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/*
* Copyright 2011-2020 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
CCL_NAMESPACE_BEGIN
/* Area light sampling */
/* Uses the following paper:
*
* Carlos Urena et al.
* An Area-Preserving Parametrization for Spherical Rectangles.
*
* https://www.solidangle.com/research/egsr2013_spherical_rectangle.pdf
*
* Note: light_p is modified when sample_coord is true.
*/
ccl_device_inline float rect_light_sample(float3 P,
float3 *light_p,
float3 axisu,
float3 axisv,
float randu,
float randv,
bool sample_coord)
{
/* In our name system we're using P for the center,
* which is o in the paper.
*/
float3 corner = *light_p - axisu * 0.5f - axisv * 0.5f;
float axisu_len, axisv_len;
/* Compute local reference system R. */
float3 x = normalize_len(axisu, &axisu_len);
float3 y = normalize_len(axisv, &axisv_len);
float3 z = cross(x, y);
/* Compute rectangle coords in local reference system. */
float3 dir = corner - P;
float z0 = dot(dir, z);
/* Flip 'z' to make it point against Q. */
if (z0 > 0.0f) {
z *= -1.0f;
z0 *= -1.0f;
}
float x0 = dot(dir, x);
float y0 = dot(dir, y);
float x1 = x0 + axisu_len;
float y1 = y0 + axisv_len;
/* Compute internal angles (gamma_i). */
float4 diff = make_float4(x0, y1, x1, y0) - make_float4(x1, y0, x0, y1);
float4 nz = make_float4(y0, x1, y1, x0) * diff;
nz = nz / sqrt(z0 * z0 * diff * diff + nz * nz);
float g0 = safe_acosf(-nz.x * nz.y);
float g1 = safe_acosf(-nz.y * nz.z);
float g2 = safe_acosf(-nz.z * nz.w);
float g3 = safe_acosf(-nz.w * nz.x);
/* Compute predefined constants. */
float b0 = nz.x;
float b1 = nz.z;
float b0sq = b0 * b0;
float k = M_2PI_F - g2 - g3;
/* Compute solid angle from internal angles. */
float S = g0 + g1 - k;
if (sample_coord) {
/* Compute cu. */
float au = randu * S + k;
float fu = (cosf(au) * b0 - b1) / sinf(au);
float cu = 1.0f / sqrtf(fu * fu + b0sq) * (fu > 0.0f ? 1.0f : -1.0f);
cu = clamp(cu, -1.0f, 1.0f);
/* Compute xu. */
float xu = -(cu * z0) / max(sqrtf(1.0f - cu * cu), 1e-7f);
xu = clamp(xu, x0, x1);
/* Compute yv. */
float z0sq = z0 * z0;
float y0sq = y0 * y0;
float y1sq = y1 * y1;
float d = sqrtf(xu * xu + z0sq);
float h0 = y0 / sqrtf(d * d + y0sq);
float h1 = y1 / sqrtf(d * d + y1sq);
float hv = h0 + randv * (h1 - h0), hv2 = hv * hv;
float yv = (hv2 < 1.0f - 1e-6f) ? (hv * d) / sqrtf(1.0f - hv2) : y1;
/* Transform (xu, yv, z0) to world coords. */
*light_p = P + xu * x + yv * y + z0 * z;
}
/* return pdf */
if (S != 0.0f)
return 1.0f / S;
else
return 0.0f;
}
ccl_device_inline float3 ellipse_sample(float3 ru, float3 rv, float randu, float randv)
{
to_unit_disk(&randu, &randv);
return ru * randu + rv * randv;
}
ccl_device float3 disk_light_sample(float3 v, float randu, float randv)
{
float3 ru, rv;
make_orthonormals(v, &ru, &rv);
return ellipse_sample(ru, rv, randu, randv);
}
ccl_device float3 distant_light_sample(float3 D, float radius, float randu, float randv)
{
return normalize(D + disk_light_sample(D, randu, randv) * radius);
}
ccl_device float3
sphere_light_sample(float3 P, float3 center, float radius, float randu, float randv)
{
return disk_light_sample(normalize(P - center), randu, randv) * radius;
}
ccl_device float spot_light_attenuation(float3 dir, float spot_angle, float spot_smooth, float3 N)
{
float attenuation = dot(dir, N);
if (attenuation <= spot_angle) {
attenuation = 0.0f;
}
else {
float t = attenuation - spot_angle;
if (t < spot_smooth && spot_smooth != 0.0f)
attenuation *= smoothstepf(t / spot_smooth);
}
return attenuation;
}
ccl_device float lamp_light_pdf(KernelGlobals *kg, const float3 Ng, const float3 I, float t)
{
float cos_pi = dot(Ng, I);
if (cos_pi <= 0.0f)
return 0.0f;
return t * t / cos_pi;
}
CCL_NAMESPACE_END
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