULPT_DYNTOPO_DETAIL_CONSTANT. */
  ARegion *region = CTX_wm_region(C);
  Object *active_object = CTX_data_active_object(C);
  Brush *brush = BKE_paint_brush(&sd->paint);

  DyntopoDetailSizeEditCustomData *cd = MEM_callocN(sizeof(DyntopoDetailSizeEditCustomData),
                                                    "Dyntopo Detail Size Edit OP Custom Data");

  /* Initial operator Custom Data setup. */
  cd->draw_handle = ED_region_draw_cb_activate(
      region->type, dyntopo_detail_size_edit_draw, cd, REGION_DRAW_POST_VIEW);
  cd->active_object = active_object;
  cd->init_mval[0] = event->mval[0];
  cd->init_mval[1] = event->mval[1];
  cd->detail_size = sd->constant_detail;
  cd->init_detail_size = sd->constant_detail;
  copy_v4_v4(cd->outline_col, brush->add_col);
  op->customdata = cd;

  SculptSession *ss = active_object->sculpt;
  cd->radius = ss->cursor_radius;

  /* Generates the matrix to position the gizmo in the surface of the mesh using the same location
   * and orientation as the brush cursor. */
  float cursor_trans[4][4], cursor_rot[4][4];
  const float z_axis[4] = {0.0f, 0.0f, 1.0f, 0.0f};
  float quat[4];
  copy_m4_m4(cursor_trans, active_object->obmat);
  translate_m4(
      cursor_trans, ss->cursor_location[0], ss->cursor_location[1], ss->cursor_location[2]);

  float cursor_normal[3];
  if (!is_zero_v3(ss->cursor_sampled_normal)) {
    copy_v3_v3(cursor_normal, ss->cursor_sampled_normal);
  }
  else {
    copy_v3_v3(cursor_normal, ss->cursor_normal);
  }

  rotation_between_vecs_to_quat(quat, z_axis, cursor_normal);
  quat_to_mat4(cursor_rot, quat);
  copy_m4_m4(cd->gizmo_mat, cursor_trans);
  mul_m4_m4_post(cd->gizmo_mat, cursor_rot);

  /* Initialize the position of the triangle vertices. */
  const float y_axis[3] = {0.0f, cd->radius, 0.0f};
  for (int i = 0; i < 3; i++) {
    zero_v3(cd->preview_tri[i]);
    rotate_v2_v2fl(cd->preview_tri[i], y_axis, DEG2RAD(120.0f * i));
  }

  SCULPT_vertex_random_access_ensure(ss);

  WM_event_add_modal_handler(C, op);
  ED_region_tag_redraw(region);

  ss->draw_faded_cursor = true;

  const char *status_str = TIP_(
      "Move the mouse to change the dyntopo detail size. LMB: confirm size, ESC/RMB: cancel");
  ED_workspace_status_text(C, status_str);

  return OPERATOR_RUNNING_MODAL;
}

void SCULPT_OT_dyntopo_detail_size_edit(wmOperatorType *ot)
{
  /* identifiers */
  ot->name = "Edit Dyntopo Detail Size";
  ot->description = "Modify the detail size of dyntopo interactively";
  ot->idname = "SCULPT_OT_dyntopo_detail_size_edit";

  /* api callbacks */
  ot->poll = sculpt_and_dynamic_topology_poll;
  ot->invoke = dyntopo_detail_size_edit_invoke;
  ot->modal = dyntopo_detail_size_edit_modal;
  ot->cancel = dyntopo_detail_size_edit_cancel;

  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
}

/** \} */