Fluid: Added obstacle fluid distance parameter

Being able to adjust the distance between fluid and obstacles comes in handy when trying to achieve a fluid motion over inclined obstacles.

Depending on the slope of such obstacles, already small adjustments of this value can help when particles stick to obstacle surfaces (i.e. make particles not stick to obstacles).

intern/mantaflow/intern/MANTA_main.cpp

@@ -845,6 +845,7 @@ void MANTA::initializeRNAMap(FluidModifierData *fmd)
   mRNAMap["PARTICLE_MAXIMUM"] = to_string(fds->particle_maximum);
   mRNAMap["PARTICLE_RADIUS"] = to_string(fds->particle_radius);
   mRNAMap["FRACTIONS_THRESHOLD"] = to_string(fds->fractions_threshold);
+  mRNAMap["FRACTIONS_DISTANCE"] = to_string(fds->fractions_distance);
   mRNAMap["MESH_CONCAVE_UPPER"] = to_string(fds->mesh_concave_upper);
   mRNAMap["MESH_CONCAVE_LOWER"] = to_string(fds->mesh_concave_lower);
   mRNAMap["MESH_PARTICLE_RADIUS"] = to_string(fds->mesh_particle_radius);

intern/mantaflow/intern/strings/liquid_script.h

@@ -41,6 +41,7 @@ using_mesh_s$ID$       = $USING_MESH$\n\
 using_final_mesh_s$ID$ = $USING_IMPROVED_MESH$\n\
 using_fractions_s$ID$  = $USING_FRACTIONS$\n\
 fracThreshold_s$ID$    = $FRACTIONS_THRESHOLD$\n\
+fracDistance_s$ID$     = $FRACTIONS_DISTANCE$\n\
 flipRatio_s$ID$        = $FLIP_RATIO$\n\
 concaveUpper_s$ID$     = $MESH_CONCAVE_UPPER$\n\
 concaveLower_s$ID$     = $MESH_CONCAVE_LOWER$\n\
@@ -243,6 +244,8 @@ def liquid_step_$ID$():\n\
     pp_s$ID$.advectInGrid(flags=flags_s$ID$, vel=vel_s$ID$, integrationMode=IntRK4, deleteInObstacle=deleteInObstacle_s$ID$, stopInObstacle=False, skipNew=True)\n\
     \n\
     mantaMsg('Pushing particles out of obstacles')\n\
+    if using_obstacle_s$ID$:\n\
+        pushOutofObs(parts=pp_s$ID$, flags=flags_s$ID$, phiObs=phiObsIn_s$ID$, thresh=fracDistance_s$ID$)\n\
     pushOutofObs(parts=pp_s$ID$, flags=flags_s$ID$, phiObs=phiObs_s$ID$)\n\
     \n\
     # save original states for later (used during mesh / secondary particle creation)\n\

release/scripts/startup/bl_ui/properties_physics_fluid.py

@@ -507,7 +507,8 @@ class PHYSICS_PT_liquid(PhysicButtonsPanel, Panel):
         col.prop(domain, "use_fractions", text="Fractional Obstacles")
         sub = col.column()
         sub.active = domain.use_fractions
-        sub.prop(domain, "fractions_threshold", text="Obstacle-Fluid Threshold")
+        sub.prop(domain, "fractions_distance", text="Obstacle Distance")
+        sub.prop(domain, "fractions_threshold", text="Threshold")
 
 
 class PHYSICS_PT_flow_source(PhysicButtonsPanel, Panel):

source/blender/blenkernel/intern/fluid.c

@@ -4985,6 +4985,7 @@ void BKE_fluid_modifier_copy(const struct FluidModifierData *fmd,
     tfds->particle_radius = fds->particle_radius;
     tfds->particle_band_width = fds->particle_band_width;
     tfds->fractions_threshold = fds->fractions_threshold;
+    tfds->fractions_distance = fds->fractions_distance;
     tfds->sys_particle_maximum = fds->sys_particle_maximum;
 
     /* diffusion options*/

source/blender/blenloader/intern/versioning_290.c

@@ -912,4 +912,17 @@ void blo_do_versions_290(FileData *fd, Library *UNUSED(lib), Main *bmain)
       }
     }
   }
+
+  if (!DNA_struct_elem_find(fd->filesdna, "FluidModifierData", "float", "fractions_distance")) {
+    LISTBASE_FOREACH (Object *, ob, &bmain->objects) {
+      LISTBASE_FOREACH (ModifierData *, md, &ob->modifiers) {
+        if (md->type == eModifierType_Fluid) {
+          FluidModifierData *fmd = (FluidModifierData *)md;
+          if (fmd->domain) {
+            fmd->domain->fractions_distance = 0.5;
+          }
+        }
+      }
+    }
+  }
 }

source/blender/makesdna/DNA_fluid_defaults.h

@@ -109,6 +109,7 @@
     .particle_radius = 1.0f, \
     .particle_band_width = 3.0f, \
     .fractions_threshold = 0.05f, \
+    .fractions_distance = 0.5f, \
     .flip_ratio = 0.97f, \
     .sys_particle_maximum = 0, \
     .simulation_method = FLUID_DOMAIN_METHOD_FLIP, \

source/blender/makesdna/DNA_fluid_types.h

@@ -586,10 +586,11 @@ typedef struct FluidDomainSettings {
   float particle_radius;
   float particle_band_width;
   float fractions_threshold;
+  float fractions_distance;
   float flip_ratio;
   int sys_particle_maximum;
   short simulation_method;
-  char _pad4[2];
+  char _pad4[6];
 
   /* Diffusion options. */
   float surface_tension;

source/blender/makesrna/intern/rna_fluid.c

@@ -1895,12 +1895,22 @@ static void rna_def_fluid_domain_settings(BlenderRNA *brna)
   RNA_def_property_range(prop, 0.001, 1.0);
   RNA_def_property_ui_range(prop, 0.01, 1.0, 0.05, -1);
   RNA_def_property_ui_text(prop,
-                           "Obstacle-Fluid Threshold",
+                           "Obstacle Threshold",
                            "Determines how much fluid is allowed in an obstacle cell "
                            "(higher values will tag a boundary cell as an obstacle easier "
                            "and reduce the boundary smoothening effect)");
   RNA_def_property_update(prop, NC_OBJECT | ND_MODIFIER, "rna_Fluid_datacache_reset");
 
+  prop = RNA_def_property(srna, "fractions_distance", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_range(prop, -5.0, 5.0);
+  RNA_def_property_ui_range(prop, 0.01, 5.0, 0.1, -1);
+  RNA_def_property_ui_text(prop,
+                           "Obstacle Distance",
+                           "Determines how far apart fluid and obstacle are (higher values will "
+                           "result in fluid being further away from obstacles, smaller values "
+                           "will let fluid move towards the inside of obstacles)");
+  RNA_def_property_update(prop, NC_OBJECT | ND_MODIFIER, "rna_Fluid_datacache_reset");
+
   prop = RNA_def_property(srna, "sys_particle_maximum", PROP_INT, PROP_NONE);
   RNA_def_property_int_sdna(prop, NULL, "sys_particle_maximum");
   RNA_def_property_range(prop, 0, INT_MAX);