Commit: 7a53563c9829d73253478c3efe6a8b0523fe1ad8
Author: Lukas Tönne
Date: Thu Nov 13 16:06:39 2014 +0100
Branches: hair_immediate_fixes
https://developer.blender.org/rB7a53563c9829d73253478c3efe6a8b0523fe1ad8
Implementation of a target density feature for the hair simulation.
This allows setting a target density which the fluid simulation will
take into account as an additional term in the pressure Poisson
equation. Based on two papers
"Detail Preserving Continuum Simulation of Straight Hair" (McAdams et al. 2009)
and
"Two-way Coupled SPH and Particle Level Set Fluid Simulation" (Losasso et al.
2008)
Currently the target pressure is specified directly, but it will be
a lot more convenient to define this in terms of a geometric value such
as "number of hairs per area" (combined with hair "thickness").
===================================================================
M release/scripts/startup/bl_ui/properties_particle.py
M source/blender/makesdna/DNA_cloth_types.h
M source/blender/makesrna/intern/rna_cloth.c
M source/blender/physics/intern/BPH_mass_spring.cpp
M source/blender/physics/intern/hair_volume.cpp
M source/blender/physics/intern/implicit.h
===================================================================
diff --git a/release/scripts/startup/bl_ui/properties_particle.py
b/release/scripts/startup/bl_ui/properties_particle.py
index f8d1612..7e42ad9 100644
--- a/release/scripts/startup/bl_ui/properties_particle.py
+++ b/release/scripts/startup/bl_ui/properties_particle.py
@@ -304,10 +304,9 @@ class PARTICLE_PT_hair_dynamics(ParticleButtonsPanel,
Panel):
col.label(text="Volume")
col.prop(cloth, "air_damping", text="Air Drag")
col.prop(cloth, "internal_friction", slider=True)
- sub = col.row(align=True)
- # XXX disabled due to stability issues
- #sub.prop(cloth, "pressure", slider=True, text="Pressure")
- #sub.prop(cloth, "pressure_threshold", slider=True, text="Threshold")
+ sub = col.column(align=True)
+ sub.prop(cloth, "density_target", text="Density Target")
+ sub.prop(cloth, "density_strength", slider=True, text="Strength")
col.prop(cloth, "voxel_cell_size")
split.separator()
diff --git a/source/blender/makesdna/DNA_cloth_types.h
b/source/blender/makesdna/DNA_cloth_types.h
index f4d8faa..3144dad 100644
--- a/source/blender/makesdna/DNA_cloth_types.h
+++ b/source/blender/makesdna/DNA_cloth_types.h
@@ -69,8 +69,8 @@ typedef struct ClothSimSettings {
float goalspring;
float goalfrict;
float velocity_smooth; /* smoothing of velocities for hair */
- float pressure; /* pressure factor from hair
density */
- float pressure_threshold; /* minimum density for hair pressure */
+ float density_target; /* minimum density for hair */
+ float density_strength; /* influence of hair density */
float collider_friction; /* friction with colliders */
float vel_damping; /* damp the velocity to speed up getting to the
resting position */
float shrink_min; /* min amount to shrink cloth by 0.0f (no shrink)
- 1.0f (shrink to nothing) */
diff --git a/source/blender/makesrna/intern/rna_cloth.c
b/source/blender/makesrna/intern/rna_cloth.c
index 1176da7..c312870 100644
--- a/source/blender/makesrna/intern/rna_cloth.c
+++ b/source/blender/makesrna/intern/rna_cloth.c
@@ -385,16 +385,16 @@ static void rna_def_cloth_sim_settings(BlenderRNA *brna)
RNA_def_property_ui_text(prop, "Collider Friction", "");
RNA_def_property_update(prop, 0, "rna_cloth_update");
- prop = RNA_def_property(srna, "pressure", PROP_FLOAT, PROP_NONE);
- RNA_def_property_float_sdna(prop, NULL, "pressure");
- RNA_def_property_range(prop, 0.0f, 1000.0f);
- RNA_def_property_ui_text(prop, "Internal Pressure", "Generate outward
force based on hair density");
+ prop = RNA_def_property(srna, "density_target", PROP_FLOAT, PROP_NONE);
+ RNA_def_property_float_sdna(prop, NULL, "density_target");
+ RNA_def_property_range(prop, 0.0f, 1000000.0f);
+ RNA_def_property_ui_text(prop, "Target Density", "Maximum density of
hair");
RNA_def_property_update(prop, 0, "rna_cloth_update");
- prop = RNA_def_property(srna, "pressure_threshold", PROP_FLOAT,
PROP_NONE);
- RNA_def_property_float_sdna(prop, NULL, "pressure_threshold");
+ prop = RNA_def_property(srna, "density_strength", PROP_FLOAT,
PROP_NONE);
+ RNA_def_property_float_sdna(prop, NULL, "density_strength");
RNA_def_property_range(prop, 0.0f, 1000.0f);
- RNA_def_property_ui_text(prop, "Internal Pressure Threshold", "No
pressure force is generated below this pressure value");
