vertexAttribPointer

index85.html
var canvas = document.getElementById("canvas");

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

var gl = canvas.getContext('webgl');
if (!gl) {
    console.error("Unable to initialize WebGL.");
}
var time = 0.0;
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;

    float intensity = 1.0;
    float radius = 0.05;

    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);

        float scale = 500.0;
        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;
}

//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 **************
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() {
    thisFrame = Date.now();
    time += (thisFrame - lastFrame) / 1000;
    lastFrame = thisFrame;
    gl.uniform1f(timeHandle, time);
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
    requestAnimationFrame(draw);
}

draw();