GPencil: Refactor of Draw Engine, Vertex Paint and all internal functions

This commit is a full refactor of the grease pencil modules including Draw Engine, Modifiers, VFX, depsgraph update, improvements in operators and conversion of Sculpt and Weight paint tools to real brushes.

Also, a huge code cleanup has been done at all levels.

Thanks to @fclem for his work and yo @pepeland and @mendio for the testing and help in the development.

Differential Revision: https://developer.blender.org/D6293

1 files changed, 901 insertions, 0 deletions

diff --git a/source/blender/editors/gpencil/gpencil_weight_paint.c b/source/blender/editors/gpencil/gpencil_weight_paint.c
new file mode 100644
index 00000000000..6b337afa559
--- /dev/null
+++ b/source/blender/editors/gpencil/gpencil_weight_paint.c
@@ -0,0 +1,901 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2015, Blender Foundation
+ * This is a new part of Blender
+ * Brush based operators for editing Grease Pencil strokes
+ */
+
+/** \file
+ * \ingroup edgpencil
+ */
+
+#include "MEM_guardedalloc.h"
+
+#include "BLI_blenlib.h"
+#include "BLI_math.h"
+
+#include "BLT_translation.h"
+
+#include "DNA_brush_types.h"
+#include "DNA_gpencil_types.h"
+
+#include "BKE_brush.h"
+#include "BKE_colortools.h"
+#include "BKE_context.h"
+#include "BKE_deform.h"
+#include "BKE_gpencil.h"
+#include "BKE_main.h"
+#include "DNA_meshdata_types.h"
+#include "BKE_object_deform.h"
+#include "BKE_report.h"
+
+#include "WM_api.h"
+#include "WM_types.h"
+
+#include "RNA_access.h"
+#include "RNA_define.h"
+
+#include "UI_view2d.h"
+
+#include "ED_gpencil.h"
+#include "ED_screen.h"
+#include "ED_view3d.h"
+
+#include "DEG_depsgraph.h"
+#include "DEG_depsgraph_query.h"
+
+#include "gpencil_intern.h"
+
+/* ************************************************ */
+/* General Brush Editing Context */
+#define GP_SELECT_BUFFER_CHUNK 256
+
+/* Grid of Colors for Smear. */
+typedef struct tGP_Grid {
+  /** Lower right corner of rectangle of grid cell. */
+  float bottom[2];
+  /** Upper left corner of rectangle of grid cell. */
+  float top[2];
+  /** Average Color */
+  float color[4];
+  /** Total points included. */
+  int totcol;
+
+} tGP_Grid;
+
+/* List of points affected by brush. */
+typedef struct tGP_Selected {
+  /** Referenced stroke. */
+  bGPDstroke *gps;
+  /** Point index in points array. */
+  int pt_index;
+  /** Position */
+  int pc[2];
+  /** Color */
+  float color[4];
+} tGP_Selected;
+
+/* Context for brush operators */
+typedef struct tGP_BrushWeightpaintData {
+  struct Main *bmain;
+  Scene *scene;
+  Object *object;
+
+  ARegion *region;
+
+  /* Current GPencil datablock */
+  bGPdata *gpd;
+
+  Brush *brush;
+
+  /* Space Conversion Data */
+  GP_SpaceConversion gsc;
+
+  /* Is the brush currently painting? */
+  bool is_painting;
+
+  /* Start of new paint */
+  bool first;
+
+  /* Is multiframe editing enabled, and are we using falloff for that? */
+  bool is_multiframe;
+  bool use_multiframe_falloff;
+
+  /* active vertex group */
+  int vrgroup;
+
+  /* Brush Runtime Data: */
+  /* - position and pressure
+   * - the *_prev variants are the previous values
+   */
+  float mval[2], mval_prev[2];
+  float pressure, pressure_prev;
+
+  /* - Effect 2D vector */
+  float dvec[2];
+
+  /* - multiframe falloff factor */
+  float mf_falloff;
+
+  /* brush geometry (bounding box) */
+  rcti brush_rect;
+
+  /* Temp data to save selected points */
+  /** Stroke buffer. */
+  tGP_Selected *pbuffer;
+  /** Number of elements currently used in cache. */
+  int pbuffer_used;
+  /** Number of total elements available in cache. */
+  int pbuffer_size;
+} tGP_BrushWeightpaintData;
+
+/* Ensure the buffer to hold temp selected point size is enough to save all points selected. */
+static tGP_Selected *gpencil_select_buffer_ensure(tGP_Selected *buffer_array,
+                                                  int *buffer_size,
+                                                  int *buffer_used,
+                                                  const bool clear)
+{
+  tGP_Selected *p = NULL;
+
+  /* By default a buffer is created with one block with a predefined number of free slots,
+   * if the size is not enough, the cache is reallocated adding a new block of free slots.
