Modifiers: Corrective Smooth modifier, new Scale parameter

When scaling the root bone of a rig to apply a global scale, the
corrective smooth modifier results in wrong deformation due to incorrect
scaling. The delta calculations are not taking into account any scale
value.

To fix it, a scale property is added to the modifier, allowing to set
manually the scale value for the deltas by simply multiplying the
vectors by this value. There is a similar implementation in Maya's Delta
Mush deformer. This property can be for example driven by the scale of
the root bone of the rig, to dynamically update when the animator scale
this bone.

Reviewed By: brecht, sybren

Differential Revision: https://developer.blender.org/D6622

release/scripts/startup/bl_ui/properties_data_modifier.py

@@ -1677,7 +1677,7 @@ class DATA_PT_modifiers(ModifierButtonsPanel, Panel):
 
         layout.prop(md, "factor", text="Factor")
         layout.prop(md, "iterations")
-
+        layout.prop(md, "scale")
         row = layout.row()
         row.prop(md, "smooth_type")
 

source/blender/blenloader/intern/versioning_280.c

@@ -4819,5 +4819,17 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
         br->automasking_boundary_edges_propagation_steps = 1;
       }
     }
+
+    /* Corrective smooth modifier scale*/
+    if (!DNA_struct_elem_find(fd->filesdna, "CorrectiveSmoothModifierData", "float", "scale")) {
+      for (Object *ob = bmain->objects.first; ob; ob = ob->id.next) {
+        for (ModifierData *md = ob->modifiers.first; md; md = md->next) {
+          if (md->type == eModifierType_CorrectiveSmooth) {
+            CorrectiveSmoothModifierData *csmd = (CorrectiveSmoothModifierData *)md;
+            csmd->scale = 1.0f;
+          }
+        }
+      }
+    }
   }
 }

source/blender/makesdna/DNA_modifier_types.h

@@ -1684,10 +1684,10 @@ typedef struct CorrectiveSmoothDeltaCache {
 
   /* Value of settings when creating the cache.
    * These are used to check if the cache should be recomputed. */
-  float lambda;
+  float lambda, scale;
   short repeat, flag;
   char smooth_type, rest_source;
-  char _pad[2];
+  char _pad[6];
 } CorrectiveSmoothDeltaCache;
 
 typedef struct CorrectiveSmoothModifierData {
@@ -1700,10 +1700,10 @@ typedef struct CorrectiveSmoothModifierData {
   /* note: -1 is used to bind */
   unsigned int bind_coords_num;
 
-  float lambda;
+  float lambda, scale;
   short repeat, flag;
   char smooth_type, rest_source;
-  char _pad[2];
+  char _pad[6];
 
   /** MAX_VGROUP_NAME. */
   char defgrp_name[64];

source/blender/makesrna/intern/rna_modifier.c

@@ -3109,6 +3109,13 @@ static void rna_def_modifier_correctivesmooth(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Repeat", "");
   RNA_def_property_update(prop, 0, "rna_CorrectiveSmoothModifier_update");
 
+  prop = RNA_def_property(srna, "scale", PROP_FLOAT, PROP_FACTOR);
+  RNA_def_property_float_sdna(prop, NULL, "scale");
+  RNA_def_property_range(prop, -FLT_MAX, FLT_MAX);
+  RNA_def_property_ui_range(prop, 0.0, 10.0, 5, 3);
+  RNA_def_property_ui_text(prop, "Scale", "Compensate for scale applied by other modifiers");
+  RNA_def_property_update(prop, 0, "rna_CorrectiveSmoothModifier_update");
+
   prop = RNA_def_property(srna, "rest_source", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_sdna(prop, NULL, "rest_source");
   RNA_def_property_enum_items(prop, modifier_rest_source_items);

source/blender/modifiers/intern/MOD_correctivesmooth.c

@@ -64,6 +64,7 @@ static void initData(ModifierData *md)
   csmd->bind_coords_num = 0;
 
   csmd->lambda = 0.5f;
+  csmd->scale = 1.0f;
   csmd->repeat = 5;
   csmd->flag = 0;
   csmd->smooth_type = MOD_CORRECTIVESMOOTH_SMOOTH_SIMPLE;
@@ -696,7 +697,7 @@ static void correctivesmooth_modifier_do(ModifierData *md,
     uint i;
 
     float(*tangent_spaces)[3][3];
-
+    const float scale = csmd->scale;
     /* calloc, since values are accumulated */
     tangent_spaces = MEM_calloc_arrayN(numVerts, sizeof(float[3][3]), __func__);
 
@@ -710,7 +711,7 @@ static void correctivesmooth_modifier_do(ModifierData *md,
 #endif
 
       mul_v3_m3v3(delta, tangent_spaces[i], csmd->delta_cache.deltas[i]);
-      add_v3_v3(vertexCos[i], delta);
+      madd_v3_v3fl(vertexCos[i], delta, scale);
     }
 
     MEM_freeN(tangent_spaces);