Surface Deform modifier: add vertex group and strength control.

This commit aims to add functionality to the surface deform modifier that
gives more control and allows it to work better with the modifier stack.
* Maintains compatibility with older files. The default settings keep it
  so that the whole object is bound and vertex coordinates get overwritten
  as the modifier currently does.
* Turns the deformations from an absolute vertex coordinate overwrite into
  an additive offset from the vertex location before the modifier to the
  resulting bound deformation. This gives the ability to control the
  strength of the deformation and mix the deformation of the modifier
  with the modifier stack that comes before it.
* Also adds in a vertex group with the invert option. This is applied after
  the bind deformation is added. So the whole object is still bound to target,
  and the vertex group filters afterwards what parts get affected.
  I experimented with a version to only binds the geometry weighted to the
  vertex group, but that would break compatibility with old files.
  I may bring it in later as a separate option/mode for the surface deform.

With several fixes from @mont29.

Reviewed By: mont29

Differencial Revision: https://developer.blender.org/D6894

1 files changed, 99 insertions, 10 deletions

diff --git a/source/blender/modifiers/intern/MOD_surfacedeform.c b/source/blender/modifiers/intern/MOD_surfacedeform.c
index 57e7e2fa98b..d4fa2ea1f82 100644
--- a/source/blender/modifiers/intern/MOD_surfacedeform.c
+++ b/source/blender/modifiers/intern/MOD_surfacedeform.c
@@ -36,6 +36,8 @@
 #include "BKE_mesh_runtime.h"
 #include "BKE_modifier.h"
 
+#include "BKE_deform.h"
+
 #include "DEG_depsgraph.h"
 #include "DEG_depsgraph_query.h"
 
@@ -110,6 +112,8 @@ typedef struct SDefDeformData {
   const SDefVert *const bind_verts;
   float (*const targetCos)[3];
   float (*const vertexCos)[3];
+  float(*const weights);
+  float const strength;
 } SDefDeformData;
 
 /* Bind result values */
@@ -136,6 +140,19 @@ static void initData(ModifierData *md)
   smd->verts = NULL;
   smd->flags = 0;
   smd->falloff = 4.0f;
+  smd->strength = 1.0f;
+}
+
+static void requiredDataMask(Object *UNUSED(ob),
+                             ModifierData *md,
+                             CustomData_MeshMasks *r_cddata_masks)
+{
+  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
+
+  /* Ask for vertex groups if we need them. */
+  if (smd->defgrp_name[0] != '\0') {
+    r_cddata_masks->vmask |= CD_MASK_MDEFORMVERT;
+  }
 }
 
 static void freeData(ModifierData *md)
@@ -1123,9 +1140,16 @@ static void deformVert(void *__restrict userdata,
   const SDefBind *sdbind = data->bind_verts[index].binds;
   const int num_binds = data->bind_verts[index].numbinds;
   float *const vertexCos = data->vertexCos[index];
-  float norm[3], temp[3];
+  float norm[3], temp[3], offset[3];
+  const float weight = (data->weights != NULL) ? data->weights[index] : 1.0f;
 
-  zero_v3(vertexCos);
+  /* Check if this vertex will be deformed. If it is not deformed we return and avoid
+   * unneccessary calculations. */
+  if (weight == 0.0f) {
+    return;
+  }
+
+  zero_v3(offset);
 
   /* Allocate a `coords_buffer` that fits all the temp-data. */
   int max_verts = 0;
@@ -1170,8 +1194,13 @@ static void deformVert(void *__restrict userdata,
     /* Apply normal offset (generic for all modes) */
     madd_v3_v3fl(temp, norm, sdbind->normal_dist);
 
-    madd_v3_v3fl(vertexCos, temp, sdbind->influence);
+    madd_v3_v3fl(offset, temp, sdbind->influence);
   }
+  /* Subtract the vertex coord to get the deformation offset. */
+  sub_v3_v3(offset, vertexCos);
+
+  /* Add the offset to start coord multiplied by the strength and weight values. */
+  madd_v3_v3fl(vertexCos, offset, data->strength * weight);
   MEM_freeN(coords_buffer);
 }
 
@@ -1179,7 +1208,8 @@ static void surfacedeformModifier_do(ModifierData *md,
                                      const ModifierEvalContext *ctx,
                                      float (*vertexCos)[3],
                                      uint numverts,
-                                     Object *ob)
+                                     Object *ob,
+                                     Mesh *mesh)
 {
   SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
   Mesh *target;
@@ -1238,11 +1268,44 @@ static void surfacedeformModifier_do(ModifierData *md,
     return;
   }
 
