WebGL-Fluid-Simulation/script.js

'use strict';

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

let config = {
    SIM_RESOLUTION: 128,
    DYE_RESOLUTION: 512,
    DENSITY_DISSIPATION: 0.97,
    VELOCITY_DISSIPATION: 0.98,
    PRESSURE_DISSIPATION: 0.8,
    PRESSURE_ITERATIONS: 20,
    CURL: 30,
    SPLAT_RADIUS: 0.5,
    SHADING: true,
    COLORFUL: true,
    PAUSED: false,
    BACK_COLOR: { r: 0, g: 0, b: 0 },
    TRANSPARENT: false
}

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];
}

let pointers = [];
let splatStack = [];
pointers.push(new pointerPrototype());

const { gl, ext } = getWebGLContext(canvas);

if (isMobile())
    config.SHADING = false;
if (!ext.supportLinearFiltering)
    config.SHADING = false;

startGUI();

function getWebGLContext (canvas) {
    const params = { alpha: true, depth: false, stencil: false, antialias: false, preserveDrawingBuffer: false };

    let gl = canvas.getContext('webgl2', params);
    const isWebGL2 = !!gl;
    if (!isWebGL2)
        gl = canvas.getContext('webgl', params) || canvas.getContext('experimental-webgl', params);

    let halfFloat;
    let supportLinearFiltering;
    if (isWebGL2) {
        gl.getExtension('EXT_color_buffer_float');
        supportLinearFiltering = gl.getExtension('OES_texture_float_linear');
    } else {
        halfFloat = gl.getExtension('OES_texture_half_float');
        supportLinearFiltering = gl.getExtension('OES_texture_half_float_linear');
    }

    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    const halfFloatTexType = isWebGL2 ? gl.HALF_FLOAT : halfFloat.HALF_FLOAT_OES;
    let formatRGBA;
    let formatRG;
    let formatR;

    if (isWebGL2)
    {
        formatRGBA = getSupportedFormat(gl, gl.RGBA16F, gl.RGBA, halfFloatTexType);
        formatRG = getSupportedFormat(gl, gl.RG16F, gl.RG, halfFloatTexType);
        formatR = getSupportedFormat(gl, gl.R16F, gl.RED, halfFloatTexType);
    }
    else
    {
        formatRGBA = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
        formatRG = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
        formatR = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
    }

    if (formatRGBA == null)
        ga('send', 'event', isWebGL2 ? 'webgl2' : 'webgl', 'not supported');
    else
        ga('send', 'event', isWebGL2 ? 'webgl2' : 'webgl', 'supported');

    return {
        gl,
        ext: {
            formatRGBA,
            formatRG,
            formatR,
            halfFloatTexType,
            supportLinearFiltering
        }
    };
}

function getSupportedFormat (gl, internalFormat, format, type)
{
    if (!supportRenderTextureFormat(gl, internalFormat, format, type))
    {
        switch (internalFormat)
        {
            case gl.R16F:
                return getSupportedFormat(gl, gl.RG16F, gl.RG, type);
            case gl.RG16F:
                return getSupportedFormat(gl, gl.RGBA16F, gl.RGBA, type);
            default:
                return null;
        }
    }

    return {
        internalFormat,
        format
    }
}

function supportRenderTextureFormat (gl, internalFormat, format, type) {
    let texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    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, 4, 4, 0, format, type, null);

    let fbo = gl.createFramebuffer();
    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);

    const status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
    if (status != gl.FRAMEBUFFER_COMPLETE)
        return false;
    return true;
}

function startGUI () {
    var gui = new dat.GUI({ width: 300 });
    gui.add(config, 'SIM_RESOLUTION', { '32': 32, '64': 64, '128': 128, '256': 256 }).name('sim resolution').onFinishChange(initFramebuffers);
    gui.add(config, 'DYE_RESOLUTION', { '128': 128, '256': 256, '512': 512, '1024': 1024 }).name('dye resolution').onFinishChange(initFramebuffers);
    gui.add(config, 'DENSITY_DISSIPATION', 0.9, 1.0).name('density diffusion');
    gui.add(config, 'VELOCITY_DISSIPATION', 0.9, 1.0).name('velocity diffusion');
    gui.add(config, 'PRESSURE_DISSIPATION', 0.0, 1.0).name('pressure diffusion');
    // gui.add(config, 'PRESSURE_ITERATIONS', 1, 60).name('iterations');
    gui.add(config, 'CURL', 0, 50).name('vorticity').step(1);
    gui.add(config, 'SPLAT_RADIUS', 0.01, 1.0).name('splat radius');
    gui.add(config, 'SHADING').name('shading');
    gui.add(config, 'COLORFUL').name('colorful');
    gui.add(config, 'PAUSED').name('paused').listen();

    gui.add({ fun: () => {
        splatStack.push(parseInt(Math.random() * 20) + 5);
    } }, 'fun').name('Random splats');

    let captureFolder = gui.addFolder('Capture');
    captureFolder.addColor(config, 'BACK_COLOR').name('background color');
    captureFolder.add(config, 'TRANSPARENT').name('transparent');
    captureFolder.add({ fun: captureScreenshot }, 'fun').name('take screenshot');

