fabric/src/filters/shaders/saturation.ts

Object model for HTML5 canvas, and SVG-to-canvas parser. Backed by jsdom and node-canvas.

export const fragmentSource = `
  precision highp float;
  uniform sampler2D uTexture;
  uniform float uSaturation;
  varying vec2 vTexCoord;
  void main() {
    vec4 color = texture2D(uTexture, vTexCoord);
    float rgMax = max(color.r, color.g);
    float rgbMax = max(rgMax, color.b);
    color.r += rgbMax != color.r ? (rgbMax - color.r) * uSaturation : 0.00;
    color.g += rgbMax != color.g ? (rgbMax - color.g) * uSaturation : 0.00;
    color.b += rgbMax != color.b ? (rgbMax - color.b) * uSaturation : 0.00;
    gl_FragColor = color;
  }
`;