+   * This is done in order to keep cache small and improve speed. */
+  if (*buffer_used + 1 > *buffer_size) {
+    if ((*buffer_size == 0) || (buffer_array == NULL)) {
+      p = MEM_callocN(sizeof(struct tGP_Selected) * GP_SELECT_BUFFER_CHUNK, __func__);
+      *buffer_size = GP_SELECT_BUFFER_CHUNK;
+    }
+    else {
+      *buffer_size += GP_SELECT_BUFFER_CHUNK;
+      p = MEM_recallocN(buffer_array, sizeof(struct tGP_Selected) * *buffer_size);
+    }
+
+    if (p == NULL) {
+      *buffer_size = *buffer_used = 0;
+    }
+
+    buffer_array = p;
+  }
+
+  /* clear old data */
+  if (clear) {
+    *buffer_used = 0;
+    if (buffer_array != NULL) {
+      memset(buffer_array, 0, sizeof(tGP_Selected) * *buffer_size);
+    }
+  }
+
+  return buffer_array;
+}
+
+/* Brush Operations ------------------------------- */
+
+/* Compute strength of effect. */
+static float brush_influence_calc(tGP_BrushWeightpaintData *gso, const int radius, const int co[2])
+{
+  Brush *brush = gso->brush;
+
+  /* basic strength factor from brush settings */
+  float influence = brush->alpha;
+
+  /* use pressure? */
+  if (brush->gpencil_settings->flag & GP_BRUSH_USE_PRESSURE) {
+    influence *= gso->pressure;
+  }
+
+  /* distance fading */
+  int mval_i[2];
+  round_v2i_v2fl(mval_i, gso->mval);
+  float distance = (float)len_v2v2_int(mval_i, co);
+  influence *= 1.0f - (distance / max_ff(radius, 1e-8));
+
+  /* Apply Brush curve. */
+  float brush_fallof = BKE_brush_curve_strength(brush, distance, (float)radius);
+  influence *= brush_fallof;
+
+  /* apply multiframe falloff */
+  influence *= gso->mf_falloff;
+
+  /* return influence */
+  return influence;
+}
+
+/* Compute effect vector for directional brushes. */
+static void brush_calc_dvec_2d(tGP_BrushWeightpaintData *gso)
+{
+  gso->dvec[0] = (float)(gso->mval[0] - gso->mval_prev[0]);
+  gso->dvec[1] = (float)(gso->mval[1] - gso->mval_prev[1]);
+
+  normalize_v2(gso->dvec);
+}
+
+/* ************************************************ */
+/* Brush Callbacks
+ * This section defines the callbacks used by each brush to perform their magic.
