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

#include "node_color.h"
#include "stdcycles.h"

vector environment_texture_direction_to_equirectangular(vector dir)
{
  float u = -atan2(dir[1], dir[0]) / (M_2PI) + 0.5;
  float v = atan2(dir[2], hypot(dir[0], dir[1])) / M_PI + 0.5;

  return vector(u, v, 0.0);
}

vector environment_texture_direction_to_mirrorball(vector idir)
{
  vector dir = idir;
  dir[1] -= 1.0;

  float div = 2.0 * sqrt(max(-0.5 * dir[1], 0.0));
  if (div > 0.0)
    dir /= div;

  float u = 0.5 * (dir[0] + 1.0);
  float v = 0.5 * (dir[2] + 1.0);

  return vector(u, v, 0.0);
}

shader node_environment_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 filename = "",
    string projection = "equirectangular",
    string interpolation = "linear",
    int compress_as_srgb = 0,
    int ignore_alpha = 0,
    int unassociate_alpha = 0,
    int is_float = 1,
    output color Color = 0.0,
    output float Alpha = 1.0)
{
  vector p = Vector;

  if (use_mapping)
    p = transform(mapping, p);

  p = normalize(p);

  if (projection == "equirectangular")
    p = environment_texture_direction_to_equirectangular(p);
  else
    p = environment_texture_direction_to_mirrorball(p);

  /* todo: use environment for better texture filtering of equirectangular */
  Color = (color)texture(
      filename, p[0], 1.0 - p[1], "wrap", "periodic", "interp", interpolation, "alpha", Alpha);

  if (ignore_alpha) {
    Alpha = 1.0;
  }
  else if (unassociate_alpha) {
    Color = color_unpremultiply(Color, Alpha);

    if (!is_float)
      Color = min(Color, 1.0);
  }

  if (compress_as_srgb)
    Color = color_srgb_to_scene_linear(Color);
}