/*
 * 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

/* Sky texture */

ccl_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);
}

/*
 * "A Practical Analytic Model for Daylight"
 * A. J. Preetham, Peter Shirley, Brian Smits
 */
ccl_device float sky_perez_function(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);
}

ccl_device float3 sky_radiance_old(KernelGlobals *kg, float3 dir,
                                 float sunphi, float suntheta,
                                 float radiance_x, float radiance_y, float radiance_z,
                                 float *config_x, float *config_y, float *config_z)
{
	/* 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, suntheta, sunphi);

	/* clamp theta to horizon */
	theta = min(theta, M_PI_2_F - 0.001f);

	/* compute xyY color space values */
	float x = radiance_y * sky_perez_function(config_y, theta, gamma);
	float y = radiance_z * sky_perez_function(config_z, theta, gamma);
	float Y = radiance_x * sky_perez_function(config_x, theta, gamma);

	/* convert to RGB */
	float3 xyz = xyY_to_xyz(x, y, Y);
	return xyz_to_rgb(xyz.x, xyz.y, xyz.z);
}

/*
 * "An Analytic Model for Full Spectral Sky-Dome Radiance"
 * Lukas Hosek, Alexander Wilkie
 */
ccl_device float sky_radiance_internal(float *configuration, float theta, float gamma)
{
	float ctheta = cosf(theta);
	float cgamma = cosf(gamma);

	float expM = expf(configuration[4] * gamma);
	float rayM = cgamma * cgamma;
	float mieM = (1.0f + rayM) / powf((1.0f + configuration[8]*configuration[8] - 2.0f*configuration[8]*cgamma), 1.5f);
	float zenith = sqrtf(ctheta);

	return (1.0f + configuration[0] * expf(configuration[1] / (ctheta + 0.01f))) *
		(configuration[2] + configuration[3] * expM + configuration[5] * rayM + configuration[6] * mieM + configuration[7] * zenith);
}

ccl_device float3 sky_radiance_new(KernelGlobals *kg, float3 dir,
                                 float sunphi, float suntheta,
                                 float radiance_x, float radiance_y, float radiance_z,
                                 float *config_x, float *config_y, float *config_z)
{
	/* 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, suntheta, sunphi);

	/* clamp theta to horizon */
	theta = min(theta, M_PI_2_F - 0.001f);

	/* compute xyz color space values */
	float x = sky_radiance_internal(config_x, theta, gamma) * radiance_x;
	float y = sky_radiance_internal(config_y, theta, gamma) * radiance_y;
	float z = sky_radiance_internal(config_z, theta, gamma) * radiance_z;

	/* convert to RGB and adjust strength */
	return xyz_to_rgb(x, y, z) * (M_2PI_F/683);
}

ccl_device void svm_node_tex_sky(KernelGlobals *kg, ShaderData *sd, float *stack, uint4 node, int *offset)
{
	/* Define variables */
	float sunphi, suntheta, radiance_x, radiance_y, radiance_z;
	float config_x[9], config_y[9], config_z[9];
	
	/* Load data */
	uint dir_offset = node.y;
	uint out_offset = node.z;
	int sky_model = node.w;

	float4 data = read_node_float(kg, offset);
	sunphi = data.x;
	suntheta = data.y;
	radiance_x = data.z;
	radiance_y = data.w;
	
	data = read_node_float(kg, offset);
	radiance_z = data.x;
	config_x[0] = data.y;
	config_x[1] = data.z;
	config_x[2] = data.w;
	
	data = read_node_float(kg, offset);
	config_x[3] = data.x;
	config_x[4] = data.y;
	config_x[5] = data.z;
	config_x[6] = data.w;
	
	data = read_node_float(kg, offset);
	config_x[7] = data.x;
	config_x[8] = data.y;
	config_y[0] = data.z;
	config_y[1] = data.w;
	
	data = read_node_float(kg, offset);
	config_y[2] = data.x;
	config_y[3] = data.y;
	config_y[4] = data.z;
	config_y[5] = data.w;
	
	data = read_node_float(kg, offset);
	config_y[6] = data.x;
	config_y[7] = data.y;
	config_y[8] = data.z;
	config_z[0] = data.w;
	
	data = read_node_float(kg, offset);
	config_z[1] = data.x;
	config_z[2] = data.y;
	config_z[3] = data.z;
	config_z[4] = data.w;
	
	data = read_node_float(kg, offset);
	config_z[5] = data.x;
	config_z[6] = data.y;
	config_z[7] = data.z;
	config_z[8] = data.w;
	
	float3 dir = stack_load_float3(stack, dir_offset);
	float3 f;

	/* Compute Sky */
	if(sky_model == 0) {
		f = sky_radiance_old(kg, dir, sunphi, suntheta,
	                             radiance_x, radiance_y, radiance_z,
	                             config_x, config_y, config_z);
	}
	else {
		f = sky_radiance_new(kg, dir, sunphi, suntheta,
	                             radiance_x, radiance_y, radiance_z,
	                             config_x, config_y, config_z);
	}

	stack_store_float3(stack, out_offset, f);
}

CCL_NAMESPACE_END