+ * These are called on each point within the brush's radius. */
+
+/* Draw Brush */
+static bool brush_draw_apply(tGP_BrushWeightpaintData *gso,
+                             bGPDstroke *gps,
+                             int pt_index,
+                             const int radius,
+                             const int co[2])
+{
+  /* create dvert */
+  BKE_gpencil_dvert_ensure(gps);
+
+  MDeformVert *dvert = gps->dvert + pt_index;
+  float inf;
+
+  /* Compute strength of effect */
+  inf = brush_influence_calc(gso, radius, co);
+
+  /* need a vertex group */
+  if (gso->vrgroup == -1) {
+    if (gso->object) {
+      BKE_object_defgroup_add(gso->object);
+      DEG_relations_tag_update(gso->bmain);
+      gso->vrgroup = 0;
+    }
+  }
+  else {
+    bDeformGroup *defgroup = BLI_findlink(&gso->object->defbase, gso->vrgroup);
+    if (defgroup->flag & DG_LOCK_WEIGHT) {
+      return false;
+    }
+  }
+  /* Get current weight and blend. */
+  MDeformWeight *dw = BKE_defvert_ensure_index(dvert, gso->vrgroup);
+  if (dw) {
+    dw->weight = interpf(gso->brush->weight, dw->weight, inf);
+    CLAMP(dw->weight, 0.0f, 1.0f);
+  }
+  return true;
+}
+
+/* ************************************************ */
+/* Header Info */
+static void gp_weightpaint_brush_header_set(bContext *C)
+{
+  ED_workspace_status_text(C, TIP_("GPencil Weight Paint: LMB to paint | RMB/Escape to Exit"));
+}
+
+/* ************************************************ */
+/* Grease Pencil Weight Paint Operator */
+
+/* Init/Exit ----------------------------------------------- */
+
+static bool gp_weightpaint_brush_init(bContext *C, wmOperator *op)
+{
+  Scene *scene = CTX_data_scene(C);
+  ToolSettings *ts = CTX_data_tool_settings(C);
+  Object *ob = CTX_data_active_object(C);
+  Paint *paint = &ts->gp_weightpaint->paint;
+
+  /* set the brush using the tool */
+  tGP_BrushWeightpaintData *gso;
+
+  /* setup operator data */
+  gso = MEM_callocN(sizeof(tGP_BrushWeightpaintData), "tGP_BrushWeightpaintData");
+  op->customdata = gso;
+
+  gso->bmain = CTX_data_main(C);
+
+  gso->brush = paint->brush;
+  BKE_curvemapping_initialize(gso->brush->curve);
+
+  gso->is_painting = false;
+  gso->first = true;
+
+  gso->pbuffer = NULL;
+  gso->pbuffer_size = 0;
+  gso->pbuffer_used = 0;
+
+  gso->gpd = ED_gpencil_data_get_active(C);
+  gso->scene = scene;
+  gso->object = ob;
+  if (ob) {
+    gso->vrgroup = ob->actdef - 1;
+    if (!BLI_findlink(&ob->defbase, gso->vrgroup)) {
+      gso->vrgroup = -1;
+    }
+  }
+  else {
+    gso->vrgroup = -1;
+  }
+
+  gso->region = CTX_wm_region(C);
+
+  /* Multiframe settings. */
+  gso->is_multiframe = (bool)GPENCIL_MULTIEDIT_SESSIONS_ON(gso->gpd);
+  gso->use_multiframe_falloff = (ts->gp_sculpt.flag & GP_SCULPT_SETT_FLAG_FRAME_FALLOFF) != 0;
+
+  /* Init multi-edit falloff curve data before doing anything,
+   * so we won't have to do it again later. */
+  if (gso->is_multiframe) {
+    BKE_curvemapping_initialize(ts->gp_sculpt.cur_falloff);
+  }
+
+  /* Setup space conversions. */
+  gp_point_conversion_init(C, &gso->gsc);
+
+  /* Update header. */
+  gp_weightpaint_brush_header_set(C);
+
+  return true;
+}
+
+static void gp_weightpaint_brush_exit(bContext *C, wmOperator *op)
+{
+  tGP_BrushWeightpaintData *gso = op->customdata;
+
+  /* Disable headerprints. */
+  ED_workspace_status_text(C, NULL);
+
+  /* Free operator data */
+  MEM_SAFE_FREE(gso->pbuffer);
+  MEM_SAFE_FREE(gso);
+  op->customdata = NULL;
+}
+
+/* Poll callback for stroke weight paint operator. */
+static bool gp_weightpaint_brush_poll(bContext *C)
+{
+  /* NOTE: this is a bit slower, but is the most accurate... */
+  return CTX_DATA_COUNT(C, editable_gpencil_strokes) != 0;
+}
+
+/* Helper to save the points selected by the brush. */
+static void gp_save_selected_point(tGP_BrushWeightpaintData *gso,
+                                   bGPDstroke *gps,
