<canvas id="canvas"></canvas>

<!-- vertex shader -->
<script id="vs" type="f">
	attribute vec2 position;
	attribute vec2 texcoord;

	uniform mat3 u_matrix;

	varying vec2 v_texcoord;

	void main() {
		 gl_Position = vec4(u_matrix * vec3(position, 1), 1);
		 v_texcoord = texcoord;
	}
</script>

<!-- fragment shader -->
<script id="fs" type="f">
	precision mediump float;

	uniform vec2 u_mouse;

	uniform sampler2D u_originalImage;
	uniform sampler2D u_mapImage;

	varying vec2 v_texcoord;

	void main() {
		 vec4 depthDistortion = texture2D(u_mapImage, v_texcoord);
		 float parallaxMult = depthDistortion.r;

		 vec2 parallax = (u_mouse) * parallaxMult;

		 vec4 original = texture2D(u_originalImage, (v_texcoord + parallax));
		 gl_FragColor = original;
	}
</script>
body { margin: 0;}
canvas { width: 100vw; height: 100vh; display: block; }
"use strict";

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  const canvas = document.getElementById("canvas");
  const gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  let originalImage = { width: 1, height: 1 }; // replaced after loading
  const originalTexture = twgl.createTexture(gl, {
    src: "https://res.cloudinary.com/ameyachikramane-com/image/upload/v1552413007/pic.jpg", 
    crossOrigin: " ",
  }, (err, texture, source) => {
    originalImage = source;
  });
  
  const mapTexture = twgl.createTexture(gl, {
    src: "https://res.cloudinary.com/ameyachikramane-com/image/upload/v1552413008/map.jpg", crossOrigin: " ",
  });
  

  // compile shaders, link program, lookup location
  const programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

  // calls gl.createBuffer, gl.bindBuffer, gl.bufferData for a quad
  const bufferInfo = twgl.primitives.createXYQuadBufferInfo(gl);

  const mouse = [0, 0];
  document.addEventListener('mousemove', (event) => {
    mouse[0] = (event.clientX / gl.canvas.clientWidth  * 2 - 1) * -0.02;
    mouse[1] = (event.clientY / gl.canvas.clientHeight * 2 - 1) * -0.02;
  });
	
	document.addEventListener('touchmove', (event) => {
    mouse[0] = (event.touches[0].clientX / gl.canvas.clientWidth  * 2 - 1) * -0.02;
    mouse[1] = (event.touches[0].clientY / gl.canvas.clientHeight * 2 - 1) * -0.02;
  });
	
	document.addEventListener('touchend', (event) => {
    mouse[0] = 0;
    mouse[1] = 0;
  });
	
	var nMouse = [0, 0];
	var oMouse = [0, 0];
  
  requestAnimationFrame(render);
  
  function render() {
    
    twgl.resizeCanvasToDisplaySize(gl.canvas);

    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    gl.clearColor(0, 0, 0, 0);
    gl.clear(gl.COLOR_BUFFER_BIT);

    gl.useProgram(programInfo.program);

    // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
    twgl.setBuffersAndAttributes(gl, programInfo, bufferInfo);

    const canvasAspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
    const imageAspect = originalImage.width / originalImage.height;
    const mat = m3.scaling(imageAspect / canvasAspect, -1);
		
		nMouse[0] += (mouse[0] - nMouse[0]) * 0.05;
		nMouse[1] += (mouse[1] - nMouse[1]) * 0.05;
			
    // calls gl.activeTexture, gl.bindTexture, gl.uniformXXX
    twgl.setUniforms(programInfo, {
      u_matrix: mat,
      u_originalImage: originalTexture,
      u_mapImage: mapTexture,
      u_mouse: nMouse,
    });
		
    // calls gl.drawArrays or gl.drawElements
    twgl.drawBufferInfo(gl, bufferInfo);
    
    requestAnimationFrame(render);
  }
}

main();

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdn.rawgit.com/greggman/twgl.js/master/dist/4.x/twgl-full.min.js
  2. https://webglfundamentals.org/webgl/resources/m3.js