+ RNA_def_property_ui_text(prop, "Target Density Strength", "Influence of
target density on the simulation");
RNA_def_property_update(prop, 0, "rna_cloth_update");
/* mass */
diff --git a/source/blender/physics/intern/BPH_mass_spring.cpp
b/source/blender/physics/intern/BPH_mass_spring.cpp
index ee58dca..baac772 100644
--- a/source/blender/physics/intern/BPH_mass_spring.cpp
+++ b/source/blender/physics/intern/BPH_mass_spring.cpp
@@ -875,8 +875,8 @@ static void cloth_continuum_step(ClothModifierData *clmd,
float dt)
const float fluid_factor = 0.95f; /* blend between PIC and FLIP methods
*/
float smoothfac = parms->velocity_smooth;
- float pressfac = parms->pressure;
- float minpress = parms->pressure_threshold;
+ float denstarget = parms->density_target;
+ float densfac = parms->density_strength;
float gmin[3], gmax[3];
int i;
@@ -888,14 +888,15 @@ static void cloth_continuum_step(ClothModifierData *clmd,
float dt)
hair_get_boundbox(clmd, gmin, gmax);
/* gather velocities & density */
- if (smoothfac > 0.0f || pressfac > 0.0f) {
+ if (smoothfac > 0.0f || densfac > 0.0f) {
HairGrid *grid =
BPH_hair_volume_create_vertex_grid(clmd->sim_parms->voxel_cell_size, gmin,
gmax);
BPH_hair_volume_set_debug_data(grid, clmd->debug_data);
+// BPH_hair_volume_set_debug_value(grid, (int)(spring2->ij ==
clmd->sim_parms->density_target));
cloth_continuum_fill_grid(grid, cloth);
/* main hair continuum solver */
- BPH_hair_volume_solve_divergence(grid, dt);
+ BPH_hair_volume_solve_divergence(grid, dt, denstarget, densfac);
for (i = 0, vert = cloth->verts; i < numverts; i++, vert++) {
float x[3], v[3], nv[3];
diff --git a/source/blender/physics/intern/hair_volume.cpp
b/source/blender/physics/intern/hair_volume.cpp
index 5dadd45..4d10c04 100644
--- a/source/blender/physics/intern/hair_volume.cpp
+++ b/source/blender/physics/intern/hair_volume.cpp
@@ -530,10 +530,22 @@ void BPH_hair_volume_normalize_vertex_grid(HairGrid *grid)
}
}
-bool BPH_hair_volume_solve_divergence(HairGrid *grid, float dt)
+static const float density_threshold = 0.001f; /* cells with density below
this are considered empty */
+
+/* Contribution of target density pressure to the laplacian in the pressure
poisson equation.
+ * This is based on the model found in
+ * "Two-way Coupled SPH and Particle Level Set Fluid Simulation" (Losasso et
al., 2008)
+ */
+BLI_INLINE float hair_volume_density_divergence(float density, float
target_density, float strength)
+{
+ if (density > density_threshold && density > target_density)
+ return strength * density * logf(target_density / density);
+ else
+ return 0.0f;
+}
+
+bool BPH_hair_volume_solve_divergence(HairGrid *grid, float dt, float
target_density, float target_strength)
{
- const float density_threshold = 0.001f; /* cells with density below
this are considered empty */
-
const float flowfac = grid->cellsize / dt;
const float inv_flowfac = dt / grid->cellsize;
@@ -576,12 +588,17 @@ bool BPH_hair_volume_solve_divergence(HairGrid *grid,
float dt)
float dy = vert_py->velocity[1] - v[1];
float dz = vert_pz->velocity[2] - v[2];
+ float divergence = (dx + dy + dz) * flowfac;
+
+ /* adjustment term for target density */
+ float target =
hair_volume_density_divergence(vert->density, target_density, target_strength);
+
/* B vector contains the finite difference
approximation of the velocity divergence.
* Note: according to the discretized
Navier-Stokes equation the rhs vector
* and resulting pressure gradient should be
multiplied by the (inverse) density;
* however, this is already included in the
weighting of hair velocities on the grid!
*/
- B[u] = (dx + dy + dz) * flowfac;
+ B[u] = divergence + target;
}
}
}
diff --git a/source/blender/physics/intern/implicit.h
b/source/blender/physics/intern/implicit.h
index 203e6f3..246b916 100644
--- a/source/blender/physics/intern/implicit.h
+++ b/source/blender/physics/intern/implicit.h
@@ -187,7 +187,7 @@ void BPH_hair_volume_add_segment(struct HairGrid *grid,
void BPH_hair_volume_normalize_vertex_grid(struct HairGrid *grid);
-bool BPH_hair_volume_solve_divergence(struct HairGrid *grid, float dt);
+bool BPH_hair_volume_solve_divergence(struct HairGrid *grid, float dt, float
target_density, float target_strength);
#if 0 /* XXX weighting is incorrect, disabled for now */
void BPH_hair_volume_vertex_grid_filter_box(struct HairVertexGrid *grid, int
kernel_size);
#endif
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