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],