/*
 * 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.
 */

#include "stdosl.h"
#include "node_color.h"

float sky_angle_between(float thetav, float phiv, float theta, float phi)
{
	float cospsi = sin(thetav) * sin(theta) * cos(phi - phiv) + cos(thetav) * cos(theta);

	if (cospsi > 1.0)
		return 0.0;
	if (cospsi < -1.0)
		return M_PI;

	return acos(cospsi);
}

vector sky_spherical_coordinates(vector dir)
{
	return vector(acos(dir[2]), atan2(dir[0], dir[1]), 0);
}

/* Preetham */
float sky_perez_function(float lam[9], float theta, float gamma)
{
	float ctheta = cos(theta);
	float cgamma = cos(gamma);

	return (1.0 + lam[0] * exp(lam[1] / ctheta)) * (1.0 + lam[2] * exp(lam[3] * gamma) + lam[4] * cgamma * cgamma);
}

color sky_radiance_old(normal dir,
                       float sunphi, float suntheta, color radiance,
                       float config_x[9], float config_y[9], float config_z[9])
{
	/* convert vector to spherical coordinates */
	vector spherical = sky_spherical_coordinates(dir);
	float theta = spherical[0];
	float phi = spherical[1];

	/* 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 - 0.001);

	/* compute xyY color space values */
	float x = radiance[1] * sky_perez_function(config_y, theta, gamma);
	float y = radiance[2] * sky_perez_function(config_z, theta, gamma);
	float Y = radiance[0] * sky_perez_function(config_x, theta, gamma);

	/* convert to RGB */
	color xyz = xyY_to_xyz(x, y, Y);
	return xyz_to_rgb(xyz[0], xyz[1], xyz[2]);
}

/* Hosek / Wilkie */
float sky_radiance_internal(float config[9], float theta, float gamma)
{
	float ctheta = cos(theta);
	float cgamma = cos(gamma);
	
	float expM = exp(config[4] * gamma);
	float rayM = cgamma * cgamma;
	float mieM = (1.0 + rayM) / pow((1.0 + config[8] * config[8] - 2.0 * config[8] * cgamma), 1.5);
	float zenith = sqrt(ctheta);

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

color sky_radiance_new(normal dir,
                       float sunphi, float suntheta, color radiance,
                       float config_x[9], float config_y[9], float config_z[9])
{
	/* convert vector to spherical coordinates */
	vector spherical = sky_spherical_coordinates(dir);
	float theta = spherical[0];
	float phi = spherical[1];

	/* 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 - 0.001);

	/* compute xyz color space values */
	float x = sky_radiance_internal(config_x, theta, gamma) * radiance[0];
	float y = sky_radiance_internal(config_y, theta, gamma) * radiance[1];
	float z = sky_radiance_internal(config_z, theta, gamma) * radiance[2];

	/* convert to RGB and adjust strength */
	return xyz_to_rgb(x, y, z) * (M_2PI / 683);
}

shader node_sky_texture(
	int use_mapping = 0,
	matrix mapping = matrix(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
	vector Vector = P,
	string sky_model = "Hosek / Wilkie",
	float theta = 0.0,
	float phi = 0.0,
	color radiance = color(0.0, 0.0, 0.0),
	float config_x[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
	float config_y[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
	float config_z[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
	output color Color = color(0.0, 0.0, 0.0))
{
	vector p = Vector;

	if (use_mapping)
		p = transform(mapping, p);
	
	if (sky_model == "Hosek / Wilkie")
		Color = sky_radiance_new(p, phi, theta, radiance, config_x, config_y, config_z);
	else
		Color = sky_radiance_old(p, phi, theta, radiance, config_x, config_y, config_z);
}