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/*
* Copyright 2011-2013 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
/*
* "A Practical Analytic Model for Daylight"
* A. J. Preetham, Peter Shirley, Brian Smits
*/
__device float sky_angle_between(float thetav, float phiv, float theta, float phi)
{
float cospsi = sinf(thetav)*sinf(theta)*cosf(phi - phiv) + cosf(thetav)*cosf(theta);
return safe_acosf(cospsi);
}
__device float sky_perez_function(__constant float *lam, float theta, float gamma)
{
float ctheta = cosf(theta);
float cgamma = cosf(gamma);
return (1.0f + lam[0]*expf(lam[1]/ctheta)) * (1.0f + lam[2]*expf(lam[3]*gamma) + lam[4]*cgamma*cgamma);
}
__device float3 sky_radiance(KernelGlobals *kg, float3 dir)
{
/* convert vector to spherical coordinates */
float2 spherical = direction_to_spherical(dir);
float theta = spherical.x;
float phi = spherical.y;
/* angle between sun direction and dir */
float gamma = sky_angle_between(theta, phi, kernel_data.sunsky.theta, kernel_data.sunsky.phi);
/* clamp theta to horizon */
theta = min(theta, M_PI_2_F - 0.001f);
/* compute xyY color space values */
float x = kernel_data.sunsky.zenith_x * sky_perez_function(kernel_data.sunsky.perez_x, theta, gamma);
float y = kernel_data.sunsky.zenith_y * sky_perez_function(kernel_data.sunsky.perez_y, theta, gamma);
float Y = kernel_data.sunsky.zenith_Y * sky_perez_function(kernel_data.sunsky.perez_Y, theta, gamma);
/* convert to RGB */
float3 xyz = xyY_to_xyz(x, y, Y);
return xyz_to_rgb(xyz.x, xyz.y, xyz.z);
}
__device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack, uint dir_offset, uint out_offset)
{
float3 dir = stack_load_float3(stack, dir_offset);
float3 f = sky_radiance(kg, dir);
stack_store_float3(stack, out_offset, f);
}
CCL_NAMESPACE_END
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