Happy Holi 2024 Design Animation
Tags: javascript, animation, webdev, css
Published: 2024-03-25 12:04:20

On this Holi day, I thought of sprinkling some coding colors to celebrate the festival digitally. Because why just throw powdered colors when you can splash pixels with code? Let’s turn this festival of India into a coding fiesta!

### Introduction

I am designing the festival to a whole new level — a digital Holi Celebration filled with CSS and JS colors and virtual sparkles!


### Visual Demonstration

A codepen to play with 
The below demo consist of the following features

* Change color with mouse click

* Sparkle color as you move the mouse

{% codepen https://codepen.io/ssukhpinder/pen/ExJXggX %}

## Complete Code

Please find below the complete or refer to the [Github gist](https://gist.github.com/ssukhpinder/b3021999768db2a40ecfa612d8eef38a)

### Html code
```html
    <canvas></canvas>
    <div>Happy Holi 2024</div>
```
### CSS
```css
    html, body {
        overflow: hidden;
        padding:50px;
        color:#fff;
    }

    canvas {
     position: fixed;
     top:0;
     left:0;
     width:100%;
     height:100%;
     z-index:0.5;
     opacity:1;
    }
    div{
        position:relative;
        z-index:1;
        font-size:70px;
        padding:0;
        display: table;
        margin:auto;
        letter-spacing:2px;
    }
```
### Javascript
```javascript
/*
ORIGINAL WORK
https://codepen.io/PavelDoGreat/pen/zdWzEL
*/

'use strict';

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

var canvas = document.getElementsByTagName('canvas')[0];
canvas.width = canvas.clientWidth;
canvas.height = canvas.clientHeight;

var params = { alpha: false, depth: false, stencil: false, antialias: false };
var gl = canvas.getContext('webgl2', params);
var isWebGL2 = !!gl;
if (!isWebGL2) {
    gl = canvas.getContext('webgl', params) || canvas.getContext('experimental-webgl', params);
}
gl.clearColor(0.0, 0.0, 0.0, 1.0);

var halfFloat = gl.getExtension('OES_texture_half_float');
var support_linear_float = gl.getExtension('OES_texture_half_float_linear');
if (isWebGL2) {
    gl.getExtension('EXT_color_buffer_float');
    support_linear_float = gl.getExtension('OES_texture_float_linear');
}

var TEXTURE_DOWNSAMPLE = 1;
var DENSITY_DISSIPATION = 0.98;
var VELOCITY_DISSIPATION = 0.99;
var SPLAT_RADIUS = 0.005;
var CURL = 30;
var PRESSURE_ITERATIONS = 25;

var GLProgram = function () {
    function GLProgram(vertexShader, fragmentShader) {
        _classCallCheck(this, GLProgram);

        this.uniforms = {};
        this.program = gl.createProgram();

        gl.attachShader(this.program, vertexShader);
        gl.attachShader(this.program, fragmentShader);
        gl.linkProgram(this.program);

        if (!gl.getProgramParameter(this.program, gl.LINK_STATUS)) throw gl.getProgramInfoLog(this.program);

        var uniformCount = gl.getProgramParameter(this.program, gl.ACTIVE_UNIFORMS);
        for (var i = 0; i < uniformCount; i++) {
            var uniformName = gl.getActiveUniform(this.program, i).name;
            this.uniforms[uniformName] = gl.getUniformLocation(this.program, uniformName);
        }
    }

    GLProgram.prototype.bind = function bind() {
        gl.useProgram(this.program);
    };

    return GLProgram;
}();

function compileShader(type, source) {
    var shader = gl.createShader(type);
    gl.shaderSource(shader, source);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) throw gl.getShaderInfoLog(shader);

    return shader;
};

