Modifiers: Explode modifier add invert vgroup option

Adds the invert vgroup option to the Explode modifier.

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D6844

4 files changed, 13 insertions, 2 deletions

diff --git a/release/scripts/startup/bl_ui/properties_data_modifier.py b/release/scripts/startup/bl_ui/properties_data_modifier.py
index 69cd8a96f99..1926e4bcae9 100644
--- a/release/scripts/startup/bl_ui/properties_data_modifier.py
+++ b/release/scripts/startup/bl_ui/properties_data_modifier.py
@@ -423,7 +423,9 @@ class DATA_PT_modifiers(ModifierButtonsPanel, Panel):
 
         col = split.column()
         col.label(text="Vertex Group:")
-        col.prop_search(md, "vertex_group", ob, "vertex_groups", text="")
+        row = col.row(align=True)
+        row.prop_search(md, "vertex_group", ob, "vertex_groups", text="")
+        row.prop(md, "invert_vertex_group", text="", icon='ARROW_LEFTRIGHT')
         sub = col.column()
         sub.active = bool(md.vertex_group)
         sub.prop(md, "protect")
diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 20ea798a2fa..502b66536fd 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -977,6 +977,7 @@ typedef enum {
   eExplodeFlag_Unborn = (1 << 3),
   eExplodeFlag_Alive = (1 << 4),
   eExplodeFlag_Dead = (1 << 5),
+  eExplodeFlag_INVERT_VGROUP = (1 << 6),
 } ExplodeModifierFlag;
 
 typedef struct ExplodeModifierData {
diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index 8063c5b80c4..eafc5b5407e 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -3600,6 +3600,11 @@ static void rna_def_modifier_explode(BlenderRNA *brna)
   RNA_def_property_string_maxlength(prop, MAX_CUSTOMDATA_LAYER_NAME);
   RNA_def_property_ui_text(prop, "Particle UV", "UV map to change with particle age");
   RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "invert_vertex_group", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", eExplodeFlag_INVERT_VGROUP);
+  RNA_def_property_ui_text(prop, "Invert", "Invert vertex group influence");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
 }
 
 static void rna_def_modifier_cloth(BlenderRNA *brna)
diff --git a/source/blender/modifiers/intern/MOD_explode.c b/source/blender/modifiers/intern/MOD_explode.c
index 88e45f652a0..26a353b4235 100644
--- a/source/blender/modifiers/intern/MOD_explode.c
+++ b/source/blender/modifiers/intern/MOD_explode.c
@@ -97,6 +97,7 @@ static void createFacepa(ExplodeModifierData *emd, ParticleSystemModifierData *p
   float center[3], co[3];
   int *facepa = NULL, *vertpa = NULL, totvert = 0, totface = 0, totpart = 0;
   int i, p, v1, v2, v3, v4 = 0;
+  const bool invert_vgroup = (emd->flag & eExplodeFlag_INVERT_VGROUP) != 0;
 
   mvert = mesh->mvert;
   mface = mesh->mface;
@@ -129,7 +130,9 @@ static void createFacepa(ExplodeModifierData *emd, ParticleSystemModifierData *p
       for (i = 0; i < totvert; i++, dvert++) {
         float val = BLI_rng_get_float(rng);
         val = (1.0f - emd->protect) * val + emd->protect * 0.5f;
-        if (val < defvert_find_weight(dvert, defgrp_index)) {
+        const float weight = invert_vgroup ? 1.0f - defvert_find_weight(dvert, defgrp_index) :
+                                             defvert_find_weight(dvert, defgrp_index);
+        if (val < weight) {
           vertpa[i] = -1;
         }
       }