Fix T30941: Add cloth air pressure simulation

This adds some basic simulation of internal air pressure inside of
closed cloth mesh objects.

Reviewed By: Jacques Lucke

Differential Revision: http://developer.blender.org/D5473

release/scripts/startup/bl_ui/properties_physics_cloth.py

@@ -161,6 +161,42 @@ class PHYSICS_PT_cloth_damping(PhysicButtonsPanel, Panel):
         col.prop(cloth, "bending_damping", text="Bending")
 
 
+class PHYSICS_PT_cloth_pressure(PhysicButtonsPanel, Panel):
+    bl_label = "Pressure"
+    bl_parent_id = 'PHYSICS_PT_cloth_physical_properties'
+    COMPAT_ENGINES = {'BLENDER_RENDER', 'BLENDER_EEVEE', 'BLENDER_WORKBENCH'}
+
+    def draw_header(self, context):
+        cloth = context.cloth.settings
+
+        self.layout.active = cloth_panel_enabled(context.cloth)
+        self.layout.prop(cloth, "use_pressure", text="")
+
+    def draw(self, context):
+        layout = self.layout
+        layout.use_property_split = True
+
+        cloth = context.cloth.settings
+        md = context.cloth
+
+        layout.active = cloth.use_pressure and cloth_panel_enabled(md)
+
+        flow = layout.grid_flow(row_major=False, columns=0, even_columns=True, even_rows=False, align=True)
+
+        col = flow.column()
+        col.prop(cloth, "uniform_pressure_force")
+
+        col = flow.column()
+        col.prop(cloth, "use_pressure_volume", text="Custom volume")
+
+        col = flow.column()
+        col.active = cloth.use_pressure_volume
+        col.prop(cloth, "target_volume")
+
+        col = flow.column()
+        col.prop(cloth, "pressure_factor", text="Factor")
+
+
 class PHYSICS_PT_cloth_cache(PhysicButtonsPanel, Panel):
     bl_label = "Cache"
     bl_parent_id = 'PHYSICS_PT_cloth'
@@ -382,6 +418,7 @@ classes = (
     PHYSICS_PT_cloth_physical_properties,
     PHYSICS_PT_cloth_stiffness,
     PHYSICS_PT_cloth_damping,
+    PHYSICS_PT_cloth_pressure,
     PHYSICS_PT_cloth_cache,
     PHYSICS_PT_cloth_shape,
     PHYSICS_PT_cloth_collision,

source/blender/blenkernel/BKE_cloth.h

@@ -87,7 +87,8 @@ typedef struct Cloth {
   struct MVertTri *tri;
   struct Implicit_Data *implicit; /* our implicit solver connects to this pointer */
   struct EdgeSet *edgeset;        /* used for selfcollisions */
-  int last_frame, pad4;
+  int last_frame;
+  float initial_mesh_volume; /* Initial volume of the mesh. Used for pressure */
 } Cloth;
 
 /**
@@ -192,6 +193,10 @@ typedef enum {
   CLOTH_SIMSETTINGS_FLAG_GOAL = (1 << 3),
   /** True if tearing is enabled. */
   CLOTH_SIMSETTINGS_FLAG_TEARING = (1 << 4),
+  /** True if pressure sim is enabled. */
+  CLOTH_SIMSETTINGS_FLAG_PRESSURE = (1 << 5),
+  /** Use the user defined target volume. */
+  CLOTH_SIMSETTINGS_FLAG_PRESSURE_VOL = (1 << 6),
   /** DEPRECATED, for versioning only. */
   CLOTH_SIMSETTINGS_FLAG_SCALING = (1 << 8),
   /** Edit cache in edit-mode. */

source/blender/blenkernel/intern/cloth.c

@@ -130,6 +130,11 @@ void cloth_init(ClothModifierData *clmd)
   clmd->sim_parms->eff_force_scale = 1000.0;
   clmd->sim_parms->eff_wind_scale = 250.0;
 
+  /* Pressure settings */
+  clmd->sim_parms->uniform_pressure_force = 0.0f;
+  clmd->sim_parms->target_volume = 0.0f;
+  clmd->sim_parms->pressure_factor = 1.0f;
+
   // also from softbodies
   clmd->sim_parms->maxgoal = 1.0f;
   clmd->sim_parms->mingoal = 0.0f;
@@ -291,6 +296,12 @@ static int do_init_cloth(Object *ob, ClothModifierData *clmd, Mesh *result, int
 
     BKE_cloth_solver_set_positions(clmd);
 
