/* For ease of use, I've also introduced a 'reflection' and 'reflection color' parameter, which isn't
* physically correct. This works as an RGB tint/gain on out-scattered light, but doesn't affect the light
* that is transmitted through the volume. While having wavelength dependent absorption/scattering is more correct,
* it also makes it harder to control the overall look of the volume since coloring the outscattered light results
* in the inverse color being transmitted through the rest of the volume.
*/
static void volumeintegrate(struct ShadeInput *shi, float *col, float *co, float *endco)
{
float radiance[3] = {0.f, 0.f, 0.f};
float tr[3] = {1.f, 1.f, 1.f};
float p[3] = {co[0], co[1], co[2]};
float step_vec[3] = {endco[0] - co[0], endco[1] - co[1], endco[2] - co[2]};
const float stepsize = shi->mat->vol.stepsize;
float t0 = 0.f;
float pt0 = t0;
float t1 = normalize_v3(step_vec); /* returns vector length */
t0 += stepsize * ((shi->mat->vol.stepsize_type == MA_VOL_STEP_CONSTANT) ? 0.5f : BLI_thread_frand(shi->thread));
p[0] += t0 * step_vec[0];
p[1] += t0 * step_vec[1];
p[2] += t0 * step_vec[2];
mul_v3_fl(step_vec, stepsize);
for (; t0 < t1; pt0 = t0, t0 += stepsize) {
const float density = vol_get_density(shi, p);
if (density > 0.00001f) {
float scatter_col[3] = {0.f, 0.f, 0.f}, emit_col[3];
const float stepd = (t0 - pt0) * density;
/* transmittance component (alpha) */
vol_get_transmittance_seg(shi, tr, stepsize, co, density);
if (t0 > t1 * 0.25f) {
/* only use depth cutoff after we've traced a little way into the volume */
if (luminance(tr) < shi->mat->vol.depth_cutoff) break;
}
vol_get_emission(shi, emit_col, p);
if (shi->obi->volume_precache) {
float p2[3];
p2[0] = p[0] + (step_vec[0] * 0.5f);
p2[1] = p[1] + (step_vec[1] * 0.5f);
p2[2] = p[2] + (step_vec[2] * 0.5f);
vol_get_precached_scattering(&R, shi, scatter_col, p2);
} else
vol_get_scattering(shi, scatter_col, p);
radiance[0] += stepd * tr[0] * (emit_col[0] + scatter_col[0]);
radiance[1] += stepd * tr[1] * (emit_col[1] + scatter_col[1]);
radiance[2] += stepd * tr[2] * (emit_col[2] + scatter_col[2]);
}
add_v3_v3(p, step_vec);
}
/* multiply original color (from behind volume) with transmittance over entire distance */
mul_v3_v3v3(col, tr, col);
add_v3_v3(col, radiance);
/* alpha <-- transmission luminance */
col[3] = 1.0f - luminance(tr);
}
/* Compute transmittance = e^(-attenuation) */
static void vol_get_transmittance(ShadeInput *shi, float tr[3], const float co[3], const float endco[3])
{
float p[3] = {co[0], co[1], co[2]};
float step_vec[3] = {endco[0] - co[0], endco[1] - co[1], endco[2] - co[2]};
float tau[3] = {0.f, 0.f, 0.f};
float t0 = 0.f;
float t1 = normalize_v3(step_vec);
float pt0 = t0;
t0 += shi->mat->vol.stepsize * ((shi->mat->vol.stepsize_type == MA_VOL_STEP_CONSTANT) ? 0.5f : BLI_thread_frand(shi->thread));
p[0] += t0 * step_vec[0];
p[1] += t0 * step_vec[1];
p[2] += t0 * step_vec[2];
mul_v3_fl(step_vec, shi->mat->vol.stepsize);
for (; t0 < t1; pt0 = t0, t0 += shi->mat->vol.stepsize) {
const float d = vol_get_density(shi, p);
const float stepd = (t0 - pt0) * d;
float sigma_t[3];
vol_get_sigma_t(shi, sigma_t, p);
tau[0] += stepd * sigma_t[0];
tau[1] += stepd * sigma_t[1];
tau[2] += stepd * sigma_t[2];
add_v3_v3(p, step_vec);
}
/* return transmittance */
tr[0] = expf(-tau[0]);
tr[1] = expf(-tau[1]);
tr[2] = expf(-tau[2]);
}
/* Traces a shadow through the object,
* pretty much gets the transmission over a ray path */
void shade_volume_shadow(struct ShadeInput *shi, struct ShadeResult *shr, struct Isect *last_is)
{
float hitco[3];
float tr[3] = {1.0,1.0,1.0};
Isect is;
float *startco, *endco;
float density=0.f;
memset(shr, 0, sizeof(ShadeResult));
/* if 1st hit normal is facing away from the camera,
* then we're inside the volume already. */
if (shi->flippednor) {
startco = last_is->start;
endco = shi->co;
}
/* trace to find a backface, the other side bounds of the volume */
/* (ray intersect ignores front faces here) */
else if (vol_get_bounds(shi, shi->co, shi->view, hitco, &is, VOL_BOUNDS_DEPTH)) {
startco = shi->co;
endco = hitco;
}
else {
shr->combined[0] = shr->combined[1] = shr->combined[2] = 0.f;
shr->alpha = shr->combined[3] = 1.f;
return;
}
density = vol_get_density(shi, startco);
vol_get_transmittance(shi, tr, startco, endco);
VecCopyf(shr->combined, tr);
shr->combined[3] = 1.0f - luminance(tr);
}
