GPencil: Improve Fill Tool speed (6 times faster) in complex files

There was a double loop when drawing the offscreen data for the fill tool. This loop did an exponential drawing, slowing a lot the process.

For example, one file was using 7.39 seconds and now use 1.20 or less to do the same process.

The fix is more noticeable with big files, reducing exponentially the time used by the tool. For very simple files the speed change can be unnoticeable.

Aso fixed a hidden bug with stroke opacity that it was unnoticeable due the double loop.

1 files changed, 32 insertions, 9 deletions

diff --git a/source/blender/editors/gpencil/drawgpencil.c b/source/blender/editors/gpencil/drawgpencil.c
index c54598fd549..76e13ec4eb5 100644
--- a/source/blender/editors/gpencil/drawgpencil.c
+++ b/source/blender/editors/gpencil/drawgpencil.c
@@ -121,9 +121,15 @@ static void gp_set_point_uniform_color(const bGPDspoint *pt, const float ink[4])
   immUniformColor3fvAlpha(ink, alpha);
 }
 
-static void gp_set_point_varying_color(const bGPDspoint *pt, const float ink[4], uint attr_id)
+static void gp_set_point_varying_color(const bGPDspoint *pt,
+                                       const float ink[4],
+                                       uint attr_id,
+                                       bool fix_strength)
 {
   float alpha = ink[3] * pt->strength;
+  if ((fix_strength) && (alpha >= 0.1f)) {
+    alpha = 1.0f;
+  }
   CLAMP(alpha, GPENCIL_STRENGTH_MIN, 1.0f);
   immAttr4ub(attr_id, F2UB(ink[0]), F2UB(ink[1]), F2UB(ink[2]), F2UB(alpha));
 }
@@ -186,7 +192,7 @@ static void gp_draw_stroke_volumetric_2d(const bGPDspoint *points,
     mul_v3_m4v3(fpt, diff_mat, &pt->x);
     gp_calc_2d_stroke_fxy(fpt, sflag, offsx, offsy, winx, winy, co);
 
-    gp_set_point_varying_color(pt, ink, color);
+    gp_set_point_varying_color(pt, ink, color, false);
     immAttr1f(size, pt->pressure * thickness); /* TODO: scale based on view transform */
     immVertex2f(pos, co[0], co[1]);
   }
@@ -214,7 +220,7 @@ static void gp_draw_stroke_volumetric_3d(const bGPDspoint *points,
 
   const bGPDspoint *pt = points;
   for (int i = 0; i < totpoints && pt; i++, pt++) {
-    gp_set_point_varying_color(pt, ink, color);
+    gp_set_point_varying_color(pt, ink, color, false);
     /* TODO: scale based on view transform */
     immAttr1f(size, pt->pressure * thickness);
     /* we can adjust size in vertex shader based on view/projection! */
@@ -576,7 +582,7 @@ static void gp_draw_stroke_3d(tGPDdraw *tgpw, short thickness, const float ink[4
   for (int i = 0; i < totpoints; i++, pt++) {
     /* first point for adjacency (not drawn) */
     if (i == 0) {
-      gp_set_point_varying_color(points, ink, attr_id.color);
+      gp_set_point_varying_color(points, ink, attr_id.color, (bool)tgpw->is_fill_stroke);
 
       if ((cyclic) && (totpoints > 2)) {
         immAttr1f(attr_id.thickness, max_ff((points + totpoints - 1)->pressure * thickness, 1.0f));
@@ -589,7 +595,7 @@ static void gp_draw_stroke_3d(tGPDdraw *tgpw, short thickness, const float ink[4
       immVertex3fv(attr_id.pos, fpt);
     }
     /* set point */
-    gp_set_point_varying_color(pt, ink, attr_id.color);
+    gp_set_point_varying_color(pt, ink, attr_id.color, (bool)tgpw->is_fill_stroke);
     immAttr1f(attr_id.thickness, max_ff(pt->pressure * thickness, 1.0f));
     mul_v3_m4v3(fpt, tgpw->diff_mat, &pt->x);
     immVertex3fv(attr_id.pos, fpt);
@@ -608,7 +614,9 @@ static void gp_draw_stroke_3d(tGPDdraw *tgpw, short thickness, const float ink[4
   }
   /* last adjacency point (not drawn) */
   else {
-    gp_set_point_varying_color(points + totpoints - 2, ink, attr_id.color);
+    gp_set_point_varying_color(
+        points + totpoints - 2, ink, attr_id.color, (bool)tgpw->is_fill_stroke);
+
     immAttr1f(attr_id.thickness, max_ff((points + totpoints - 2)->pressure * thickness, 1.0f));
     mul_v3_m4v3(fpt, tgpw->diff_mat, &(points + totpoints - 2)->x);
     immVertex3fv(attr_id.pos, fpt);
@@ -693,7 +701,7 @@ static void gp_draw_stroke_2d(const bGPDspoint *points,
       pthick = (pt1->pressure * thickness * scalefac);
 
       /* color of point */
-      gp_set_point_varying_color(pt1, ink, attr_id.color);
+      gp_set_point_varying_color(pt1, ink, attr_id.color, false);
 
       /* if the first segment, start of segment is segment's normal */
       if (i == 0) {
@@ -768,7 +776,7 @@ static void gp_draw_stroke_2d(const bGPDspoint *points,
         pthick = (pt2->pressure * thickness * scalefac);
 
         /* color of point */
-        gp_set_point_varying_color(pt2, ink, attr_id.color);
+        gp_set_point_varying_color(pt2, ink, attr_id.color, false);
 
         /* calculate points for end of segment */
         mt[0] = m2[0] * pthick;
@@ -861,7 +869,9 @@ static void gp_draw_strokes(tGPDdraw *tgpw)
 
   GPU_enable_program_point_size();
 
-  for (bGPDstroke *gps = tgpw->t_gpf->strokes.first; gps; gps = gps->next) {
+  bGPDstroke *gps_init = (tgpw->gps) ? tgpw->gps : tgpw->t_gpf->strokes.first;
+
+  for (bGPDstroke *gps = gps_init; gps; gps = gps->next) {
     /* check if stroke can be drawn */
     if (gp_can_draw_stroke(gps, tgpw->dflag) == false) {
       continue;
@@ -955,6 +965,14 @@ static void gp_draw_strokes(tGPDdraw *tgpw)
           copy_v4_v4(ink, tcolor);
         }
       }
+
+      /* if used for fill, set opacity to 1 */
+      if (tgpw->is_fill_stroke) {
+        if (ink[3] >= GPENCIL_ALPHA_OPACITY_THRESH) {
+          ink[3] = 1.0f;
+        }
+      }
+
       if (gp_style->mode == GP_STYLE_MODE_DOTS) {
         /* volumetric stroke drawing */
         if (tgpw->disable_fill != 1) {
@@ -1080,6 +1098,10 @@ static void gp_draw_strokes(tGPDdraw *tgpw)
         }
       }
     }
+    /* if only one stroke, exit from loop */
+    if (tgpw->gps) {
+      break;
+    }
   }
 
   GPU_disable_program_point_size();
@@ -1126,6 +1148,7 @@ void ED_gp_draw_interpolation(const bContext *C, tGPDinterpolate *tgpi, const in
       tgpw.gpl = tgpil->gpl;
       tgpw.gpf = tgpil->interFrame;
       tgpw.t_gpf = tgpil->interFrame;
+      tgpw.gps = NULL;
 
       tgpw.lthick = tgpil->gpl->line_change;
       tgpw.opacity = 1.0;