GPencil: Improve smooth operation

This patch makes the grease pencil smooth operation symmetric.
It also increases the performance a lot if strong smoothing is
required. Additionally there is an option for the position smooth
operation to keep the shape closer to the original for more iterations.

Since the result differs from the previous algorithm, versioning is used
to change the iterations and factor to match the old result.

Differential Revision: http://developer.blender.org/D14325

5 files changed, 45 insertions, 61 deletions

diff --git a/source/blender/editors/gpencil/gpencil_edit.c b/source/blender/editors/gpencil/gpencil_edit.c
index 8506e90191f..a8fb344f366 100644
--- a/source/blender/editors/gpencil/gpencil_edit.c
+++ b/source/blender/editors/gpencil/gpencil_edit.c
@@ -3924,31 +3924,36 @@ static void gpencil_smooth_stroke(bContext *C, wmOperator *op)
 
   GP_EDITABLE_STROKES_BEGIN (gpstroke_iter, C, gpl, gps) {
     if (gps->flag & GP_STROKE_SELECT) {
-      for (int r = 0; r < repeat; r++) {
+      /* TODO use `BKE_gpencil_stroke_smooth` when the weights are better used. */
+      bGPDstroke gps_old = *gps;
+      gps_old.points = (bGPDspoint *)MEM_dupallocN(gps->points);
+      /* Here the iteration needs to be done outside the smooth functions,
+       * as there are points that don't get smoothed. */
+      for (int n = 0; n < repeat; n++) {
         for (int i = 0; i < gps->totpoints; i++) {
-          bGPDspoint *pt = &gps->points[i];
-          if ((only_selected) && ((pt->flag & GP_SPOINT_SELECT) == 0)) {
+          if (only_selected && (gps->points[i].flag & GP_SPOINT_SELECT) == 0) {
             continue;
           }
 
-          /* perform smoothing */
+          /* Perform smoothing. */
           if (smooth_position) {
-            BKE_gpencil_stroke_smooth_point(gps, i, factor, false);
+            BKE_gpencil_stroke_smooth_point(&gps_old, i, factor, 1, false, false, gps);
           }
           if (smooth_strength) {
-            BKE_gpencil_stroke_smooth_strength(gps, i, factor);
+            BKE_gpencil_stroke_smooth_strength(&gps_old, i, factor, 1, gps);
           }
           if (smooth_thickness) {
-            /* thickness need to repeat process several times */
-            for (int r2 = 0; r2 < repeat * 2; r2++) {
-              BKE_gpencil_stroke_smooth_thickness(gps, i, 1.0f - factor);
-            }
+            BKE_gpencil_stroke_smooth_thickness(&gps_old, i, 1.0f - factor, 1, gps);
           }
           if (smooth_uv) {
-            BKE_gpencil_stroke_smooth_uv(gps, i, factor);
+            BKE_gpencil_stroke_smooth_uv(&gps_old, i, factor, 1, gps);
           }
         }
+        if (n < repeat - 1) {
+          memcpy(gps_old.points, gps->points, sizeof(bGPDspoint) * gps->totpoints);
+        }
       }
+      MEM_freeN(gps_old.points);
     }
   }
   GP_EDITABLE_STROKES_END(gpstroke_iter);
@@ -4926,10 +4931,10 @@ void GPENCIL_OT_stroke_smooth(wmOperatorType *ot)
   ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
 
   /* properties */
-  prop = RNA_def_int(ot->srna, "repeat", 1, 1, 50, "Repeat", "", 1, 20);
+  prop = RNA_def_int(ot->srna, "repeat", 2, 1, 1000, "Repeat", "", 1, 1000);
   RNA_def_property_flag(prop, PROP_SKIP_SAVE);
 