+                                   int index,
+                                   int pc[2])
+{
+  tGP_Selected *selected;
+  bGPDspoint *pt = &gps->points[index];
+
+  /* Ensure the array to save the list of selected points is big enough. */
+  gso->pbuffer = gpencil_select_buffer_ensure(
+      gso->pbuffer, &gso->pbuffer_size, &gso->pbuffer_used, false);
+
+  selected = &gso->pbuffer[gso->pbuffer_used];
+  selected->gps = gps;
+  selected->pt_index = index;
+  copy_v2_v2_int(selected->pc, pc);
+  copy_v4_v4(selected->color, pt->vert_color);
+
+  gso->pbuffer_used++;
+}
+
+/* Select points in this stroke and add to an array to be used later. */
+static void gp_weightpaint_select_stroke(tGP_BrushWeightpaintData *gso,
+                                         bGPDstroke *gps,
+                                         const float diff_mat[4][4])
+{
+  GP_SpaceConversion *gsc = &gso->gsc;
+  rcti *rect = &gso->brush_rect;
+  Brush *brush = gso->brush;
+  const int radius = (brush->flag & GP_BRUSH_USE_PRESSURE) ? gso->brush->size * gso->pressure :
+                                                             gso->brush->size;
+  bGPDstroke *gps_active = (gps->runtime.gps_orig) ? gps->runtime.gps_orig : gps;
+  bGPDspoint *pt_active = NULL;
+
+  bGPDspoint *pt1, *pt2;
+  bGPDspoint *pt = NULL;
+  int pc1[2] = {0};
+  int pc2[2] = {0};
+  int i;
+  int index;
+  bool include_last = false;
+
+  /* Check if the stroke collide with brush. */
+  if (!ED_gpencil_stroke_check_collision(gsc, gps, gso->mval, radius, diff_mat)) {
+    return;
+  }
+
+  if (gps->totpoints == 1) {
+    bGPDspoint pt_temp;
+    pt = &gps->points[0];
+    gp_point_to_parent_space(gps->points, diff_mat, &pt_temp);
+    gp_point_to_xy(gsc, gps, &pt_temp, &pc1[0], &pc1[1]);
+
+    pt_active = (pt->runtime.pt_orig) ? pt->runtime.pt_orig : pt;
+    /* do boundbox check first */
+    if ((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) {
+      /* only check if point is inside */
+      int mval_i[2];
+      round_v2i_v2fl(mval_i, gso->mval);
+      if (len_v2v2_int(mval_i, pc1) <= radius) {
+        /* apply operation to this point */
+        if (pt_active != NULL) {
+          gp_save_selected_point(gso, gps_active, 0, pc1);
+        }
+      }
+    }
+  }
+  else {
+    /* Loop over the points in the stroke, checking for intersections
+     * - an intersection means that we touched the stroke
+     */
+    for (i = 0; (i + 1) < gps->totpoints; i++) {
+      /* Get points to work with */
+      pt1 = gps->points + i;
+      pt2 = gps->points + i + 1;
+
+      bGPDspoint npt;
+      gp_point_to_parent_space(pt1, diff_mat, &npt);
+      gp_point_to_xy(gsc, gps, &npt, &pc1[0], &pc1[1]);
+
+      gp_point_to_parent_space(pt2, diff_mat, &npt);
+      gp_point_to_xy(gsc, gps, &npt, &pc2[0], &pc2[1]);
+
+      /* Check that point segment of the boundbox of the selection stroke */
+      if (((!ELEM(V2D_IS_CLIPPED, pc1[0], pc1[1])) && BLI_rcti_isect_pt(rect, pc1[0], pc1[1])) ||
+          ((!ELEM(V2D_IS_CLIPPED, pc2[0], pc2[1])) && BLI_rcti_isect_pt(rect, pc2[0], pc2[1]))) {
+        /* Check if point segment of stroke had anything to do with
+         * brush region  (either within stroke painted, or on its lines)
+         * - this assumes that linewidth is irrelevant
+         */
+        if (gp_stroke_inside_circle(
+                gso->mval, gso->mval_prev, radius, pc1[0], pc1[1], pc2[0], pc2[1])) {
+
+          /* To each point individually... */
+          pt = &gps->points[i];
+          pt_active = (pt->runtime.pt_orig) ? pt->runtime.pt_orig : pt;
+          index = (pt->runtime.pt_orig) ? pt->runtime.idx_orig : i;
+          if (pt_active != NULL) {
+            gp_save_selected_point(gso, gps_active, index, pc1);
+          }
+
+          /* Only do the second point if this is the last segment,
+           * and it is unlikely that the point will get handled
+           * otherwise.
