GPencil: Add skip option to envelope modifier

This patch adds an option to only use every n-th segment of the
envelope result. This can be used to reduce the complexity of the
result.

Differential Revision: http://developer.blender.org/D14503

4 files changed, 59 insertions, 34 deletions

diff --git a/source/blender/gpencil_modifiers/intern/MOD_gpencilenvelope.c b/source/blender/gpencil_modifiers/intern/MOD_gpencilenvelope.c
index f8ac8d95493..d9881f5b7ae 100644
--- a/source/blender/gpencil_modifiers/intern/MOD_gpencilenvelope.c
+++ b/source/blender/gpencil_modifiers/intern/MOD_gpencilenvelope.c
@@ -332,18 +332,17 @@ static void add_stroke(Object *ob,
                        bGPDstroke *gps,
                        const int point_index,
                        const int connection_index,
-                       const int size,
+                       const int size2,
+                       const int size1,
                        const int mat_nr,
                        const float thickness,
                        const float strength,
                        ListBase *results)
 {
+  const int size = size1 + size2;
   bGPdata *gpd = ob->data;
   bGPDstroke *gps_dst = BKE_gpencil_stroke_new(mat_nr, size, gps->thickness);
 
-  const int size1 = size == 4 ? 2 : 1;
-  const int size2 = size - size1;
-
   memcpy(&gps_dst->points[0], &gps->points[connection_index], size1 * sizeof(bGPDspoint));
   memcpy(&gps_dst->points[size1], &gps->points[point_index], size2 * sizeof(bGPDspoint));
 
@@ -369,35 +368,36 @@ static void add_stroke_cyclic(Object *ob,
                               bGPDstroke *gps,
                               const int point_index,
                               const int connection_index,
+                              const int size,
                               const int mat_nr,
                               const float thickness,
                               const float strength,
                               ListBase *results)
 {
   bGPdata *gpd = ob->data;
-  bGPDstroke *gps_dst = BKE_gpencil_stroke_new(mat_nr, 4, gps->thickness);
+  bGPDstroke *gps_dst = BKE_gpencil_stroke_new(mat_nr, size * 2, gps->thickness);
+  if (gps->dvert != NULL) {
+    gps_dst->dvert = MEM_malloc_arrayN(size * 2, sizeof(MDeformVert), __func__);
+  }
 
-  int connection_index2 = (connection_index + 1) % gps->totpoints;
-  int point_index2 = (point_index + 1) % gps->totpoints;
+  for (int i = 0; i < size; i++) {
+    int a = (connection_index + i) % gps->totpoints;
+    int b = (point_index + i) % gps->totpoints;
 
-  gps_dst->points[0] = gps->points[connection_index];
-  gps_dst->points[1] = gps->points[connection_index2];
-  gps_dst->points[2] = gps->points[point_index];
-  gps_dst->points[3] = gps->points[point_index2];
-  for (int i = 0; i < 4; i++) {
+    gps_dst->points[i] = gps->points[a];
+    gps_dst->points[size + i] = gps->points[b];
+
+    if (gps->dvert != NULL) {
+      BKE_defvert_array_copy(&gps_dst->dvert[i], &gps->dvert[a], 1);
+      BKE_defvert_array_copy(&gps_dst->dvert[size + i], &gps->dvert[b], 1);
+    }
+  }
+  for (int i = 0; i < size * 2; i++) {
     gps_dst->points[i].pressure *= thickness;
     gps_dst->points[i].strength *= strength;
     memset(&gps_dst->points[i].runtime, 0, sizeof(bGPDspoint_Runtime));
   }
 
-  if (gps->dvert != NULL) {
-    gps_dst->dvert = MEM_malloc_arrayN(4, sizeof(MDeformVert), __func__);
-    BKE_defvert_array_copy(&gps_dst->dvert[0], &gps->dvert[connection_index], 1);
-    BKE_defvert_array_copy(&gps_dst->dvert[1], &gps->dvert[connection_index2], 1);
-    BKE_defvert_array_copy(&gps_dst->dvert[2], &gps->dvert[point_index], 1);
-    BKE_defvert_array_copy(&gps_dst->dvert[3], &gps->dvert[point_index2], 1);
-  }
-
   BLI_addtail(results, gps_dst);
 
   /* Calc geometry data. */
@@ -459,31 +459,41 @@ static void generate_geometry(GpencilModifierData *md, Object *ob, bGPDlayer *gp
 
