Modifiers: add invert vgroup weights options to operands of Mix modifier.

Please note that vertices which are in a vgroup are not affected by this
option (which means that affected vertices from 'selection' modes remain
the same). Only the weights of selected vertices get inverted.

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D7811

3 files changed, 34 insertions, 2 deletions

diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index e74f42f5c10..13972ae032d 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -1505,6 +1505,8 @@ enum {
 enum {
   MOD_WVG_MIX_INVERT_VGROUP_MASK = (1 << 0),
   MOD_WVG_MIX_WEIGHTS_NORMALIZE = (1 << 1),
+  MOD_WVG_MIX_INVERT_VGROUP_A = (1 << 2),
+  MOD_WVG_MIX_INVERT_VGROUP_B = (1 << 3),
 };
 
 typedef struct WeightVGProximityModifierData {
diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index 031d37bcbdf..f5a437b7892 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -5012,6 +5012,16 @@ static void rna_def_modifier_weightvgmix(BlenderRNA *brna)
   RNA_def_property_string_funcs(prop, NULL, NULL, "rna_WeightVGMixModifier_defgrp_name_b_set");
   RNA_def_property_update(prop, 0, "rna_Modifier_update");
 
+  prop = RNA_def_property(srna, "invert_vertex_group_a", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", MOD_WVG_MIX_INVERT_VGROUP_A);
+  RNA_def_property_ui_text(prop, "Invert Weights A", "Invert the influence of vertex group A");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "invert_vertex_group_b", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", MOD_WVG_MIX_INVERT_VGROUP_B);
+  RNA_def_property_ui_text(prop, "Invert Weights B", "Invert the influence of vertex group B");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
   prop = RNA_def_property(srna, "default_weight_a", PROP_FLOAT, PROP_FACTOR);
   RNA_def_property_range(prop, 0.0, 1.0f);
   RNA_def_property_ui_range(prop, 0.0, 1.0, 1, -1);
diff --git a/source/blender/modifiers/intern/MOD_weightvgmix.c b/source/blender/modifiers/intern/MOD_weightvgmix.c
index 57156aec5ec..a71b1d9d0e8 100644
--- a/source/blender/modifiers/intern/MOD_weightvgmix.c
+++ b/source/blender/modifiers/intern/MOD_weightvgmix.c
@@ -225,6 +225,16 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
   int i;
   const bool invert_vgroup_mask = (wmd->flag & MOD_WVG_MIX_INVERT_VGROUP_MASK) != 0;
   const bool do_normalize = (wmd->flag & MOD_WVG_MIX_WEIGHTS_NORMALIZE) != 0;
+
+  /*
+   * Note that we only invert the weight values within provided vgroups, the selection based on
+   * which vertice is affected because it belongs or not to a group remains unchanged.
+   * In other words, vertices not belonging to a group won't be affected, even though their
+   * inverted 'virtual' weight would be 1.0f.
+   */
+  const bool invert_vgroup_a = (wmd->flag & MOD_WVG_MIX_INVERT_VGROUP_A) != 0;
+  const bool invert_vgroup_b = (wmd->flag & MOD_WVG_MIX_INVERT_VGROUP_B) != 0;
+
   /* Flags. */
 #if 0
   const bool do_prev = (wmd->modifier.mode & eModifierMode_DoWeightPreview) != 0;
@@ -379,8 +389,18 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
   /* Mix weights. */
   for (i = 0; i < numIdx; i++) {
     float weight2;
-    org_w[i] = dw1[i] ? dw1[i]->weight : wmd->default_weight_a;
-    weight2 = dw2[i] ? dw2[i]->weight : wmd->default_weight_b;
+    if (invert_vgroup_a) {
+      org_w[i] = 1.0f - (dw1[i] ? dw1[i]->weight : wmd->default_weight_a);
+    }
+    else {
+      org_w[i] = dw1[i] ? dw1[i]->weight : wmd->default_weight_a;
+    }
+    if (invert_vgroup_b) {
+      weight2 = 1.0f - (dw2[i] ? dw2[i]->weight : wmd->default_weight_b);
+    }
+    else {
+      weight2 = dw2[i] ? dw2[i]->weight : wmd->default_weight_b;
+    }
 
     new_w[i] = mix_weight(org_w[i], weight2, wmd->mix_mode);
   }