+    ClothSimSettings *parms = clmd->sim_parms;
+    if (parms->flags & CLOTH_SIMSETTINGS_FLAG_PRESSURE &&
+        !(parms->flags & CLOTH_SIMSETTINGS_FLAG_PRESSURE_VOL)) {
+      BKE_cloth_solver_set_volume(clmd);
+    }
+
     clmd->clothObject->last_frame = MINFRAME - 1;
     clmd->sim_parms->dt = 1.0f / clmd->sim_parms->stepsPerFrame;
   }
@@ -1742,6 +1753,6 @@ static int cloth_build_springs(ClothModifierData *clmd, Mesh *mesh)
   return 1;
 
 } /* cloth_build_springs */
-/***************************************************************************************
- * SPRING NETWORK GPU_BATCH_BUILDING IMPLEMENTATION END
- ***************************************************************************************/
+  /***************************************************************************************
+   * SPRING NETWORK GPU_BATCH_BUILDING IMPLEMENTATION END
+   ***************************************************************************************/

source/blender/blenkernel/intern/mesh_evaluate.c

@@ -2392,9 +2392,7 @@ static float mesh_calc_poly_volume_centroid(const MPoly *mpoly,
 
     /* Calculate the 6x volume of the tetrahedron formed by the 3 vertices
      * of the triangle and the origin as the fourth vertex */
-    float v_cross[3];
-    cross_v3_v3v3(v_cross, v_pivot, v_step1);
-    const float tetra_volume = dot_v3v3(v_cross, v_step2);
+    const float tetra_volume = volume_tri_tetrahedron_signed_v3_6x(v_pivot, v_step1, v_step2);
     total_volume += tetra_volume;
 
     /* Calculate the centroid of the tetrahedron formed by the 3 vertices

source/blender/blenlib/BLI_math_geom.h

@@ -92,6 +92,9 @@ float volume_tetrahedron_signed_v3(const float v1[3],
                                    const float v3[3],
                                    const float v4[3]);
 
+float volume_tri_tetrahedron_signed_v3_6x(const float v1[3], const float v2[3], const float v3[3]);
+float volume_tri_tetrahedron_signed_v3(const float v1[3], const float v2[3], const float v3[3]);
+
 bool is_edge_convex_v3(const float v1[3], const float v2[3], const float v3[3], const float v4[3]);
 bool is_quad_convex_v3(const float v1[3], const float v2[3], const float v3[3], const float v4[3]);
 bool is_quad_convex_v2(const float v1[2], const float v2[2], const float v3[2], const float v4[2]);

source/blender/blenlib/intern/math_geom.c

@@ -300,6 +300,25 @@ float volume_tetrahedron_signed_v3(const float v1[3],
   return determinant_m3_array(m) / 6.0f;
 }
 
+/**
+ * The volume from a triangle that is made into a tetrahedron.
+ * This uses a simplified formula where the tip of the tetrahedron is in the world origin.
+ * Using this method, the total volume of a closed triangle mesh can be calculated.
+ * Note that you need to divide the result by 6 to get the actual volume.
+ */
+float volume_tri_tetrahedron_signed_v3_6x(const float v1[3], const float v2[3], const float v3[3])
+{
+  float v_cross[3];
+  cross_v3_v3v3(v_cross, v1, v2);
+  float tetra_volume = dot_v3v3(v_cross, v3);
+  return tetra_volume;
+}
+
+float volume_tri_tetrahedron_signed_v3(const float v1[3], const float v2[3], const float v3[3])
+{
+  return volume_tri_tetrahedron_signed_v3_6x(v1, v2, v3) / 6.0f;
+}
+
 /********************************* Distance **********************************/
 
 /* distance p to line v1-v2

source/blender/blenloader/intern/versioning_280.c

@@ -3977,5 +3977,15 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
         br->pose_smooth_iterations = 4;
       }
     }
+    /* Cloth pressure */
+    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_Cloth) {
+          ClothModifierData *clmd = (ClothModifierData *)md;
+
+          clmd->sim_parms->pressure_factor = 1;
+        }
+      }
+    }
   }
 }

source/blender/editors/uvedit/uvedit_parametrizer.c

@@ -2048,14 +2048,13 @@ static float p_collapse_cost(PEdge *edge, PEdge *pair)
     float *co2 = e->next->next->vert->co;
 
     if ((e->face != oldf1) && (e->face != oldf2)) {
-      float tetrav2[3], tetrav3[3], c[3];
+      float tetrav2[3], tetrav3[3];
 
