var canvas = document.getElementById("canvas");

canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

// Initialize the GL context
var gl = canvas.getContext('webgl');
if(!gl){
  console.error("Unable to initialize WebGL.");
}

//Time
var time = 0.0;

//************** Shader sources **************

var vertexSource = `
attribute vec2 position;
void main() {
	gl_Position = vec4(position, 0.0, 1.0);
}
`;

var fragmentSource = `
precision highp float;

uniform float width;
uniform float height;
vec2 resolution = vec2(width, height);

uniform float time;

//Base values modified with depth later
float intensity = 1.0;
float radius = 0.05;

//Distance functions from 
//https://www.iquilezles.org/www/articles/distfunctions2d/distfunctions2d.htm
float triangleDist(vec2 p){ 
	const float k = sqrt(3.0);
  p.x = abs(p.x) - 1.0;
  p.y = p.y + 1.0/k;
  if( p.x+k*p.y>0.0 ) p=vec2(p.x-k*p.y,-k*p.x-p.y)/2.0;
  p.x -= clamp( p.x, -2.0, 0.0 );
  return -length(p)*sign(p.y);
}

float boxDist(vec2 p){
  vec2 d = abs(p)-1.0;
  return length(max(d,vec2(0))) + min(max(d.x,d.y),0.0);
}

float circleDist( vec2 p){
  return length(p) - 1.0;
}

//https://www.shadertoy.com/view/3s3GDn
float getGlow(float dist, float radius, float intensity){
  return pow(radius/dist, intensity);
}

void main(){
    
	vec2 uv = gl_FragCoord.xy/resolution.xy;
  float widthHeightRatio = resolution.x/resolution.y;
  vec2 centre;
  vec2 pos;
	
  float t = time * 0.05;
    
  float dist;
  float glow;
  vec3 col = vec3(0);
    
  //The spacing between shapes
  float scale = 500.0;
  //Number of shapes
  const int layers = 15;
    
  float depth;
  vec2 bend;
    
  vec3 purple = vec3(0.611, 0.129, 0.909);
  vec3 green = vec3(0.133, 0.62, 0.698);
    
  float angle;
  float rotationAngle;
  mat2 rotation;
    
  //For movement of the anchor point in time
  float d = 2.5*(sin(t) + sin(3.0*t));

  //Create an out of frame anchor point where all shapes converge to    
  vec2 anchor = vec2(0.5 + cos(d), 0.5 + sin(d));
    
  //Create light purple glow at the anchor loaction
  pos = anchor - uv;
  pos.y /= widthHeightRatio;
  dist = length(pos);
  glow = getGlow(dist, 0.25, 3.5);
  col += glow * vec3(0.6,0.4,1.0);
    
	for(int i = 0; i < layers; i++){
        
  	//Time varying depth information depending on layer
    depth = fract(float(i)/float(layers) + t);

    //Move the focus of the camera in a circle
    centre = vec2(0.5 + 0.2 * sin(t), 0.5 + 0.2 * cos(t));
        
   	//Position shapes between the anchor and the camera focus based on depth
   	bend = mix(anchor, centre, depth);
     	
    pos = bend - uv;
   	pos.y /= widthHeightRatio;

    //Rotate shapes
    rotationAngle = 3.14 * sin(depth + fract(t) * 6.28) + float(i);
    rotation = mat2(cos(rotationAngle), -sin(rotationAngle), 
                    sin(rotationAngle),  cos(rotationAngle));
        
    pos *= rotation;
        
    //Position shapes according to depth
    pos *= mix(scale, 0.0, depth);
    	
    float m = mod(float(i), 3.0);
    if(m == 0.0){
    	dist = abs(boxDist(pos));
    }else if(m == 1.0){
      dist = abs(triangleDist(pos));
    }else{
    	dist = abs(circleDist(pos));
    }
       
    //Get glow from base radius and intensity modified by depth
    glow = getGlow(dist, radius+(1.0-depth)*2.0, intensity + depth);
        
