in vec4 uvcoordsvar;

out vec4 FragColor;

uniform usampler2D outlineId;
uniform sampler2D outlineDepth;
uniform sampler2D sceneDepth;

uniform int idOffsets[4];

uniform float alphaOcclu;
uniform vec2 viewportSize;

vec4 convert_id_to_color(int id)
{
  if (id == 0) {
    return vec4(0.0);
  }
  if (id < idOffsets[1]) {
    return colorActive;
  }
  else if (id < idOffsets[2]) {
    return colorSelect;
  }
  else if (id < idOffsets[3]) {
    return colorDupliSelect;
  }
  else {
    return colorTransform;
  }
}

void main()
{
  ivec2 texel = ivec2(gl_FragCoord.xy);

#ifdef GPU_ARB_texture_gather
  vec2 texel_size = 1.0 / vec2(textureSize(outlineId, 0).xy);
  vec2 uv = ceil(gl_FragCoord.xy) * texel_size;

  /* Samples order is CW starting from top left. */
  uvec4 tmp1 = textureGather(outlineId, uv - texel_size);
  uvec4 tmp2 = textureGather(outlineId, uv);

  uint ref_id = tmp1.y;
  uvec4 id = uvec4(tmp1.xz, tmp2.xz);
#else
  uvec4 id;
  uint ref_id = texelFetch(outlineId, texel, 0).r;
  id.x = texelFetchOffset(outlineId, texel, 0, ivec2(-1, 0)).r;
  id.y = texelFetchOffset(outlineId, texel, 0, ivec2(0, -1)).r;
  id.z = texelFetchOffset(outlineId, texel, 0, ivec2(0, 1)).r;
  id.w = texelFetchOffset(outlineId, texel, 0, ivec2(1, 0)).r;
#endif

#ifdef WIRE
  /* We want only 2px outlines. */
  /* TODO optimize, don't sample if we don't need to. */
  id.xy = uvec2(ref_id);
#endif

  bool outline = any(notEqual(id, uvec4(ref_id)));

  ivec2 depth_texel = texel;
  /* If texel is an outline but has no valid id ...
   * replace id and depth texel by a valid one.
   * This keeps the outline thickness consistent everywhere. */
  if (ref_id == 0u && outline) {
    depth_texel = (id.x != 0u) ? texel + ivec2(-1, 0) : depth_texel;
    depth_texel = (id.y != 0u) ? texel + ivec2(0, -1) : depth_texel;
    depth_texel = (id.z != 0u) ? texel + ivec2(0, 1) : depth_texel;
    depth_texel = (id.w != 0u) ? texel + ivec2(1, 0) : depth_texel;

    ref_id = (id.x != 0u) ? id.x : ref_id;
    ref_id = (id.y != 0u) ? id.y : ref_id;
    ref_id = (id.z != 0u) ? id.z : ref_id;
    ref_id = (id.w != 0u) ? id.w : ref_id;
  }

  float ref_depth = texelFetch(outlineDepth, depth_texel, 0).r;
  float scene_depth = texelFetch(sceneDepth, depth_texel, 0).r;

  /* Avoid bad cases of zfighting for occlusion only. */
  const float epsilon = 3.0 / 8388608.0;
  bool occluded = (ref_depth > scene_depth + epsilon);

  FragColor = convert_id_to_color(int(ref_id));
  FragColor.a *= (occluded) ? alphaOcclu : 1.0;
  FragColor.a = (outline) ? FragColor.a : 0.0;
}