var baseVertexShader = compileShader(gl.VERTEX_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    attribute vec2 aPosition;\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform vec2 texelSize;\n\n    void main () {\n        vUv = aPosition * 0.5 + 0.5;\n        vL = vUv - vec2(texelSize.x, 0.0);\n        vR = vUv + vec2(texelSize.x, 0.0);\n        vT = vUv + vec2(0.0, texelSize.y);\n        vB = vUv - vec2(0.0, texelSize.y);\n        gl_Position = vec4(aPosition, 0.0, 1.0);\n    }\n');

var displayShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uTexture;\n\n    void main () {\n        gl_FragColor = texture2D(uTexture, vUv);\n    }\n');

var splatShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    uniform sampler2D uTarget;\n    uniform float aspectRatio;\n    uniform vec3 color;\n    uniform vec2 point;\n    uniform float radius;\n\n    void main () {\n        vec2 p = vUv - point.xy;\n        p.x *= aspectRatio;\n        vec3 splat = exp(-dot(p, p) / radius) * color;\n        vec3 base = texture2D(uTarget, vUv).xyz;\n        gl_FragColor = vec4(base + splat, 1.0);\n    }\n');

var advectionManualFilteringShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    uniform sampler2D uVelocity;\n    uniform sampler2D uSource;\n    uniform vec2 texelSize;\n    uniform float dt;\n    uniform float dissipation;\n\n    vec4 bilerp (in sampler2D sam, in vec2 p) {\n        vec4 st;\n        st.xy = floor(p - 0.5) + 0.5;\n        st.zw = st.xy + 1.0;\n        vec4 uv = st * texelSize.xyxy;\n        vec4 a = texture2D(sam, uv.xy);\n        vec4 b = texture2D(sam, uv.zy);\n        vec4 c = texture2D(sam, uv.xw);\n        vec4 d = texture2D(sam, uv.zw);\n        vec2 f = p - st.xy;\n        return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);\n    }\n\n    void main () {\n        vec2 coord = gl_FragCoord.xy - dt * texture2D(uVelocity, vUv).xy;\n        gl_FragColor = dissipation * bilerp(uSource, coord);\n        gl_FragColor.a = 1.0;\n    }\n');

var advectionShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    uniform sampler2D uVelocity;\n    uniform sampler2D uSource;\n    uniform vec2 texelSize;\n    uniform float dt;\n    uniform float dissipation;\n\n    void main () {\n        vec2 coord = vUv - dt * texture2D(uVelocity, vUv).xy * texelSize;\n        gl_FragColor = dissipation * texture2D(uSource, coord);\n    }\n');

var divergenceShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uVelocity;\n\n    vec2 sampleVelocity (in vec2 uv) {\n        vec2 multiplier = vec2(1.0, 1.0);\n        if (uv.x < 0.0) { uv.x = 0.0; multiplier.x = -1.0; }\n        if (uv.x > 1.0) { uv.x = 1.0; multiplier.x = -1.0; }\n        if (uv.y < 0.0) { uv.y = 0.0; multiplier.y = -1.0; }\n        if (uv.y > 1.0) { uv.y = 1.0; multiplier.y = -1.0; }\n        return multiplier * texture2D(uVelocity, uv).xy;\n    }\n\n    void main () {\n        float L = sampleVelocity(vL).x;\n        float R = sampleVelocity(vR).x;\n        float T = sampleVelocity(vT).y;\n        float B = sampleVelocity(vB).y;\n        float div = 0.5 * (R - L + T - B);\n        gl_FragColor = vec4(div, 0.0, 0.0, 1.0);\n    }\n');

var curlShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uVelocity;\n\n    void main () {\n        float L = texture2D(uVelocity, vL).y;\n        float R = texture2D(uVelocity, vR).y;\n        float T = texture2D(uVelocity, vT).x;\n        float B = texture2D(uVelocity, vB).x;\n        float vorticity = R - L - T + B;\n        gl_FragColor = vec4(vorticity, 0.0, 0.0, 1.0);\n    }\n');

var vorticityShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uVelocity;\n    uniform sampler2D uCurl;\n    uniform float curl;\n    uniform float dt;\n\n    void main () {\n        float L = texture2D(uCurl, vL).y;\n        float R = texture2D(uCurl, vR).y;\n        float T = texture2D(uCurl, vT).x;\n        float B = texture2D(uCurl, vB).x;\n        float C = texture2D(uCurl, vUv).x;\n        vec2 force = vec2(abs(T) - abs(B), abs(R) - abs(L));\n        force *= 1.0 / length(force + 0.00001) * curl * C;\n        vec2 vel = texture2D(uVelocity, vUv).xy;\n        gl_FragColor = vec4(vel + force * dt, 0.0, 1.0);\n    }\n');

var pressureShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uPressure;\n    uniform sampler2D uDivergence;\n\n    vec2 boundary (in vec2 uv) {\n        uv = min(max(uv, 0.0), 1.0);\n        return uv;\n    }\n\n    void main () {\n        float L = texture2D(uPressure, boundary(vL)).x;\n        float R = texture2D(uPressure, boundary(vR)).x;\n        float T = texture2D(uPressure, boundary(vT)).x;\n        float B = texture2D(uPressure, boundary(vB)).x;\n        float C = texture2D(uPressure, vUv).x;\n        float divergence = texture2D(uDivergence, vUv).x;\n        float pressure = (L + R + B + T - divergence) * 0.25;\n        gl_FragColor = vec4(pressure, 0.0, 0.0, 1.0);\n    }\n');

var gradientSubtractShader = compileShader(gl.FRAGMENT_SHADER, '\n    precision highp float;\n    precision mediump sampler2D;\n\n    varying vec2 vUv;\n    varying vec2 vL;\n    varying vec2 vR;\n    varying vec2 vT;\n    varying vec2 vB;\n    uniform sampler2D uPressure;\n    uniform sampler2D uVelocity;\n\n    vec2 boundary (in vec2 uv) {\n        uv = min(max(uv, 0.0), 1.0);\n        return uv;\n    }\n\n    void main () {\n        float L = texture2D(uPressure, boundary(vL)).x;\n        float R = texture2D(uPressure, boundary(vR)).x;\n        float T = texture2D(uPressure, boundary(vT)).x;\n        float B = texture2D(uPressure, boundary(vB)).x;\n        vec2 velocity = texture2D(uVelocity, vUv).xy;\n        velocity.xy -= vec2(R - L, T - B);\n        gl_FragColor = vec4(velocity, 0.0, 1.0);\n    }\n');

var blit = function () {
    gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, -1, 1, 1, 1, 1, -1]), gl.STATIC_DRAW);
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, gl.createBuffer());
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array([0, 1, 2, 0, 2, 3]), gl.STATIC_DRAW);
    gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(0);

    return function (destination) {
        gl.bindFramebuffer(gl.FRAMEBUFFER, destination);
        gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_SHORT, 0);
    };
}();

function clear(target) {
    gl.bindFramebuffer(gl.FRAMEBUFFER, target);
    gl.clear(gl.COLOR_BUFFER_BIT);
}

function createFBO(texId, w, h, internalFormat, format, type, param) {
    gl.activeTexture(gl.TEXTURE0 + texId);
    var texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, param);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, param);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    gl.texImage2D(gl.TEXTURE_2D, 0, internalFormat, w, h, 0, format, type, null);

    var fbo = gl.createFramebuffer();
    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
    gl.viewport(0, 0, w, h);
    gl.clear(gl.COLOR_BUFFER_BIT);

    return [texture, fbo, texId];
}

function createDoubleFBO(texId, w, h, internalFormat, format, type, param) {
    var fbo1 = createFBO(texId, w, h, internalFormat, format, type, param);
    var fbo2 = createFBO(texId + 1, w, h, internalFormat, format, type, param);

    return {
        get first() {
            return fbo1;
        },
        get second() {
            return fbo2;
        },
        swap: function swap() {
            var temp = fbo1;
            fbo1 = fbo2;
            fbo2 = temp;
        }
    };
}

var textureWidth = undefined;
var textureHeight = undefined;
var density = undefined;
var velocity = undefined;
var divergence = undefined;
var curl = undefined;
var pressure = undefined;

function initFramebuffers() {
    textureWidth = gl.drawingBufferWidth >> TEXTURE_DOWNSAMPLE;