+  /* Early out if modifier would not affect input at all - still *after* the sanity checks (and
+   * potential binding) above.
+   */
+  if (smd->strength == 0.0f) {
+    return;
+  }
+
+  int defgrp_index;
+  MDeformVert *dvert;
+  MOD_get_vgroup(ob, mesh, smd->defgrp_name, &dvert, &defgrp_index);
+  float *weights = NULL;
+  const bool invert_group = (smd->flags & MOD_SDEF_INVERT_VGROUP) != 0;
+
+  if (defgrp_index != -1) {
+    dvert = CustomData_duplicate_referenced_layer(&mesh->vdata, CD_MDEFORMVERT, mesh->totvert);
+    /* If no vertices were ever added to an object's vgroup, dvert might be NULL. */
+    if (dvert == NULL) {
+      /* Add a valid data layer! */
+      dvert = CustomData_add_layer(&mesh->vdata, CD_MDEFORMVERT, CD_CALLOC, NULL, mesh->totvert);
+    }
+
+    if (dvert) {
+      weights = MEM_calloc_arrayN((size_t)numverts, sizeof(*weights), __func__);
+      MDeformVert *dv = dvert;
+      for (uint i = 0; i < numverts; i++, dv++) {
+        weights[i] = invert_group ? (1.0f - BKE_defvert_find_weight(dv, defgrp_index)) :
+                                    BKE_defvert_find_weight(dv, defgrp_index);
+      }
+    }
+  }
+
   /* Actual vertex location update starts here */
   SDefDeformData data = {
       .bind_verts = smd->verts,
       .targetCos = MEM_malloc_arrayN(tnumverts, sizeof(float[3]), "SDefTargetVertArray"),
       .vertexCos = vertexCos,
+      .weights = weights,
+      .strength = smd->strength,
   };
 
   if (data.targetCos != NULL) {
@@ -1259,25 +1322,51 @@ static void surfacedeformModifier_do(ModifierData *md,
 
     MEM_freeN(data.targetCos);
   }
+
+  MEM_SAFE_FREE(weights);
 }
 
 static void deformVerts(ModifierData *md,
                         const ModifierEvalContext *ctx,
-                        Mesh *UNUSED(mesh),
+                        Mesh *mesh,
                         float (*vertexCos)[3],
                         int numVerts)
 {
-  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object);
+  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
+  Mesh *mesh_src = NULL;
+
+  if (smd->defgrp_name[0] != '\0') {
+    /* Only need to use mesh_src when a vgroup is used. */
+    mesh_src = MOD_deform_mesh_eval_get(ctx->object, NULL, mesh, NULL, numVerts, false, false);
+  }
+
+  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object, mesh_src);
+
+  if (!ELEM(mesh_src, NULL, mesh)) {
+    BKE_id_free(NULL, mesh_src);
+  }
 }
 
 static void deformVertsEM(ModifierData *md,
                           const ModifierEvalContext *ctx,
-                          struct BMEditMesh *UNUSED(editData),
-                          Mesh *UNUSED(mesh),
+                          struct BMEditMesh *em,
+                          Mesh *mesh,
                           float (*vertexCos)[3],
                           int numVerts)
 {
-  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object);
+  SurfaceDeformModifierData *smd = (SurfaceDeformModifierData *)md;
+  Mesh *mesh_src = NULL;
+
+  if (smd->defgrp_name[0] != '\0') {
+    /* Only need to use mesh_src when a vgroup is used. */
+    mesh_src = MOD_deform_mesh_eval_get(ctx->object, em, mesh, NULL, numVerts, false, false);
+  }
+
+  surfacedeformModifier_do(md, ctx, vertexCos, numVerts, ctx->object, mesh_src);
+
+  if (!ELEM(mesh_src, NULL, mesh)) {
+    BKE_id_free(NULL, mesh_src);
+  }
 }
 
 static bool isDisabled(const Scene *UNUSED(scene), ModifierData *md, bool UNUSED(useRenderParams))
@@ -1309,7 +1398,7 @@ ModifierTypeInfo modifierType_SurfaceDeform = {
     /* applyModifier */ NULL,
 
     /* initData */ initData,
-    /* requiredDataMask */ NULL,
+    /* requiredDataMask */ requiredDataMask,
     /* freeData */ freeData,
     /* isDisabled */ isDisabled,
     /* updateDepsgraph */ updateDepsgraph,