#ifdef GL_ES

precision mediump float;

#endif

uniform mat3      worldToOutput;

uniform sampler2D inputImage[2];

uniform mat3      outputToInput[2];

uniform bool bhue;    // Blend HUE?

uniform bool bsat;    // Blend Saturation?

uniform bool blum;    // Blend Luminosity?

uniform float balpha; // Blending Alpha

uniform bool bmask;   // Base mask?

// ---------------------------

// Blending calculations from:

// https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_blend_equation_advanced.txt

float minv3(vec3 c)

{

  return min(min(c.r, c.g), c.b);

}

float maxv3(vec3 c)

{

  return max(max(c.r, c.g), c.b);

}

float lumv3(vec3 c)

{

  return dot(c, vec3(0.30, 0.59, 0.11));

}

float satv3(vec3 c)

{

  return maxv3(c) - minv3(c);

}

// If any color components are outside [0,1], adjust the color to get the components in range.

vec3 ClipColor(vec3 color)

{

  float lum = lumv3(color);

  float mincol = minv3(color);

  float maxcol = maxv3(color);

  if (mincol < 0.0) {

    color = lum + ((color-lum) * lum) / (lum-mincol);

  }

  if (maxcol > 1.0) {

    color = lum + ((color-lum) * (1.0 -lum)) / (maxcol-lum);

  }

  return color;

}

// Take the base RGB color <cbase> and override its luminosity</cbase>

// with that of the RGB color <clum>.</clum>

vec3 SetLum(vec3 cbase, vec3 clum)

{

  float lbase = lumv3(cbase);

  float llum = lumv3(clum);

  float ldiff = llum - lbase;

  vec3 color = cbase + vec3(ldiff);

  return ClipColor(color);

}

// Take the base RGB color <cbase> and override its saturation with</cbase>

// that of the RGB color <csat>.  The override the luminosity of the</csat>

// result with that of the RGB color <clum>.</clum>

vec3 SetLumSat(vec3 cbase, vec3 csat, vec3 clum)

{

  float minbase = minv3(cbase);

  float sbase = satv3(cbase);

  float ssat = satv3(csat);

  vec3 color;

  if (sbase > 0.0) {

    // Equivalent (modulo rounding errors) to setting the

    // smallest (R,G,B) component to 0, the largest to <ssat>,</ssat>

    // and interpolating the "middle" component based on its

    // original value relative to the smallest/largest.

    color = (cbase - minbase) * ssat / sbase;

  } else {

    color = vec3(0.0);

  }

  return SetLum(color, clum);

}

// ---------------------------

void main( void )

{

  // Read sources

  vec2 fg_texPos = (outputToInput[0] * vec3(gl_FragCoord.xy, 1.0)).xy;

  vec2 bg_texPos = (outputToInput[1] * vec3(gl_FragCoord.xy, 1.0)).xy;

  vec4 fg_frag = texture2D(inputImage[0], fg_texPos);

  vec4 bg_frag = texture2D(inputImage[1], bg_texPos);

  // De-premultiplication of textures

  vec3 fg_pix = vec3(0.0);

  if (fg_frag.a > 0.0) fg_pix = fg_frag.rgb / fg_frag.a;

  vec3 bg_pix = vec3(0.0);

  if (bg_frag.a > 0.0) bg_pix = bg_frag.rgb / bg_frag.a;

  // Figure out output alpha

  float fg_alpha = fg_frag.a * balpha;

  float bg_alpha = bg_frag.a;

  if (bmask) {

    gl_FragColor.a = bg_alpha;

  } else {

    gl_FragColor.a = bg_alpha + fg_alpha * (1.0 - bg_alpha);

  }

  if (gl_FragColor.a <= 0.0) discard;

  // Perform blending

  vec3 o_pix = SetLumSat(bhue ? fg_pix : bg_pix, bsat ? fg_pix : bg_pix, blum ? fg_pix : bg_pix);

  vec3 b_pix = bmask ? vec3(0.0) : fg_pix;

  gl_FragColor.rgb = bg_pix * bg_alpha * (1.0 - fg_alpha) + mix(b_pix, o_pix, bg_alpha) * fg_alpha;

}