    textureHeight = gl.drawingBufferHeight >> TEXTURE_DOWNSAMPLE;

    var internalFormat = isWebGL2 ? gl.RGBA16F : gl.RGBA;
    var internalFormatRG = isWebGL2 ? gl.RG16F : gl.RGBA;
    var formatRG = isWebGL2 ? gl.RG : gl.RGBA;
    var texType = isWebGL2 ? gl.HALF_FLOAT : halfFloat.HALF_FLOAT_OES;

    density = createDoubleFBO(0, textureWidth, textureHeight, internalFormat, gl.RGBA, texType, support_linear_float ? gl.LINEAR : gl.NEAREST);
    velocity = createDoubleFBO(2, textureWidth, textureHeight, internalFormatRG, formatRG, texType, support_linear_float ? gl.LINEAR : gl.NEAREST);
    divergence = createFBO(4, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
    curl = createFBO(5, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
    pressure = createDoubleFBO(6, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
}

initFramebuffers();

var displayProgram = new GLProgram(baseVertexShader, displayShader);
var splatProgram = new GLProgram(baseVertexShader, splatShader);
var advectionProgram = new GLProgram(baseVertexShader, support_linear_float ? advectionShader : advectionManualFilteringShader);
var divergenceProgram = new GLProgram(baseVertexShader, divergenceShader);
var curlProgram = new GLProgram(baseVertexShader, curlShader);
var vorticityProgram = new GLProgram(baseVertexShader, vorticityShader);
var pressureProgram = new GLProgram(baseVertexShader, pressureShader);
var gradienSubtractProgram = new GLProgram(baseVertexShader, gradientSubtractShader);

function pointerPrototype() {
    this.id = -1;
    this.x = 0;
    this.y = 0;
    this.dx = 0;
    this.dy = 0;
    this.down = false;
    this.moved = false;
    this.color = [30, 0, 300];
}

var pointers = [];
pointers.push(new pointerPrototype());

for (var i = 0; i < 10; i++) {
    var color = [Math.random() * 10, Math.random() * 10, Math.random() * 10];
    var x = canvas.width * Math.random();
    var y = canvas.height * Math.random();
    var dx = 1000 * (Math.random() - 0.5);
    var dy = 1000 * (Math.random() - 0.5);
    splat(x, y, dx, dy, color);
}

var lastTime = Date.now();
Update();

function Update() {
    resizeCanvas();

    var dt = Math.min((Date.now() - lastTime) / 1000, 0.016);
    lastTime = Date.now();

    gl.viewport(0, 0, textureWidth, textureHeight);

    advectionProgram.bind();
    gl.uniform2f(advectionProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.first[2]);
    gl.uniform1i(advectionProgram.uniforms.uSource, velocity.first[2]);
    gl.uniform1f(advectionProgram.uniforms.dt, dt);
    gl.uniform1f(advectionProgram.uniforms.dissipation, VELOCITY_DISSIPATION);
    blit(velocity.second[1]);
    velocity.swap();

    gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.first[2]);
    gl.uniform1i(advectionProgram.uniforms.uSource, density.first[2]);
    gl.uniform1f(advectionProgram.uniforms.dissipation, DENSITY_DISSIPATION);
    blit(density.second[1]);
    density.swap();

    for (var i = 0; i < pointers.length; i++) {
        var pointer = pointers[i];
        if (pointer.moved) {
            splat(pointer.x, pointer.y, pointer.dx, pointer.dy, pointer.color);
            pointer.moved = false;
        }
    }

    curlProgram.bind();
    gl.uniform2f(curlProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(curlProgram.uniforms.uVelocity, velocity.first[2]);
    blit(curl[1]);

    vorticityProgram.bind();
    gl.uniform2f(vorticityProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(vorticityProgram.uniforms.uVelocity, velocity.first[2]);
    gl.uniform1i(vorticityProgram.uniforms.uCurl, curl[2]);
    gl.uniform1f(vorticityProgram.uniforms.curl, CURL);
    gl.uniform1f(vorticityProgram.uniforms.dt, dt);
    blit(velocity.second[1]);
    velocity.swap();

    divergenceProgram.bind();
