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Corrected the divergence and gradient calculation for the hair grid 

solver input and output.

This uses the central difference method (instead of combined forward/
backward difference), which makes it easier to correctly account for
grid borders.
This commit is contained in:
Lukas Tönne 2014-11-14 14:41:55 +01:00
parent 42fc88de43
commit 7c153c3a3d
1 changed files with 36 additions and 23 deletions
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59
source/blender/physics/intern/hair_volume.cpp
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@ -310,6 +310,13 @@ BLI_INLINE int hair_grid_weights(const int res[3], const float gmin[3], float sc
return offset;
}
BLI_INLINE void grid_to_world(HairGrid *grid, float vecw[3], const float vec[3])
{
copy_v3_v3(vecw, vec);
mul_v3_fl(vecw, grid->cellsize);
add_v3_v3(vecw, grid->gmin);
}
void BPH_hair_volume_add_vertex(HairGrid *grid, const float x[3], const float v[3])
{
const int res[3] = { grid->res[0], grid->res[1], grid->res[2] };
@ -364,13 +371,6 @@ BLI_INLINE int major_axis_v3(const float v[3])
return a > b ? (a > c ? 0 : 2) : (b > c ? 1 : 2);
}
BLI_INLINE void grid_to_world(HairGrid *grid, float vecw[3], const float vec[3])
{
copy_v3_v3(vecw, vec);
mul_v3_fl(vecw, grid->cellsize);
add_v3_v3(vecw, grid->gmin);
}
void BPH_hair_volume_set_debug_value(HairGrid *grid, int debug_value)
{
grid->debug_value = debug_value;
@ -609,8 +609,8 @@ BLI_INLINE float hair_volume_density_divergence(float density, float target_dens
bool BPH_hair_volume_solve_divergence(HairGrid *grid, float dt, float target_density, float target_strength)
{
const float flowfac = grid->cellsize / dt;
const float inv_flowfac = dt / grid->cellsize;
const float flowfac = grid->cellsize;
const float inv_flowfac = 1.0f / grid->cellsize;
/*const int num_cells = hair_grid_size(grid->res);*/
const int res[3] = { grid->res[0], grid->res[1], grid->res[2] };
@ -660,16 +660,23 @@ bool BPH_hair_volume_solve_divergence(HairGrid *grid, float dt, float target_den
}
vert = vert_start + i * stride0 + j * stride1 + k * stride2;
HairGridVert *vert_px = vert + stride0;
HairGridVert *vert_py = vert + stride1;
HairGridVert *vert_pz = vert + stride2;
const float *v = vert->velocity;
float dx = NEIGHBOR_MARGIN_i1 ? 0.0f : vert_px->velocity[0] - v[0];
float dy = NEIGHBOR_MARGIN_j1 ? 0.0f : vert_py->velocity[1] - v[1];
float dz = NEIGHBOR_MARGIN_k1 ? 0.0f : vert_pz->velocity[2] - v[2];
const float *v0 = vert->velocity;
float dx = 0.0f, dy = 0.0f, dz = 0.0f;
if (!NEIGHBOR_MARGIN_i0)
dx += v0[0] - (vert - stride0)->velocity[0];
if (!NEIGHBOR_MARGIN_i1)
dx += (vert + stride0)->velocity[0] - v0[0];
if (!NEIGHBOR_MARGIN_j0)
dy += v0[1] - (vert - stride1)->velocity[1];
if (!NEIGHBOR_MARGIN_j1)
dy += (vert + stride1)->velocity[1] - v0[1];
if (!NEIGHBOR_MARGIN_k0)
dz += v0[2] - (vert - stride2)->velocity[2];
if (!NEIGHBOR_MARGIN_k1)
dz += (vert + stride2)->velocity[2] - v0[2];
float divergence = (dx + dy + dz) * flowfac;
float divergence = -0.5f * flowfac * (dx + dy + dz);
/* adjustment term for target density */
float target = hair_volume_density_divergence(vert->density, target_density, target_strength);
@ -766,16 +773,22 @@ bool BPH_hair_volume_solve_divergence(HairGrid *grid, float dt, float target_den
vert = vert_start + i * stride0 + j * stride1 + k * stride2;
if (vert->density > density_threshold) {
float p0 = p[u];
float p_left = p[u - stride0];
float p_right = p[u + stride0];
float p_down = p[u - stride1];
float p_up = p[u + stride1];
float p_bottom = p[u - stride2];
float p_top = p[u + stride2];
/* finite difference estimate of pressure gradient */
float grad_p[3];
grad_p[0] = p0 - p[u - stride0];
grad_p[1] = p0 - p[u - stride1];
grad_p[2] = p0 - p[u - stride2];
float dvel[3];
dvel[0] = p_right - p_left;
dvel[1] = p_up - p_down;
dvel[2] = p_top - p_bottom;
mul_v3_fl(dvel, -0.5f * inv_flowfac);
/* pressure gradient describes velocity delta */
madd_v3_v3v3fl(vert->velocity_smooth, vert->velocity, grad_p, inv_flowfac);
add_v3_v3v3(vert->velocity_smooth, vert->velocity, dvel);
}
else {
zero_v3(vert->velocity_smooth);