       /* tetrahedron volume = (1/3!)*|a.(b x c)| */
       sub_v3_v3v3(tetrav2, co1, oldv->co);
       sub_v3_v3v3(tetrav3, co2, oldv->co);
-      cross_v3_v3v3(c, tetrav2, tetrav3);
+      volumecost += fabsf(volume_tri_tetrahedron_signed_v3(tetrav2, tetrav3, edgevec));
 
-      volumecost += fabsf(dot_v3v3(edgevec, c) / 6.0f);
 #  if 0
       shapecost += dot_v3v3(co1, keepv->co);
 

source/blender/makesdna/DNA_cloth_types.h

@@ -98,6 +98,17 @@ typedef struct ClothSimSettings {
   /** Max amount to shrink cloth by 0.0f (no shrink) - 1.0f (shrink to nothing). */
   float shrink_max;
 
+  /* Air pressure */
+  /* The uniform pressure that is constanty applied to the mesh. Can be negative */
+  float uniform_pressure_force;
+  /* User set volume. This is the volume the mesh wants to expand to (the equilibrium volume). */
+  float target_volume;
+  /* The scaling factor to apply to the actual pressure.
+     pressure=( (current_volume/target_volume) - 1 + uniform_pressure_force) *
+     pressure_factor */
+  float pressure_factor;
+  char _pad7[4];
+
   /* XXX various hair stuff
    * should really be separate, this struct is a horrible mess already
    */

source/blender/makesrna/intern/rna_cloth.c

@@ -774,6 +774,46 @@ static void rna_def_cloth_sim_settings(BlenderRNA *brna)
   RNA_def_property_update(prop, 0, "rna_cloth_update");
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
 
+  /* Pressure */
+
+  prop = RNA_def_property(srna, "use_pressure", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flags", CLOTH_SIMSETTINGS_FLAG_PRESSURE);
+  RNA_def_property_ui_text(prop, "Use Pressure", "Simulate pressure inside a closed cloth mesh");
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_update(prop, 0, "rna_cloth_update");
+
+  prop = RNA_def_property(srna, "use_pressure_volume", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flags", CLOTH_SIMSETTINGS_FLAG_PRESSURE_VOL);
+  RNA_def_property_ui_text(
+      prop, "Use Custom Volume", "Use the Volume parameter as the initial volume");
+  RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
+  RNA_def_property_update(prop, 0, "rna_cloth_update");
+
+  prop = RNA_def_property(srna, "uniform_pressure_force", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_float_sdna(prop, NULL, "uniform_pressure_force");
+  RNA_def_property_range(prop, -10000.0f, 10000.0f);
+  RNA_def_property_float_default(prop, 0.0f);
+  RNA_def_property_ui_text(
+      prop,
+      "Pressure",
+      "The uniform pressure that is constanty applied to the mesh. Can be negative");
+  RNA_def_property_update(prop, 0, "rna_cloth_update");
+
+  prop = RNA_def_property(srna, "target_volume", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_float_sdna(prop, NULL, "target_volume");
+  RNA_def_property_range(prop, 0.0f, 10000.0f);
+  RNA_def_property_float_default(prop, 0.0f);
+  RNA_def_property_ui_text(
+      prop, "Target Volume", "The mesh volume where the inner/outer pressure will be the same");
+  RNA_def_property_update(prop, 0, "rna_cloth_update");
+
+  prop = RNA_def_property(srna, "pressure_factor", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_float_sdna(prop, NULL, "pressure_factor");
+  RNA_def_property_range(prop, 0.0f, 10000.0f);
+  RNA_def_property_float_default(prop, 1.0f);
+  RNA_def_property_ui_text(prop, "Pressure Scale", "Air pressure scaling factor");
+  RNA_def_property_update(prop, 0, "rna_cloth_update");
+
   /* unused */
 
   /* unused still */

source/blender/physics/BPH_mass_spring.h

@@ -53,6 +53,7 @@ int BPH_cloth_solve(struct Depsgraph *depsgraph,
                     struct ClothModifierData *clmd,
                     struct ListBase *effectors);
 void BKE_cloth_solver_set_positions(struct ClothModifierData *clmd);
+void BKE_cloth_solver_set_volume(ClothModifierData *clmd);
 
 #ifdef __cplusplus
 }

source/blender/physics/intern/BPH_mass_spring.cpp

@@ -74,6 +74,25 @@ static int cloth_count_nondiag_blocks(Cloth *cloth)
   return nondiag;
 }
 