    gl.uniform2f(divergenceProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(divergenceProgram.uniforms.uVelocity, velocity.first[2]);
    blit(divergence[1]);

    clear(pressure.first[1]);
    pressureProgram.bind();
    gl.uniform2f(pressureProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(pressureProgram.uniforms.uDivergence, divergence[2]);
    for (var i = 0; i < PRESSURE_ITERATIONS; i++) {
        gl.uniform1i(pressureProgram.uniforms.uPressure, pressure.first[2]);
        blit(pressure.second[1]);
        pressure.swap();
    }

    gradienSubtractProgram.bind();
    gl.uniform2f(gradienSubtractProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
    gl.uniform1i(gradienSubtractProgram.uniforms.uPressure, pressure.first[2]);
    gl.uniform1i(gradienSubtractProgram.uniforms.uVelocity, velocity.first[2]);
    blit(velocity.second[1]);
    velocity.swap();

    gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
    displayProgram.bind();
    gl.uniform1i(displayProgram.uniforms.uTexture, density.first[2]);
    blit(null);

    requestAnimationFrame(Update);
}

function splat(x, y, dx, dy, color) {
    splatProgram.bind();
    gl.uniform1i(splatProgram.uniforms.uTarget, velocity.first[2]);
    gl.uniform1f(splatProgram.uniforms.aspectRatio, canvas.width / canvas.height);
    gl.uniform2f(splatProgram.uniforms.point, x / canvas.width, 1.0 - y / canvas.height);
    gl.uniform3f(splatProgram.uniforms.color, dx, -dy, 1.0);
    gl.uniform1f(splatProgram.uniforms.radius, SPLAT_RADIUS);
    blit(velocity.second[1]);
    velocity.swap();

    gl.uniform1i(splatProgram.uniforms.uTarget, density.first[2]);
    gl.uniform3f(splatProgram.uniforms.color, color[0] * 0.3, color[1] * 0.3, color[2] * 0.3);
    blit(density.second[1]);
    density.swap();
}

function resizeCanvas() {
    if (canvas.width != canvas.clientWidth || canvas.height != canvas.clientHeight) {
        canvas.width = canvas.clientWidth;
        canvas.height = canvas.clientHeight;
        initFramebuffers();
    }
}

canvas.addEventListener('mousemove', function (e) {
    pointers[0].moved = pointers[0].down;
    pointers[0].dx = (e.offsetX - pointers[0].x) * 10.0;
    pointers[0].dy = (e.offsetY - pointers[0].y) * 10.0;
    pointers[0].x = e.offsetX;
    pointers[0].y = e.offsetY;
	pointers[0].down = true;
});

canvas.addEventListener('touchmove', function (e) {
    e.preventDefault();
    var touches = e.targetTouches;
    for (var i = 0; i < e.touches.length; i++) {
        var pointer = pointers[i];
        pointer.moved = pointer.down;
        pointer.dx = (touches[i].pageX - pointer.x) * 10.0;
        pointer.dy = (touches[i].pageY - pointer.y) * 10.0;
        pointer.x = touches[i].pageX;
        pointer.y = touches[i].pageY;
    }
}, false);

canvas.addEventListener('mousedown', function () {
    pointers[0].down = true;
    pointers[0].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
});

canvas.addEventListener('touchstart', function (e) {
    var touches = e.targetTouches;
    for (var i = 0; i < touches.length; i++) {
        if (i >= pointers.length) pointers.push(new pointerPrototype());

        pointers[i].id = touches[i].identifier;
        pointers[i].down = true;
        pointers[i].x = touches[i].pageX;
        pointers[i].y = touches[i].pageY;
        pointers[i].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
    }
});

window.addEventListener('mouseup', function () {
    pointers[0].down = true;
});

window.addEventListener('touchend', function (e) {
    var touches = e.changedTouches;
    for (var i = 0; i < touches.length; i++) {
        for (var j = 0; j < pointers.length; j++) {
            if (touches[i].identifier == pointers[j].id) pointers[j].down = false;
        }
    }
});
```