-  RNA_def_float(ot->srna, "factor", 0.5f, 0.0f, 2.0f, "Factor", "", 0.0f, 2.0f);
+  RNA_def_float(ot->srna, "factor", 1.0f, 0.0f, 2.0f, "Factor", "", 0.0f, 1.0f);
   RNA_def_boolean(ot->srna,
                   "only_selected",
                   true,
diff --git a/source/blender/editors/gpencil/gpencil_fill.c b/source/blender/editors/gpencil/gpencil_fill.c
index 45a2247c65e..8fc300412d9 100644
--- a/source/blender/editors/gpencil/gpencil_fill.c
+++ b/source/blender/editors/gpencil/gpencil_fill.c
@@ -1638,14 +1638,9 @@ static void gpencil_stroke_from_buffer(tGPDfill *tgpf)
     }
   }
 
-  /* smooth stroke */
-  float reduce = 0.0f;
-  float smoothfac = 1.0f;
-  for (int r = 0; r < 1; r++) {
-    for (int i = 0; i < gps->totpoints; i++) {
-      BKE_gpencil_stroke_smooth_point(gps, i, smoothfac - reduce, false);
-    }
-    reduce += 0.25f; /* reduce the factor */
+  /* Smooth stroke. No copy of the stroke since there only a minor improvement here. */
+  for (int i = 0; i < gps->totpoints; i++) {
+    BKE_gpencil_stroke_smooth_point(gps, i, 1.0f, 2, false, true, gps);
   }
 
   /* if axis locked, reproject to plane locked */
diff --git a/source/blender/editors/gpencil/gpencil_interpolate.c b/source/blender/editors/gpencil/gpencil_interpolate.c
index 65060e1bab5..8630b7f23d4 100644
--- a/source/blender/editors/gpencil/gpencil_interpolate.c
+++ b/source/blender/editors/gpencil/gpencil_interpolate.c
@@ -310,23 +310,6 @@ static void gpencil_stroke_pair_table(bContext *C,
   }
 }
 
-static void gpencil_interpolate_smooth_stroke(bGPDstroke *gps,
-                                              float smooth_factor,
-                                              int smooth_steps)
-{
-  if (smooth_factor == 0.0f) {
-    return;
-  }
-
-  float reduce = 0.0f;
-  for (int r = 0; r < smooth_steps; r++) {
-    for (int i = 0; i < gps->totpoints - 1; i++) {
-      BKE_gpencil_stroke_smooth_point(gps, i, smooth_factor - reduce, false);
-      BKE_gpencil_stroke_smooth_strength(gps, i, smooth_factor);
-    }
-    reduce += 0.25f; /* reduce the factor */
-  }
-}
 /* Perform interpolation */
 static void gpencil_interpolate_update_points(const bGPDstroke *gps_from,
                                               const bGPDstroke *gps_to,
@@ -553,7 +536,15 @@ static void gpencil_interpolate_set_points(bContext *C, tGPDinterpolate *tgpi)
 
       /* Update points position. */
       gpencil_interpolate_update_points(gps_from, gps_to, new_stroke, tgpil->factor);
-      gpencil_interpolate_smooth_stroke(new_stroke, tgpi->smooth_factor, tgpi->smooth_steps);
+      BKE_gpencil_stroke_smooth(new_stroke,
+                                tgpi->smooth_factor,
+                                tgpi->smooth_steps,
+                                true,
+                                true,
+                                false,
+                                false,
+                                true,
+                                NULL);
 
       /* Calc geometry data. */
       BKE_gpencil_stroke_geometry_update(gpd, new_stroke);
@@ -1385,7 +1376,8 @@ static int gpencil_interpolate_seq_exec(bContext *C, wmOperator *op)
 
         /* Update points position. */
         gpencil_interpolate_update_points(gps_from, gps_to, new_stroke, factor);
-        gpencil_interpolate_smooth_stroke(new_stroke, smooth_factor, smooth_steps);
+        BKE_gpencil_stroke_smooth(
+            new_stroke, smooth_factor, smooth_steps, true, true, false, false, true, NULL);
 