+           *
+           * NOTE: There is a small risk here that the second point wasn't really
+           *       actually in-range. In that case, it only got in because
+           *       the line linking the points was!
+           */
+          if (i + 1 == gps->totpoints - 1) {
+            pt = &gps->points[i + 1];
+            pt_active = (pt->runtime.pt_orig) ? pt->runtime.pt_orig : pt;
+            index = (pt->runtime.pt_orig) ? pt->runtime.idx_orig : i + 1;
+            if (pt_active != NULL) {
+              gp_save_selected_point(gso, gps_active, index, pc2);
+              include_last = false;
+            }
+          }
+          else {
+            include_last = true;
+          }
+        }
+        else if (include_last) {
+          /* This case is for cases where for whatever reason the second vert (1st here)
+           * doesn't get included because the whole edge isn't in bounds,
+           * but it would've qualified since it did with the previous step
+           * (but wasn't added then, to avoid double-ups).
+           */
+          pt = &gps->points[i];
+          pt_active = (pt->runtime.pt_orig) ? pt->runtime.pt_orig : pt;
+          index = (pt->runtime.pt_orig) ? pt->runtime.idx_orig : i;
+          if (pt_active != NULL) {
+            gp_save_selected_point(gso, gps_active, index, pc1);
+
+            include_last = false;
+          }
+        }
+      }
+    }
+  }
+}
+
+/* Apply weight paint brushes to strokes in the given frame. */
+static bool gp_weightpaint_brush_do_frame(bContext *C,
+                                          tGP_BrushWeightpaintData *gso,
+                                          bGPDlayer *gpl,
+                                          bGPDframe *gpf,
+                                          const float diff_mat[4][4])
+{
+  Object *ob = CTX_data_active_object(C);
+  char tool = gso->brush->gpencil_weight_tool;
+  const int radius = (gso->brush->flag & GP_BRUSH_USE_PRESSURE) ?
+                         gso->brush->size * gso->pressure :
+                         gso->brush->size;
+  tGP_Selected *selected = NULL;
+  int i;
+
+  /*---------------------------------------------------------------------
+   * First step: select the points affected. This step is required to have
+   * all selected points before apply the effect, because it could be
+   * required to do some step. Now is not used, but the operator is ready.
+   *--------------------------------------------------------------------- */
+  LISTBASE_FOREACH (bGPDstroke *, gps, &gpf->strokes) {
+    /* Skip strokes that are invalid for current view. */
+    if (ED_gpencil_stroke_can_use(C, gps) == false) {
+      continue;
+    }
+    /* Check if the color is editable. */
+    if (ED_gpencil_stroke_color_use(ob, gpl, gps) == false) {
+      continue;
+    }
+
+    /* Check points below the brush. */
+    gp_weightpaint_select_stroke(gso, gps, diff_mat);
+  }
+
+  /*---------------------------------------------------------------------
+   * Second step: Apply effect.