## Getting Started

Please find below the definitions I have understood so far about the JavaScript code

### Breakdown the code
```
    var canvas = document.getElementsByTagName('canvas')[0];
    canvas.width = canvas.clientWidth;
    canvas.height = canvas.clientHeight;
    
    var params = { alpha: false, depth: false, stencil: false, antialias: false };
    var gl = canvas.getContext('webgl2', params);
    var isWebGL2 = !!gl;
    if (!isWebGL2) {
        gl = canvas.getContext('webgl', params) || canvas.getContext('experimental-webgl', params);
    }
    gl.clearColor(0.0, 0.0, 0.0, 1.0);

* var canvas = document.getElementsByTagName('canvas')[0];: Fetches the first canvas element in the HTML document.

* canvas.width = canvas.clientWidth; and canvas.height = canvas.clientHeight;: Sets the canvas dimensions to match the client dimensions, ensuring it fills the available space.

* var params = { alpha: false, depth: false, stencil: false, antialias: false };: Defines parameters for WebGL context creation, including options like alpha, depth, stencil, and antialiasing.

* var gl = canvas.getContext('webgl2', params);: Tries to create a WebGL2 context with the specified parameters. If WebGL2 is not supported, it falls back to WebGL or experimental WebGL.

* gl.clearColor(0.0, 0.0, 0.0, 1.0);: Sets the clear color for the WebGL context to black.

    var halfFloat = gl.getExtension('OES_texture_half_float');
    var support_linear_float = gl.getExtension('OES_texture_half_float_linear');
    if (isWebGL2) {
        gl.getExtension('EXT_color_buffer_float');
        support_linear_float = gl.getExtension('OES_texture_float_linear');
    }
    
    var TEXTURE_DOWNSAMPLE = 1;
    var DENSITY_DISSIPATION = 0.98;
    var VELOCITY_DISSIPATION = 0.99;
    var SPLAT_RADIUS = 0.005;
    var CURL = 30;
    var PRESSURE_ITERATIONS = 25;
    
    var GLProgram = function () {
        function GLProgram(vertexShader, fragmentShader) {
            _classCallCheck(this, GLProgram);
    
            this.uniforms = {};
            this.program = gl.createProgram();
    
            gl.attachShader(this.program, vertexShader);
            gl.attachShader(this.program, fragmentShader);
            gl.linkProgram(this.program);
    
            if (!gl.getProgramParameter(this.program, gl.LINK_STATUS)) throw gl.getProgramInfoLog(this.program);
    
            var uniformCount = gl.getProgramParameter(this.program, gl.ACTIVE_UNIFORMS);
            for (var i = 0; i < uniformCount; i++) {
                var uniformName = gl.getActiveUniform(this.program, i).name;
                this.uniforms[uniformName] = gl.getUniformLocation(this.program, uniformName);
            }
        }
    
        GLProgram.prototype.bind = function bind() {
            gl.useProgram(this.program);
        };
    
        return GLProgram;
    }();
```
* The code initializes WebGL extensions (halfFloat and support_linear_float) to enhance WebGL capabilities related to texture handling.

* It checks if WebGL2 is supported and enables additional extensions (EXT_color_buffer_float and OES_texture_float_linear) accordingly.

* Constants like TEXTURE_DOWNSAMPLE, DENSITY_DISSIPATION, etc., are defined to control simulation parameters.

* The GLProgram class is defined to manage WebGL programs. It handles program creation, shader attachment, program linking, and retrieval of uniform locations for setting values during rendering.