     const int mat_nr = mmd->mat_nr < 0 ? gps->mat_nr : min_ii(mmd->mat_nr, ob->totcol - 1);
     if (mmd->mode == GP_ENVELOPE_FILLS) {
+      const int skip = min_ii(mmd->skip, min_ii(mmd->spread / 2, gps->totpoints - 2));
       if (gps->flag & GP_STROKE_CYCLIC) {
         for (int i = 0; i < gps->totpoints; i++) {
-          const int connection_index = (i + mmd->spread) % gps->totpoints;
-          add_stroke_cyclic(
-              ob, gps, i, connection_index, mat_nr, mmd->thickness, mmd->strength, &duplicates);
+          const int connection_index = (i + mmd->spread - skip) % gps->totpoints;
+          add_stroke_cyclic(ob,
+                            gps,
+                            i,
+                            connection_index,
+                            2 + skip,
+                            mat_nr,
+                            mmd->thickness,
+                            mmd->strength,
+                            &duplicates);
+          i += mmd->skip;
         }
       }
       else {
-        for (int i = 1; i < gps->totpoints - 1 && i < mmd->spread + 1; i++) {
-          add_stroke(ob, gps, i, 0, 3, mat_nr, mmd->thickness, mmd->strength, &duplicates);
-        }
-        for (int i = 0; i < gps->totpoints - 1; i++) {
-          const int connection_index = min_ii(i + mmd->spread, gps->totpoints - 1);
-          const int size = i == gps->totpoints - 2               ? 2 :
-                           connection_index < gps->totpoints - 1 ? 4 :
-                                                                   3;
+        for (int i = -mmd->spread + skip; i < gps->totpoints - 1; i++) {
+          const int point_index = max_ii(0, i);
+          const int connection_index = min_ii(i + mmd->spread + 1, gps->totpoints - 1);
+          const int size1 = min_ii(2 + skip,
+                                   min_ii(point_index + 1, gps->totpoints - point_index));
+          const int size2 = min_ii(
+              2 + skip, min_ii(connection_index + 1, gps->totpoints - connection_index));
           add_stroke(ob,
                      gps,
-                     i,
-                     connection_index,
-                     size,
+                     point_index,
+                     connection_index + 1 - size2,
+                     size1,
+                     size2,
                      mat_nr,
                      mmd->thickness,
                      mmd->strength,
                      &duplicates);
+          i += mmd->skip;
         }
       }
       BLI_remlink(&gpf->strokes, gps);
@@ -496,6 +506,7 @@ static void generate_geometry(GpencilModifierData *md, Object *ob, bGPDlayer *gp
           const int connection_index = (i + 1 + mmd->spread) % gps->totpoints;
           add_stroke_simple(
               ob, gps, i, connection_index, mat_nr, mmd->thickness, mmd->strength, &duplicates);
+          i += mmd->skip;
         }
       }
       else {
@@ -509,6 +520,7 @@ static void generate_geometry(GpencilModifierData *md, Object *ob, bGPDlayer *gp
                             mmd->thickness,
                             mmd->strength,
                             &duplicates);
+          i += mmd->skip;
         }
       }
     }
@@ -585,6 +597,7 @@ static void panel_draw(const bContext *UNUSED(C), Panel *panel)
   if (mode != GP_ENVELOPE_DEFORM) {
     uiItemR(layout, ptr, "strength", 0, NULL, ICON_NONE);
     uiItemR(layout, ptr, "mat_nr", 0, NULL, ICON_NONE);
+    uiItemR(layout, ptr, "skip", 0, NULL, ICON_NONE);
   }
 
   gpencil_modifier_panel_end(layout, ptr);
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_defaults.h b/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
index 9d14ca039ac..750f97bb3c6 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_defaults.h
@@ -373,6 +373,7 @@
     .mat_nr = -1, \
     .thickness = 1.0f, \
     .strength = 1.0f, \
+    .skip = 0, \
   }
 
 
diff --git a/source/blender/makesdna/DNA_gpencil_modifier_types.h b/source/blender/makesdna/DNA_gpencil_modifier_types.h
index 6603ed1a078..b0e7342c9cb 100644
--- a/source/blender/makesdna/DNA_gpencil_modifier_types.h
+++ b/source/blender/makesdna/DNA_gpencil_modifier_types.h
@@ -1168,10 +1168,14 @@ typedef struct EnvelopeGpencilModifierData {
   float thickness;
   /** Strength multiplier for the new strokes. */
   float strength;
+  /** Number of points to skip over. */
+  int skip;
   /** Custom index for passes. */
   int layer_pass;
   /* Length of the envelope effect. */
   int spread;
+
+  char _pad[4];
 } EnvelopeGpencilModifierData;
 
 typedef enum eEnvelopeGpencil_Flag {
diff --git a/source/blender/makesrna/intern/rna_gpencil_modifier.c b/source/blender/makesrna/intern/rna_gpencil_modifier.c
index b09d8a4738d..04a9a6b169e 100644
--- a/source/blender/makesrna/intern/rna_gpencil_modifier.c
+++ b/source/blender/makesrna/intern/rna_gpencil_modifier.c
@@ -4126,6 +4126,13 @@ static void rna_def_modifier_gpencilenvelope(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Strength", "Multiplier for the strength of the new strokes");
   RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
 
+  prop = RNA_def_property(srna, "skip", PROP_INT, PROP_NONE);
+  RNA_def_property_int_sdna(prop, NULL, "skip");
+  RNA_def_property_range(prop, 0, INT_MAX);
+  RNA_def_property_ui_text(
+      prop, "Skip Segments", "The number of generated segments to skip to reduce complexity");
+  RNA_def_property_update(prop, 0, "rna_GpencilModifier_update");
+
   prop = RNA_def_property(srna, "invert_layers", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flag", GP_ENVELOPE_INVERT_LAYER);
   RNA_def_property_ui_text(prop, "Inverse Layers", "Inverse filter");