+   *--------------------------------------------------------------------- */
+  bool changed = false;
+  for (i = 0; i < gso->pbuffer_used; i++) {
+    changed = true;
+    selected = &gso->pbuffer[i];
+
+    switch (tool) {
+      case GPWEIGHT_TOOL_DRAW: {
+        brush_draw_apply(gso, selected->gps, selected->pt_index, radius, selected->pc);
+        changed |= true;
+        break;
+      }
+      default:
+        printf("ERROR: Unknown type of GPencil Weight Paint brush\n");
+        break;
+    }
+  }
+  /* Clear the selected array, but keep the memory allocation.*/
+  gso->pbuffer = gpencil_select_buffer_ensure(
+      gso->pbuffer, &gso->pbuffer_size, &gso->pbuffer_used, true);
+
+  return changed;
+}
+
+/* Apply brush effect to all layers. */
+static bool gp_weightpaint_brush_apply_to_layers(bContext *C, tGP_BrushWeightpaintData *gso)
+{
+  ToolSettings *ts = CTX_data_tool_settings(C);
+  Depsgraph *depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
+  Object *obact = gso->object;
+  bool changed = false;
+
+  Object *ob_eval = (Object *)DEG_get_evaluated_id(depsgraph, &obact->id);
+  bGPdata *gpd = (bGPdata *)ob_eval->data;
+
+  /* Find visible strokes, and perform operations on those if hit */
+  LISTBASE_FOREACH (bGPDlayer *, gpl, &gpd->layers) {
+    /* If locked or no active frame, don't do anything. */
+    if ((!BKE_gpencil_layer_is_editable(gpl)) || (gpl->actframe == NULL)) {
+      continue;
+    }
+
+    /* calculate difference matrix */
+    float diff_mat[4][4];
+    BKE_gpencil_parent_matrix_get(depsgraph, obact, gpl, diff_mat);
+
+    /* Active Frame or MultiFrame? */
+    if (gso->is_multiframe) {
+      /* init multiframe falloff options */
+      int f_init = 0;
+      int f_end = 0;
+
+      if (gso->use_multiframe_falloff) {
+        BKE_gpencil_frame_range_selected(gpl, &f_init, &f_end);
+      }
+
+      LISTBASE_FOREACH (bGPDframe *, gpf, &gpl->frames) {
+        /* Always do active frame; Otherwise, only include selected frames */
+        if ((gpf == gpl->actframe) || (gpf->flag & GP_FRAME_SELECT)) {
+          /* compute multiframe falloff factor */
+          if (gso->use_multiframe_falloff) {
+            /* Faloff depends on distance to active frame (relative to the overall frame range)
+             */
+            gso->mf_falloff = BKE_gpencil_multiframe_falloff_calc(
+                gpf, gpl->actframe->framenum, f_init, f_end, ts->gp_sculpt.cur_falloff);
+          }
+          else {
+            /* No falloff */
+            gso->mf_falloff = 1.0f;
+          }
+
+          /* affect strokes in this frame */
+          changed |= gp_weightpaint_brush_do_frame(C, gso, gpl, gpf, diff_mat);
+        }
+      }
+    }
+    else {
+      if (gpl->actframe != NULL) {
+        /* Apply to active frame's strokes */
+        gso->mf_falloff = 1.0f;
+        changed |= gp_weightpaint_brush_do_frame(C, gso, gpl, gpl->actframe, diff_mat);
+      }
+    }
+  }
+
+  return changed;
+}
+
+/* Calculate settings for applying brush */
+static void gp_weightpaint_brush_apply(bContext *C, wmOperator *op, PointerRNA *itemptr)
+{
+  tGP_BrushWeightpaintData *gso = op->customdata;
+  Brush *brush = gso->brush;
+  const int radius = ((brush->flag & GP_BRUSH_USE_PRESSURE) ? gso->brush->size * gso->pressure :
+                                                              gso->brush->size);
+  float mousef[2];
+  int mouse[2];
+  bool changed = false;
+
+  /* Get latest mouse coordinates */
+  RNA_float_get_array(itemptr, "mouse", mousef);
+  gso->mval[0] = mouse[0] = (int)(mousef[0]);
+  gso->mval[1] = mouse[1] = (int)(mousef[1]);
+
+  gso->pressure = RNA_float_get(itemptr, "pressure");
+