+static float cloth_calc_volume(ClothModifierData *clmd)
+{
+  /* calc 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]);
+  }
+
+  /* We need to divide by 6 to get the actual volume */
+  vol = vol / 6.0f;
+
+  return vol;
+}
+
 int BPH_cloth_solver_init(Object *UNUSED(ob), ClothModifierData *clmd)
 {
   Cloth *cloth = clmd->clothObject;
@@ -127,6 +146,13 @@ void BKE_cloth_solver_set_positions(ClothModifierData *clmd)
   }
 }
 
+void BKE_cloth_solver_set_volume(ClothModifierData *clmd)
+{
+  Cloth *cloth = clmd->clothObject;
+
+  cloth->initial_mesh_volume = cloth_calc_volume(clmd);
+}
+
 static bool collision_response(ClothModifierData *clmd,
                                CollisionModifierData *collmd,
                                CollPair *collpair,
@@ -526,6 +552,7 @@ static void cloth_calc_force(
 {
   /* Collect forces and derivatives:  F, dFdX, dFdV */
   Cloth *cloth = clmd->clothObject;
+  ClothSimSettings *parms = clmd->sim_parms;
   Implicit_Data *data = cloth->implicit;
   unsigned int i = 0;
   float drag = clmd->sim_parms->Cvi * 0.01f; /* viscosity of air scaled in percent */
@@ -570,6 +597,48 @@ static void cloth_calc_force(
 #ifdef CLOTH_FORCE_DRAG
   BPH_mass_spring_force_drag(data, drag);
 #endif
+  /* handle pressure forces */
+  if (parms->flags & CLOTH_SIMSETTINGS_FLAG_PRESSURE) {
+    /* The difference in pressure between the inside and outside of the mesh.*/
+    float pressure_difference = 0.0f;
+
+    float init_vol;
+    if (parms->flags & CLOTH_SIMSETTINGS_FLAG_PRESSURE_VOL) {
+      init_vol = clmd->sim_parms->target_volume;
+    }
+    else {
+      init_vol = cloth->initial_mesh_volume;
+    }
+
+    /* Check if we need to calculate the volume of the mesh. */
+    if (init_vol > 1E-6f) {
+      float f;
+      float vol = cloth_calc_volume(clmd);
+
+      /* Calculate an artifical maximum value for cloth pressure. */
+      f = fabs(clmd->sim_parms->uniform_pressure_force) + 200.0f;
+
+      /* Clamp the cloth pressure to the calculated maximum value. */
+      if (vol * f < init_vol) {
+        pressure_difference = f;
+      }
+      else {
+        /* If the volume is the same don't apply any pressure. */
+        pressure_difference = (init_vol / vol) - 1;
+      }
+    }
+    pressure_difference += clmd->sim_parms->uniform_pressure_force;
+
+    pressure_difference *= clmd->sim_parms->pressure_factor;
+
+    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);
+      }
+    }
+  }
 
   /* handle external forces like wind */
   if (effectors) {

source/blender/physics/intern/implicit.h

@@ -182,6 +182,11 @@ bool BPH_mass_spring_force_spring_goal(struct Implicit_Data *data,
                                        float stiffness,
                                        float damping);
 
+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);
+
 /* ======== Hair Volumetric Forces ======== */
 
 struct HairGrid;

source/blender/physics/intern/implicit_blender.c

@@ -1469,6 +1469,7 @@ void BPH_mass_spring_force_face_wind(
 
   /* calculate face normal and area */
   area = calc_nor_area_tri(nor, data->X[v1], data->X[v2], data->X[v3]);
+  /* The force is calculated and split up evenly for each of the three face verts */
   factor = effector_scale * area / 3.0f;
 
   world_to_root_v3(data, v1, win, winvec[v1]);
@@ -1481,6 +1482,29 @@ void BPH_mass_spring_force_face_wind(
   madd_v3_v3fl(data->F[v3], nor, factor * dot_v3v3(win, nor));
 }
 
+float BPH_tri_tetra_volume_signed_6x(Implicit_Data *data, int v1, int v2, int v3)
+{
+  /* The result will be 6x the volume */
+  return volume_tri_tetrahedron_signed_v3_6x(data->X[v1], data->X[v2], data->X[v3]);
+}
+
+void BPH_mass_spring_force_pressure(
+    Implicit_Data *data, int v1, int v2, int v3, float pressure_difference)
+{
+  float nor[3], area;
+  float factor;
+
+  /* calculate face normal and area */
+  area = calc_nor_area_tri(nor, data->X[v1], data->X[v2], data->X[v3]);
+  /* The force is calculated and split up evenly for each of the three face verts */
+  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);
+}
+
 static void edge_wind_vertex(const float dir[3],
                              float length,
                              float radius,