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Perform grid-based velocity smoothing for hair outside of the implicit

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solver step.

Calculating forces and jacobians from linearly interpolated grid values
is problematic due to discontinuities at the grid boundaries. The new
approach of modifying velocities after the backward euler solver step
was suggested in a newer paper

"Detail Preserving Continuum Simulation of Straight Hair"
(McAdams, Selle 2009)

Conflicts:
	source/blender/physics/intern/BPH_mass_spring.cpp
This commit is contained in:
Lukas Tönne
2014-10-31 11:59:14 +01:00
parent 4381fa3157
commit aea309779f
5 changed files with 218 additions and 66 deletions
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24
source/blender/physics/intern/implicit.h
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@@ -111,20 +111,26 @@ BLI_INLINE int hash_collpair(int type, CollPair *collpair)
void BPH_mass_spring_solver_debug_data(struct Implicit_Data *id, struct SimDebugData *debug_data);
void BPH_mass_spring_set_vertex_mass(struct Implicit_Data *data, int index, float mass);
void BPH_mass_spring_set_rest_transform(struct Implicit_Data *data, int index, float rot[3][3]);
void BPH_mass_spring_set_motion_state(struct Implicit_Data *data, int index, const float x[3], const float v[3]);
void BPH_mass_spring_set_position(struct Implicit_Data *data, int index, const float x[3]);
void BPH_mass_spring_set_velocity(struct Implicit_Data *data, int index, const float v[3]);
void BPH_mass_spring_get_motion_state(struct Implicit_Data *data, int index, float x[3], float v[3]);
void BPH_mass_spring_set_vertex_mass(struct Implicit_Data *data, int index, float mass);
void BPH_mass_spring_get_position(struct Implicit_Data *data, int index, float x[3]);
/* modified velocity during solver step */
void BPH_mass_spring_get_new_velocity(struct Implicit_Data *data, int index, float v[3]);
void BPH_mass_spring_set_new_velocity(struct Implicit_Data *data, int index, const float v[3]);
void BPH_mass_spring_clear_constraints(struct Implicit_Data *data);
void BPH_mass_spring_add_constraint_ndof0(struct Implicit_Data *data, int index, const float dV[3]);
void BPH_mass_spring_add_constraint_ndof1(struct Implicit_Data *data, int index, const float c1[3], const float c2[3], const float dV[3]);
void BPH_mass_spring_add_constraint_ndof2(struct Implicit_Data *data, int index, const float c1[3], const float dV[3]);
bool BPH_mass_spring_solve(struct Implicit_Data *data, float dt, struct ImplicitSolverResult *result);
bool BPH_mass_spring_solve_velocities(struct Implicit_Data *data, float dt, struct ImplicitSolverResult *result);
bool BPH_mass_spring_solve_positions(struct Implicit_Data *data, float dt);
void BPH_mass_spring_apply_result(struct Implicit_Data *data);
/* Clear the force vector at the beginning of the time step */
@@ -170,6 +176,20 @@ void BPH_hair_volume_normalize_vertex_grid(struct HairVertexGrid *grid);
#if 0 /* XXX weighting is incorrect, disabled for now */
void BPH_hair_volume_vertex_grid_filter_box(struct HairVertexGrid *grid, int kernel_size);
#endif
/* Effect of fluid simulation grid on velocities.
* fluid_factor controls blending between PIC (Particle-in-Cell)
* and FLIP (Fluid-Implicit-Particle) methods (0 = only PIC, 1 = only FLIP)
*/
void BPH_hair_volume_grid_velocity(struct HairVertexGrid *grid, const float x[3], const float v[3],
float fluid_factor,
float r_v[3]);
/* XXX Warning: expressing grid effects on velocity as a force is not very stable,
* due to discontinuities in interpolated values!
* Better use hybrid approaches such as described in
* "Detail Preserving Continuum Simulation of Straight Hair"
* (McAdams, Selle 2009)
*/
void BPH_hair_volume_vertex_grid_forces(struct HairVertexGrid *grid, const float x[3], const float v[3],
float smoothfac, float pressurefac, float minpressure,
float f[3], float dfdx[3][3], float dfdv[3][3]);