Add cloth pressure vertex group and unlock cloth shrink values range

Introduced a way to specify cloth pressure force influence with a vertex
group. This will allow users to only have pressure affect certain parts
of the mesh.

In addition to this, the "shrink factor" is now also unlocked to allow
negative values and thus allowing the cloth mesh to grow as well.

Reviewed By: Jaques Lucke

Differential Revision: http://developer.blender.org/D6347

3 files changed, 69 insertions, 14 deletions

diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp b/source/blender/physics/intern/BPH_mass_spring.cpp
index 259eed88756..7521efa5cbd 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -76,18 +76,39 @@ static int cloth_count_nondiag_blocks(Cloth *cloth)
 
 static float cloth_calc_volume(ClothModifierData *clmd)
 {
-  /* calc the (closed) cloth volume */
+  /* Calculate the (closed) cloth volume. */
   Cloth *cloth = clmd->clothObject;
   const MVertTri *tri = cloth->tri;
   Implicit_Data *data = cloth->implicit;
   float vol = 0;
 
-  for (unsigned int i = 0; i < cloth->tri_num; i++) {
-    const MVertTri *vt = &tri[i];
-    vol += BPH_tri_tetra_volume_signed_6x(data, vt->tri[0], vt->tri[1], vt->tri[2]);
-  }
+  if (clmd->sim_parms->vgroup_pressure > 0) {
+    for (unsigned int i = 0; i < cloth->tri_num; i++) {
+      bool skip_face = false;
+      /* We have custom vertex weights for pressure. */
+      const MVertTri *vt = &tri[i];
+      for (unsigned int j = 0; j < 3; j++) {
+        /* If any weight is zero, don't take this face into account for volume calculation. */
+        ClothVertex *verts = clmd->clothObject->verts;
+
+        if (verts[vt->tri[j]].pressure_factor == 0.0f) {
+          skip_face = true;
+        }
+      }
+      if (skip_face) {
+        continue;
+      }
 
-  /* We need to divide by 6 to get the actual volume */
+      vol += BPH_tri_tetra_volume_signed_6x(data, vt->tri[0], vt->tri[1], vt->tri[2]);
+    }
+  }
+  else {
+    for (unsigned int i = 0; i < cloth->tri_num; i++) {
+      const MVertTri *vt = &tri[i];
+      vol += BPH_tri_tetra_volume_signed_6x(data, vt->tri[0], vt->tri[1], vt->tri[2]);
+    }
+  }
+  /* We need to divide by 6 to get the actual volume. */
   vol = vol / 6.0f;
 
   return vol;
@@ -634,8 +655,38 @@ static void cloth_calc_force(
     for (i = 0; i < cloth->tri_num; i++) {
       const MVertTri *vt = &tri[i];
       if (fabs(pressure_difference) > 1E-6f) {
-        BPH_mass_spring_force_pressure(
-            data, vt->tri[0], vt->tri[1], vt->tri[2], pressure_difference);
+        if (clmd->sim_parms->vgroup_pressure > 0) {
+          /* We have custom vertex weights for pressure. */
+          ClothVertex *verts = clmd->clothObject->verts;
+          int v1, v2, v3;
+          v1 = vt->tri[0];
+          v2 = vt->tri[1];
+          v3 = vt->tri[2];
+
+          float weights[3];
+          bool skip_face = false;
+
+          weights[0] = verts[v1].pressure_factor;
+          weights[1] = verts[v2].pressure_factor;
+          weights[2] = verts[v3].pressure_factor;
+          for (unsigned int j = 0; j < 3; j++) {
+            if (weights[j] == 0.0f) {
+              /* Exclude faces which has a zero weight vert. */
+              skip_face = true;
+              break;
+            }
+          }
+          if (skip_face) {
+            continue;
+          }
+
+          BPH_mass_spring_force_pressure(data, v1, v2, v3, pressure_difference, weights);
+        }
+        else {
+          float weights[3] = {1.0f, 1.0f, 1.0f};
+          BPH_mass_spring_force_pressure(
+              data, vt->tri[0], vt->tri[1], vt->tri[2], pressure_difference, weights);
+        }
       }
     }
   }
diff --git a/source/blender/physics/intern/implicit.h b/source/blender/physics/intern/implicit.h
index 82a3f61e1e1..490e727b5f2 100644
--- a/source/blender/physics/intern/implicit.h
+++ b/source/blender/physics/intern/implicit.h
@@ -184,8 +184,12 @@ bool BPH_mass_spring_force_spring_goal(struct Implicit_Data *data,
 
 float BPH_tri_tetra_volume_signed_6x(struct Implicit_Data *data, int v1, int v2, int v3);
 
-void BPH_mass_spring_force_pressure(
-    struct Implicit_Data *data, int v1, int v2, int v3, float pressure_difference);
+void BPH_mass_spring_force_pressure(struct Implicit_Data *data,
+                                    int v1,
+                                    int v2,
+                                    int v3,
+                                    float pressure_difference,
+                                    float weights[3]);
 
 /* ======== Hair Volumetric Forces ======== */
 
diff --git a/source/blender/physics/intern/implicit_blender.c b/source/blender/physics/intern/implicit_blender.c
index fa093f482f7..02d7fd50797 100644
--- a/source/blender/physics/intern/implicit_blender.c
+++ b/source/blender/physics/intern/implicit_blender.c
@@ -1489,7 +1489,7 @@ float BPH_tri_tetra_volume_signed_6x(Implicit_Data *data, int v1, int v2, int v3
 }
 
 void BPH_mass_spring_force_pressure(
-    Implicit_Data *data, int v1, int v2, int v3, float pressure_difference)
+    Implicit_Data *data, int v1, int v2, int v3, float pressure_difference, float weights[3])
 {
   float nor[3], area;
   float factor;
@@ -1500,9 +1500,9 @@ void BPH_mass_spring_force_pressure(
   factor = pressure_difference * area / 3.0f;
 
   /* add pressure to each of the face verts */
-  madd_v3_v3fl(data->F[v1], nor, factor);
-  madd_v3_v3fl(data->F[v2], nor, factor);
-  madd_v3_v3fl(data->F[v3], nor, factor);
+  madd_v3_v3fl(data->F[v1], nor, factor * weights[0]);
+  madd_v3_v3fl(data->F[v2], nor, factor * weights[1]);
+  madd_v3_v3fl(data->F[v3], nor, factor * weights[2]);
 }
 
 static void edge_wind_vertex(const float dir[3],