+  /* Store coordinates as reference, if operator just started running */
+  if (gso->first) {
+    gso->mval_prev[0] = gso->mval[0];
+    gso->mval_prev[1] = gso->mval[1];
+    gso->pressure_prev = gso->pressure;
+  }
+
+  /* Update brush_rect, so that it represents the bounding rectangle of brush. */
+  gso->brush_rect.xmin = mouse[0] - radius;
+  gso->brush_rect.ymin = mouse[1] - radius;
+  gso->brush_rect.xmax = mouse[0] + radius;
+  gso->brush_rect.ymax = mouse[1] + radius;
+
+  /* Calc 2D direction vector and relative angle. */
+  brush_calc_dvec_2d(gso);
+
+  changed = gp_weightpaint_brush_apply_to_layers(C, gso);
+
+  /* Updates */
+  if (changed) {
+    DEG_id_tag_update(&gso->gpd->id, ID_RECALC_GEOMETRY);
+    WM_event_add_notifier(C, NC_GPENCIL | ND_DATA | NA_EDITED, NULL);
+  }
+
+  /* Store values for next step */
+  gso->mval_prev[0] = gso->mval[0];
+  gso->mval_prev[1] = gso->mval[1];
+  gso->pressure_prev = gso->pressure;
+  gso->first = false;
+}
+
+/* Running --------------------------------------------- */
+
+/* helper - a record stroke, and apply paint event */
+static void gp_weightpaint_brush_apply_event(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  tGP_BrushWeightpaintData *gso = op->customdata;
+  PointerRNA itemptr;
+  float mouse[2];
+
+  mouse[0] = event->mval[0] + 1;
+  mouse[1] = event->mval[1] + 1;
+
+  /* fill in stroke */
+  RNA_collection_add(op->ptr, "stroke", &itemptr);
+
+  RNA_float_set_array(&itemptr, "mouse", mouse);
+  RNA_boolean_set(&itemptr, "pen_flip", event->ctrl != false);
+  RNA_boolean_set(&itemptr, "is_start", gso->first);
+
+  /* Handle pressure sensitivity (which is supplied by tablets). */
+  float pressure = event->tablet.pressure;
+  CLAMP(pressure, 0.0f, 1.0f);
+  RNA_float_set(&itemptr, "pressure", pressure);
+
+  /* apply */
+  gp_weightpaint_brush_apply(C, op, &itemptr);
+}
+
+/* reapply */
+static int gp_weightpaint_brush_exec(bContext *C, wmOperator *op)
+{
+  if (!gp_weightpaint_brush_init(C, op)) {
+    return OPERATOR_CANCELLED;
+  }
+
+  RNA_BEGIN (op->ptr, itemptr, "stroke") {
+    gp_weightpaint_brush_apply(C, op, &itemptr);
+  }
+  RNA_END;
+
+  gp_weightpaint_brush_exit(C, op);
+
+  return OPERATOR_FINISHED;
+}
+
+/* start modal painting */
+static int gp_weightpaint_brush_invoke(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  tGP_BrushWeightpaintData *gso = NULL;
+  const bool is_modal = RNA_boolean_get(op->ptr, "wait_for_input");
+  const bool is_playing = ED_screen_animation_playing(CTX_wm_manager(C)) != NULL;
+
+  /* the operator cannot work while play animation */
+  if (is_playing) {
+    BKE_report(op->reports, RPT_ERROR, "Cannot Paint while play animation");
+
+    return OPERATOR_CANCELLED;
+  }
+
+  /* init painting data */
+  if (!gp_weightpaint_brush_init(C, op)) {
+    return OPERATOR_CANCELLED;
+  }
+
+  gso = op->customdata;
+
+  /* register modal handler */
+  WM_event_add_modal_handler(C, op);
+
+  /* start drawing immediately? */
+  if (is_modal == false) {
+    ARegion *region = CTX_wm_region(C);
+
+    /* apply first dab... */
+    gso->is_painting = true;
+    gp_weightpaint_brush_apply_event(C, op, event);
+
+    /* redraw view with feedback */
+    ED_region_tag_redraw(region);
+  }
+
+  return OPERATOR_RUNNING_MODAL;
+}
+
+/* painting - handle events */
+static int gp_weightpaint_brush_modal(bContext *C, wmOperator *op, const wmEvent *event)
+{
+  tGP_BrushWeightpaintData *gso = op->customdata;
+  const bool is_modal = RNA_boolean_get(op->ptr, "wait_for_input");
+  bool redraw_region = false;
+  bool redraw_toolsettings = false;
+
+  /* The operator can be in 2 states: Painting and Idling */
+  if (gso->is_painting) {