         /* Calc geometry data. */
         BKE_gpencil_stroke_geometry_update(gpd, new_stroke);
diff --git a/source/blender/editors/gpencil/gpencil_paint.c b/source/blender/editors/gpencil/gpencil_paint.c
index 18dc8d4bc72..93a4a784674 100644
--- a/source/blender/editors/gpencil/gpencil_paint.c
+++ b/source/blender/editors/gpencil/gpencil_paint.c
@@ -1197,29 +1197,21 @@ static void gpencil_stroke_newfrombuffer(tGPsdata *p)
       gpencil_subdivide_stroke(gpd, gps, subdivide);
     }
 
-    /* Smooth stroke after subdiv - only if there's something to do for each iteration,
-     * the factor is reduced to get a better smoothing
-     * without changing too much the original stroke. */
-    if ((brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) &&
-        (brush->gpencil_settings->draw_smoothfac > 0.0f)) {
-      float reduce = 0.0f;
-      for (int r = 0; r < brush->gpencil_settings->draw_smoothlvl; r++) {
-        for (i = 0; i < gps->totpoints - 1; i++) {
-          BKE_gpencil_stroke_smooth_point(
-              gps, i, brush->gpencil_settings->draw_smoothfac - reduce, false);
-          BKE_gpencil_stroke_smooth_strength(gps, i, brush->gpencil_settings->draw_smoothfac);
-        }
-        reduce += 0.25f; /* reduce the factor */
-      }
+    /* Smooth stroke after subdiv - only if there's something to do for each iteration.
+     * Keep the original stroke shape as much as possible. */
+    const float smoothfac = brush->gpencil_settings->draw_smoothfac;
+    const int iterations = brush->gpencil_settings->draw_smoothlvl;
+    if (brush->gpencil_settings->flag & GP_BRUSH_GROUP_SETTINGS) {
+      BKE_gpencil_stroke_smooth(gps, smoothfac, iterations, true, true, false, false, true, NULL);
     }
     /* If reproject the stroke using Stroke mode, need to apply a smooth because
      * the reprojection creates small jitter. */
     if (ts->gpencil_v3d_align & GP_PROJECT_DEPTH_STROKE) {
       float ifac = (float)brush->gpencil_settings->input_samples / 10.0f;
       float sfac = interpf(1.0f, 0.2f, ifac);
-      for (i = 0; i < gps->totpoints - 1; i++) {
-        BKE_gpencil_stroke_smooth_point(gps, i, sfac, false);
-        BKE_gpencil_stroke_smooth_strength(gps, i, sfac);
+      for (i = 0; i < gps->totpoints; i++) {
+        BKE_gpencil_stroke_smooth_point(gps, i, sfac, 2, false, true, gps);
+        BKE_gpencil_stroke_smooth_strength(gps, i, sfac, 2, gps);
       }
     }
 
diff --git a/source/blender/editors/gpencil/gpencil_sculpt_paint.c b/source/blender/editors/gpencil/gpencil_sculpt_paint.c
index 216971e514b..1e7159392e2 100644
--- a/source/blender/editors/gpencil/gpencil_sculpt_paint.c
+++ b/source/blender/editors/gpencil/gpencil_sculpt_paint.c
@@ -329,16 +329,16 @@ static bool gpencil_brush_smooth_apply(tGP_BrushEditData *gso,
 
   /* perform smoothing */
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_POSITION) {
-    BKE_gpencil_stroke_smooth_point(gps, pt_index, inf, false);
+    BKE_gpencil_stroke_smooth_point(gps, pt_index, inf, 2, false, false, gps);
   }
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_STRENGTH) {
-    BKE_gpencil_stroke_smooth_strength(gps, pt_index, inf);
+    BKE_gpencil_stroke_smooth_strength(gps, pt_index, inf, 2, gps);
   }
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_THICKNESS) {
-    BKE_gpencil_stroke_smooth_thickness(gps, pt_index, inf);
+    BKE_gpencil_stroke_smooth_thickness(gps, pt_index, inf, 2, gps);
   }
   if (gso->brush->gpencil_settings->sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_UV) {
-    BKE_gpencil_stroke_smooth_uv(gps, pt_index, inf);
+    BKE_gpencil_stroke_smooth_uv(gps, pt_index, inf, 2, gps);
   }
 
   return true;