### Shader
```
    var baseVertexShader = compileShader(gl.VERTEX_SHADER, `
        precision highp float;
        precision mediump sampler2D;
    
        attribute vec2 aPosition;
        varying vec2 vUv;
        varying vec2 vL;
        varying vec2 vR;
        varying vec2 vT;
        varying vec2 vB;
        uniform vec2 texelSize;
    
        void main () {
            vUv = aPosition * 0.5 + 0.5;
            vL = vUv - vec2(texelSize.x, 0.0);
            vR = vUv + vec2(texelSize.x, 0.0);
            vT = vUv + vec2(0.0, texelSize.y);
            vB = vUv - vec2(0.0, texelSize.y);
            gl_Position = vec4(aPosition, 0.0, 1.0);
        }
    `);
```
* This code defines a vertex shader written in GLSL.

* It sets precision for floating-point values and texture sampling.

* Declares an attribute aPosition for vertex positions and varying variables (vUv, vL, vR, vT, vB) for texture coordinates and their neighbors.

* Calculates texture coordinates based on texelSize and sets the vertex position in clip space.

And so on for rest of the shaders as each shader serves a specific purpose in WebGL rendering, such as vertex transformations, texture display, and color splatting.
```
    var blit = function () {
        gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, -1, 1, 1, 1, 1, -1]), gl.STATIC_DRAW);
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, gl.createBuffer());
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array([0, 1, 2, 0, 2, 3]), gl.STATIC_DRAW);
        gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
        gl.enableVertexAttribArray(0);
    
        return function (destination) {
            gl.bindFramebuffer(gl.FRAMEBUFFER, destination);
            gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_SHORT, 0);
        };
    }();
    
    function clear(target) {
        gl.bindFramebuffer(gl.FRAMEBUFFER, target);
        gl.clear(gl.COLOR_BUFFER_BIT);
    }
```
* blit is a function that initializes and returns another function responsible for blitting (copying) content to a destination framebuffer.

* Inside blit, it sets up buffers for vertex positions and element indices to draw a full-screen quad.

* The clear function is used to clear the color buffer of a specified target framebuffer.
```
    function createDoubleFBO(texId, w, h, internalFormat, format, type, param) {
        var fbo1 = createFBO(texId, w, h, internalFormat, format, type, param);
        var fbo2 = createFBO(texId + 1, w, h, internalFormat, format, type, param);
    
        return {
            get first() {
                return fbo1;
            },
            get second() {
                return fbo2;
            },
            swap: function swap() {
                var temp = fbo1;
                fbo1 = fbo2;
                fbo2 = temp;
            }
        };
    }
    
    var textureWidth = undefined;
    var textureHeight = undefined;
    var density = undefined;
    var velocity = undefined;
    var divergence = undefined;
    var curl = undefined;
    var pressure = undefined;
    
    function initFramebuffers() {
        textureWidth = gl.drawingBufferWidth >> TEXTURE_DOWNSAMPLE;
        textureHeight = gl.drawingBufferHeight >> TEXTURE_DOWNSAMPLE;
    
        var internalFormat = isWebGL2 ? gl.RGBA16F : gl.RGBA;
        var internalFormatRG = isWebGL2 ? gl.RG16F : gl.RGBA;
        var formatRG = isWebGL2 ? gl.RG : gl.RGBA;
        var texType = isWebGL2 ? gl.HALF_FLOAT : halfFloat.HALF_FLOAT_OES;
    
        density = createDoubleFBO(0, textureWidth, textureHeight, internalFormat, gl.RGBA, texType, support_linear_float ? gl.LINEAR : gl.NEAREST);
        velocity = createDoubleFBO(2, textureWidth, textureHeight, internalFormatRG, formatRG, texType, support_linear_float ? gl.LINEAR : gl.NEAREST);
        divergence = createFBO(4, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
        curl = createFBO(5, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
        pressure = createDoubleFBO(6, textureWidth, textureHeight, internalFormatRG, formatRG, texType, gl.NEAREST);
    }
    
    initFramebuffers();
    
    var displayProgram = new GLProgram(baseVertexShader, displayShader);
    var splatProgram = new GLProgram(baseVertexShader, splatShader);
    var advectionProgram = new GLProgram(baseVertexShader, support_linear_float ? advectionShader : advectionManualFilteringShader);
    var divergenceProgram = new GLProgram(baseVertexShader, divergenceShader);
    var curlProgram = new GLProgram(baseVertexShader, curlShader);
    var vorticityProgram = new GLProgram(baseVertexShader, vorticityShader);
    var pressureProgram = new GLProgram(baseVertexShader, pressureShader);
    var gradienSubtractProgram = new GLProgram(baseVertexShader, gradientSubtractShader);
    
    function pointerPrototype() {
        this.id = -1;
        this.x = 0;
        this.y = 0;
        this.dx = 0;
        this.dy = 0;
        this.down = false;
        this.moved = false;
        this.color = [30, 0, 300];
    }
    
    var pointers = [];
    pointers.push(new pointerPrototype());
    
    for (var i = 0; i < 10; i++) {
        var color = [Math.random() * 10, Math.random() * 10, Math.random() * 10];
        var x = canvas.width * Math.random();
        var y = canvas.height * Math.random();
        var dx = 1000 * (Math.random() - 0.5);
        var dy = 1000 * (Math.random() - 0.5);
        splat(x, y, dx, dy, color);
    }
```
* The createDoubleFBO function is used to create double framebuffer objects (FBOs) for rendering, allowing for efficient swapping between two FBOs.