    //Find angle along shape and map from [-PI; PI] to [0; 1]
    angle = (atan(pos.y, pos.x)+3.14)/6.28;
    //Shift angle depending on layer and map to [1...0...1]
		angle = abs((2.0*fract(angle + float(i)/float(layers))) - 1.0);
        
    //White core
   	//col += 10.0*vec3(smoothstep(0.03, 0.02, dist));
        
    //Glow according to angle value
    col += glow * mix(green, purple, angle);
	}
    
  //Tone mapping
  col = 1.0 - exp(-col);

  //Gamma
  col = pow(col, vec3(0.4545));
    
  //Output to screen
  gl_FragColor = vec4(col,1.0);
}
`;

//************** Utility functions **************

window.addEventListener('resize', onWindowResize, false);

function onWindowResize(){
  canvas.width  = window.innerWidth;
  canvas.height = window.innerHeight;
	gl.viewport(0, 0, canvas.width, canvas.height);
  gl.uniform1f(widthHandle, window.innerWidth);
  gl.uniform1f(heightHandle, window.innerHeight);
}


//Compile shader and combine with source
function compileShader(shaderSource, shaderType){
  var shader = gl.createShader(shaderType);
  gl.shaderSource(shader, shaderSource);
  gl.compileShader(shader);
  if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS)){
  	throw "Shader compile failed with: " + gl.getShaderInfoLog(shader);
  }
  return shader;
}

//From https://codepen.io/jlfwong/pen/GqmroZ
//Utility to complain loudly if we fail to find the attribute/uniform
function getAttribLocation(program, name) {
  var attributeLocation = gl.getAttribLocation(program, name);
  if (attributeLocation === -1) {
  	throw 'Cannot find attribute ' + name + '.';
  }
  return attributeLocation;
}

function getUniformLocation(program, name) {
  var attributeLocation = gl.getUniformLocation(program, name);
  if (attributeLocation === -1) {
  	throw 'Cannot find uniform ' + name + '.';
  }
  return attributeLocation;
}

//************** Create shaders **************

//Create vertex and fragment shaders
var vertexShader = compileShader(vertexSource, gl.VERTEX_SHADER);
var fragmentShader = compileShader(fragmentSource, gl.FRAGMENT_SHADER);

//Create shader programs
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);

gl.useProgram(program);

//Set up rectangle covering entire canvas 
var vertexData = new Float32Array([
  -1.0,  1.0, 	// top left
  -1.0, -1.0, 	// bottom left
   1.0,  1.0, 	// top right
   1.0, -1.0, 	// bottom right
]);

//Create vertex buffer
var vertexDataBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexDataBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertexData, gl.STATIC_DRAW);

// Layout of our data in the vertex buffer
var positionHandle = getAttribLocation(program, 'position');

gl.enableVertexAttribArray(positionHandle);
gl.vertexAttribPointer(positionHandle,
  2, 				// position is a vec2 (2 values per component)
  gl.FLOAT, // each component is a float
  false, 		// don't normalize values
  2 * 4, 		// two 4 byte float components per vertex (32 bit float is 4 bytes)
  0 				// how many bytes inside the buffer to start from
  );

//Set uniform handle
var timeHandle = getUniformLocation(program, 'time');
var widthHandle = getUniformLocation(program, 'width');
var heightHandle = getUniformLocation(program, 'height');

gl.uniform1f(widthHandle, window.innerWidth);
gl.uniform1f(heightHandle, window.innerHeight);

var lastFrame = Date.now();
var thisFrame;

function draw(){
	
  //Update time
	thisFrame = Date.now();
	time += (thisFrame - lastFrame)/1000;	
	lastFrame = thisFrame;

	//Send uniforms to program
  gl.uniform1f(timeHandle, time);
  //Draw a triangle strip connecting vertices 0-4
  gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

  requestAnimationFrame(draw);
}

draw();