gl-react/docs/examples/2.md

Saturate an Image

Effects on images like saturation, contrast, brightness, inverse, hue,... are very easy to implement in GLSL. Here is the example of Saturation.

<Saturation
  width={256}
  height={171}
  factor={saturationFactor}
  image={{ uri: "http://i.imgur.com/iPKTONG.jpg" }}
/>

Implementation

const React = require("react-native");
const GL = require("gl-react-native");

const shaders = GL.Shaders.create({
  saturation: {
    frag: `
precision highp float;
varying vec2 uv;
uniform sampler2D image;
uniform float factor;

void main () {
  vec4 c = texture2D(image, uv);
  // Algorithm from Chapter 16 of OpenGL Shading Language
  const vec3 W = vec3(0.2125, 0.7154, 0.0721);
  gl_FragColor = vec4(mix(vec3(dot(c.rgb, W)), c.rgb, factor), c.a);
}
    `
  }
});

module.exports = GL.createComponent(
  ({ factor, image, ...rest }) =>
  <GL.View
    {...rest}
    shader={shaders.saturation}
    uniforms={{ factor, image }}
  />,
{ displayName: "Saturation" });

GL.View supports uniforms props that allow to send to the shader any parameters from the JavaScript world.

In this example, we send the factor number (that come from props) and we also send the image. The image have the same format as the source passed in an <Image/>.