* The initFramebuffers function initializes various framebuffers (FBOs) for simulation, including double FBOs for density, velocity, and pressure, as well as single FBOs for divergence and curl.

* GL programs are created using GLProgram for different shaders used in the simulation.

* Pointer objects are initialized using a prototype for handling user input (e.g., mouse interactions).

* Random splats are generated on the canvas to initialize the simulation with initial conditions.
```
    canvas.addEventListener('mousemove', function (e) {
        pointers[0].moved = pointers[0].down;
        pointers[0].dx = (e.offsetX - pointers[0].x) * 10.0;
        pointers[0].dy = (e.offsetY - pointers[0].y) * 10.0;
        pointers[0].x = e.offsetX;
        pointers[0].y = e.offsetY;
     pointers[0].down = true;
    });
    
    canvas.addEventListener('touchmove', function (e) {
        e.preventDefault();
        var touches = e.targetTouches;
        for (var i = 0; i < e.touches.length; i++) {
            var pointer = pointers[i];
            pointer.moved = pointer.down;
            pointer.dx = (touches[i].pageX - pointer.x) * 10.0;
            pointer.dy = (touches[i].pageY - pointer.y) * 10.0;
            pointer.x = touches[i].pageX;
            pointer.y = touches[i].pageY;
        }
    }, false);
    
    canvas.addEventListener('mousedown', function () {
        pointers[0].down = true;
        pointers[0].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
    });
    
    canvas.addEventListener('touchstart', function (e) {
        var touches = e.targetTouches;
        for (var i = 0; i < touches.length; i++) {
            if (i >= pointers.length) pointers.push(new pointerPrototype());
    
            pointers[i].id = touches[i].identifier;
            pointers[i].down = true;
            pointers[i].x = touches[i].pageX;
            pointers[i].y = touches[i].pageY;
            pointers[i].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
        }
    });
    
    window.addEventListener('mouseup', function () {
        pointers[0].down = true;
    });
    
    window.addEventListener('touchend', function (e) {
        var touches = e.changedTouches;
        for (var i = 0; i < touches.length; i++) {
            for (var j = 0; j < pointers.length; j++) {
                if (touches[i].identifier == pointers[j].id) pointers[j].down = false;
            }
        }
    });
```
* The code sets up event listeners for mouse and touch interactions on the canvas.

* For mouse movement (mousemove), it updates the properties of the first pointer (pointers[0]) based on the mouse's position and movement.

* For touch movement (touchmove), it handles multiple touches by updating properties for each pointer accordingly.

* Mouse button press (mousedown) and touch start (touchstart) events update the pointer's down state and color.

* Mouse button release (mouseup) and touch end (touchend) events update the pointer's down state to false, indicating the release of interaction.


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