<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 vec2 u_res;
	varying vec2 v_texcoord;

	void main() {
		vec2 position = v_texcoord;
		
		vec3 lastcolor = vec3(0.0, 0.0, 0.0);
		float color = 0.009 / distance(position, u_mouse);

		vec3 o = vec3(0);
		o += lastcolor * 0.5;
		o += vec3(color) * vec3(1.0, 0.2, 1.0);
		o += (length(position - u_mouse) * 0.01) / (length((position - (vec2(.5) - (u_mouse - vec2(0.25)))))) * vec3(1.0, 0.9, 1.0);
		o += (u_mouse.x * 0.002) / (length((position - u_mouse) * vec2(1.62, 13.0))) * vec3(02.2, 5.4, u_mouse.y * 30.8);

		gl_FragColor = vec4( o, 1.0 );
	}
</script>

body {
	margin: 0;	
}

canvas {
	width: 100%;
	height: 100%;
	display: block;
	position: absolute;
	top: 0;
	left: 0;
	z-index: 1;
}

"use strict";

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  const canvas = document.getElementById("canvas");
  const gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }
  
  // 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];
  canvas.addEventListener('mousemove', (event) => {
    mouse[0] = (event.clientX / gl.canvas.clientWidth);
    mouse[1] = (event.clientY / gl.canvas.clientHeight);
  });
	
	canvas.addEventListener('mouseout', (event) => {
    mouse[0] = 0.5;
    mouse[1] = 0.5;
  });
	
	canvas.addEventListener('touchmove', (event) => {
    mouse[0] = (event.touches[0].clientX / gl.canvas.clientWidth );
    mouse[1] = (event.touches[0].clientY / gl.canvas.clientHeight);
  });
	
	canvas.addEventListener('touchend', (event) => {
    mouse[0] = 0.5;
    mouse[1] = 0.5;
  });
	
	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 mat = m3.scaling(canvasAspect / 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_mouse: nMouse,
			u_res: [gl.canvas.clientWidth, gl.canvas.clientHeight],
    });
		
    // calls gl.drawArrays or gl.drawElements
    twgl.drawBufferInfo(gl, bufferInfo);
    
    requestAnimationFrame(render);
  }
}

main();