/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
 *
 * SPDX-License-Identifier: Apache-2.0 */

#include "node_color.h"
#include "stdcycles.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_preetham(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_hosek(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);
}

/* Nishita improved */
vector geographical_to_direction(float lat, float lon)
{
  return vector(cos(lat) * cos(lon), cos(lat) * sin(lon), sin(lat));
}

float precise_angle(vector a, vector b)
{
  return 2.0 * atan2(length(a - b), length(a + b));
}

color sky_radiance_nishita(vector dir, float nishita_data[10], string filename)
{
  /* definitions */
  float sun_elevation = nishita_data[6];
  float sun_rotation = nishita_data[7];
  float angular_diameter = nishita_data[8];
  float sun_intensity = nishita_data[9];
  int sun_disc = angular_diameter > 0;
  float alpha = 1.0;
  color xyz;
  /* convert dir to spherical coordinates */
  vector direction = sky_spherical_coordinates(dir);

  /* render above the horizon */
  if (dir[2] >= 0.0) {
    /* definitions */
    vector sun_dir = geographical_to_direction(sun_elevation, sun_rotation + M_PI_2);
    float sun_dir_angle = precise_angle(dir, sun_dir);
    float half_angular = angular_diameter * 0.5;
    float dir_elevation = M_PI_2 - direction[0];

    /* If the ray is inside the sun disc, render it, otherwise render the sky.
     * Alternatively, ignore the sun if we're evaluating the background texture. */
    if (sun_dir_angle < half_angular && sun_disc == 1 && raytype("importance_bake") != 1) {
      /* get 2 pixels data */
      color pixel_bottom = color(nishita_data[0], nishita_data[1], nishita_data[2]);
      color pixel_top = color(nishita_data[3], nishita_data[4], nishita_data[5]);
      float y;

      /* sun interpolation */
      if (sun_elevation - half_angular > 0.0) {
        if ((sun_elevation + half_angular) > 0.0) {
          y = ((dir_elevation - sun_elevation) / angular_diameter) + 0.5;
          xyz = mix(pixel_bottom, pixel_top, y) * sun_intensity;
        }
      }
      else {
        if (sun_elevation + half_angular > 0.0) {
          y = dir_elevation / (sun_elevation + half_angular);
          xyz = mix(pixel_bottom, pixel_top, y) * sun_intensity;
        }
      }
      /* limb darkening, coefficient is 0.6f */
      float angle_fraction = sun_dir_angle / half_angular;
      float limb_darkening = (1.0 - 0.6 * (1.0 - sqrt(1.0 - angle_fraction * angle_fraction)));
      xyz *= limb_darkening;
    }
    /* sky */
    else {
      /* sky interpolation */
      float x = (direction[1] + M_PI + sun_rotation) / M_2PI;
      /* more pixels toward horizon compensation */
      float y = 1.0 - sqrt(dir_elevation / M_PI_2);
      if (x > 1.0) {
        x = x - 1.0;
      }
      xyz = (color)texture(filename, x, y, "wrap", "clamp", "interp", "linear", "alpha", alpha);
    }
  }
  /* ground */
  else {
    if (dir[2] < -0.4) {
      xyz = color(0, 0, 0);
    }
    else {
      /* black ground fade */
      float mul = pow(1.0 + dir[2] * 2.5, 3.0);
      /* interpolation */
      float x = (direction[1] + M_PI + sun_rotation) / M_2PI;
      float y = 1.5;
      if (x > 1.0) {
        x = x - 1.0;
      }
      xyz = (color)texture(
                filename, x, y, "wrap", "periodic", "interp", "linear", "alpha", alpha) *
            mul;
    }
  }
  /* convert to RGB */
  return xyz_to_rgb(xyz[0], xyz[1], xyz[2]);
}

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_type = "hosek_wilkie",
    float theta = 0.0,
    float phi = 0.0,
    string filename = "",
    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},
    float nishita_data[10] = {0.0, 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_type == "nishita_improved")
    Color = sky_radiance_nishita(p, nishita_data, filename);
  if (sky_type == "hosek_wilkie")
    Color = sky_radiance_hosek(p, phi, theta, radiance, config_x, config_y, config_z);
  if (sky_type == "preetham")
    Color = sky_radiance_preetham(p, phi, theta, radiance, config_x, config_y, config_z);
}