+    /* Painting  */
+    switch (event->type) {
+      /* Mouse Move = Apply somewhere else */
+      case MOUSEMOVE:
+      case INBETWEEN_MOUSEMOVE:
+        /* apply brush effect at new position */
+        gp_weightpaint_brush_apply_event(C, op, event);
+
+        /* force redraw, so that the cursor will at least be valid */
+        redraw_region = true;
+        break;
+
+      /* Painting mbut release = Stop painting (back to idle) */
+      case LEFTMOUSE:
+        if (is_modal) {
+          /* go back to idling... */
+          gso->is_painting = false;
+        }
+        else {
+          /* end painting, since we're not modal */
+          gso->is_painting = false;
+
+          gp_weightpaint_brush_exit(C, op);
+          return OPERATOR_FINISHED;
+        }
+        break;
+
+      /* Abort painting if any of the usual things are tried */
+      case MIDDLEMOUSE:
+      case RIGHTMOUSE:
+      case ESCKEY:
+        gp_weightpaint_brush_exit(C, op);
+        return OPERATOR_FINISHED;
+    }
+  }
+  else {
+    /* Idling */
+    BLI_assert(is_modal == true);
+
+    switch (event->type) {
+      /* Painting mbut press = Start painting (switch to painting state) */
+      case LEFTMOUSE:
+        /* do initial "click" apply */
+        gso->is_painting = true;
+        gso->first = true;
+
+        gp_weightpaint_brush_apply_event(C, op, event);
+        break;
+
+      /* Exit modal operator, based on the "standard" ops */
+      case RIGHTMOUSE:
+      case ESCKEY:
+        gp_weightpaint_brush_exit(C, op);
+        return OPERATOR_FINISHED;
+
+      /* MMB is often used for view manipulations */
+      case MIDDLEMOUSE:
+        return OPERATOR_PASS_THROUGH;
+
+      /* Mouse movements should update the brush cursor - Just redraw the active region */
+      case MOUSEMOVE:
+      case INBETWEEN_MOUSEMOVE:
+        redraw_region = true;
+        break;
+
+      /* Change Frame - Allowed */
+      case LEFTARROWKEY:
+      case RIGHTARROWKEY:
+      case UPARROWKEY:
+      case DOWNARROWKEY:
+        return OPERATOR_PASS_THROUGH;
+
+      /* Camera/View Gizmo's - Allowed */
+      /* (See rationale in gpencil_paint.c -> gpencil_draw_modal()) */
+      case PAD0:
+      case PAD1:
+      case PAD2:
+      case PAD3:
+      case PAD4:
+      case PAD5:
+      case PAD6:
+      case PAD7:
+      case PAD8:
+      case PAD9:
+        return OPERATOR_PASS_THROUGH;
+
+      /* Unhandled event */
+      default:
+        break;
+    }
+  }
+
+  /* Redraw region? */
+  if (redraw_region) {
+    ED_region_tag_redraw(CTX_wm_region(C));
+  }
+
+  /* Redraw toolsettings (brush settings)? */
+  if (redraw_toolsettings) {
+    DEG_id_tag_update(&gso->gpd->id, ID_RECALC_GEOMETRY);
+    WM_event_add_notifier(C, NC_SCENE | ND_TOOLSETTINGS, NULL);
+  }
+
+  return OPERATOR_RUNNING_MODAL;
+}
+
+void GPENCIL_OT_weight_paint(wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Stroke Weight Paint";
+  ot->idname = "GPENCIL_OT_weight_paint";
+  ot->description = "Paint stroke points with a color";
+
+  /* api callbacks */
+  ot->exec = gp_weightpaint_brush_exec;
+  ot->invoke = gp_weightpaint_brush_invoke;
+  ot->modal = gp_weightpaint_brush_modal;
+  ot->cancel = gp_weightpaint_brush_exit;
+  ot->poll = gp_weightpaint_brush_poll;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_BLOCKING;
+
+  /* properties */
+  PropertyRNA *prop;
+  prop = RNA_def_collection_runtime(ot->srna, "stroke", &RNA_OperatorStrokeElement, "Stroke", "");
+  RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
+
+  prop = RNA_def_boolean(ot->srna, "wait_for_input", true, "Wait for Input", "");
+  RNA_def_property_flag(prop, PROP_HIDDEN | PROP_SKIP_SAVE);
+}