    let github = gui.add({ fun : () => {
        window.open('https://github.com/PavelDoGreat/WebGL-Fluid-Simulation');
        ga('send', 'event', 'link button', 'github');
    } }, 'fun').name('Github');
    github.__li.className = 'cr function bigFont';
    github.__li.style.borderLeft = '3px solid #8C8C8C';
    let githubIcon = document.createElement('span');
    github.domElement.parentElement.appendChild(githubIcon);
    githubIcon.className = 'icon github';

    let twitter = gui.add({ fun : () => {
        window.open('https://twitter.com/PavelDoGreat');
        ga('send', 'event', 'link button', 'twitter');
    } }, 'fun').name('Twitter');
    twitter.__li.className = 'cr function bigFont';
    twitter.__li.style.borderLeft = '3px solid #8C8C8C';
    let twitterIcon = document.createElement('span');
    twitter.domElement.parentElement.appendChild(twitterIcon);
    twitterIcon.className = 'icon twitter';

    let discord = gui.add({ fun : () => {
        window.open('https://discordapp.com/invite/CeqZDDE');
        ga('send', 'event', 'link button', 'discord');
    } }, 'fun').name('Discord');
    discord.__li.className = 'cr function bigFont';
    discord.__li.style.borderLeft = '3px solid #8C8C8C';
    let discordIcon = document.createElement('span');
    discord.domElement.parentElement.appendChild(discordIcon);
    discordIcon.className = 'icon discord';

    let app = gui.add({ fun : () => {
        window.open('http://onelink.to/5b58bn');
        ga('send', 'event', 'link button', 'app');
    } }, 'fun').name('Check out new improved version');
    app.__li.className = 'cr function appBigFont';
    app.__li.style.borderLeft = '3px solid #00FF7F';
    let appIcon = document.createElement('span');
    app.domElement.parentElement.appendChild(appIcon);
    appIcon.className = 'icon app';

    if (isMobile())
        gui.close();
}

function captureScreenshot () {
    colorProgram.bind();
    gl.uniform4f(colorProgram.uniforms.color, 0, 0, 0, 1);
    blit(density.write.fbo);

    render(density.write.fbo);
    gl.bindFramebuffer(gl.FRAMEBUFFER, density.write.fbo);

    let length = dyeWidth * dyeHeight * 4;
    let pixels = new Float32Array(length);
    gl.readPixels(0, 0, dyeWidth, dyeHeight, gl.RGBA, gl.FLOAT, pixels);

    let newPixels = new Uint8Array(length);

    let id = 0;
    for (let i = dyeHeight - 1; i >= 0; i--) {
        for (let j = 0; j < dyeWidth; j++) {
            let nid = i * dyeWidth * 4 + j * 4;
            newPixels[nid + 0] = clamp01(pixels[id + 0]) * 255;
            newPixels[nid + 1] = clamp01(pixels[id + 1]) * 255;
            newPixels[nid + 2] = clamp01(pixels[id + 2]) * 255;
            newPixels[nid + 3] = clamp01(pixels[id + 3]) * 255;
            id += 4;
        }
    }

    let captureCanvas = document.createElement('canvas');
    let ctx = captureCanvas.getContext('2d');
    captureCanvas.width = dyeWidth;
    captureCanvas.height = dyeHeight;

    let imageData = ctx.createImageData(dyeWidth, dyeHeight);
    imageData.data.set(newPixels);
    ctx.putImageData(imageData, 0, 0);
    let datauri = captureCanvas.toDataURL();

    downloadURI("fluid.png", datauri);

    URL.revokeObjectURL(datauri);
}

function clamp01 (input) {
    return Math.min(Math.max(input, 0), 1);
}

function downloadURI (filename, uri) {
    let link = document.createElement("a");
    link.download = filename;
    link.href = uri;
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
}

function isMobile () {
    return /Mobi|Android/i.test(navigator.userAgent);
}

class GLProgram {
    constructor (vertexShader, fragmentShader) {
        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);

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

    bind () {
        gl.useProgram(this.program);
    }
}

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

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

    return shader;
};

const baseVertexShader = compileShader(gl.VERTEX_SHADER, `
    precision highp float;

    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);
    }
`);

const clearShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;
    precision mediump sampler2D;

    varying highp vec2 vUv;
    uniform sampler2D uTexture;
    uniform float value;

    void main () {
        gl_FragColor = value * texture2D(uTexture, vUv);
    }
`);

const colorShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;

    uniform vec4 color;

    void main () {
        gl_FragColor = color;
    }
`);

const backgroundShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTexture;
    uniform float aspectRatio;

    #define SCALE 25.0

    void main () {
        vec2 uv = floor(vUv * SCALE * vec2(aspectRatio, 1.0));
        float v = mod(uv.x + uv.y, 2.0);
        v = v * 0.1 + 0.8;
        gl_FragColor = vec4(vec3(v), 1.0);
    }
`);

const displayShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTexture;

    void main () {
        vec3 C = texture2D(uTexture, vUv).rgb;
        float a = max(C.r, max(C.g, C.b));
        gl_FragColor = vec4(C, a);
    }
`);

const displayShadingShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uTexture;
    uniform vec2 texelSize;

    void main () {
        vec3 L = texture2D(uTexture, vL).rgb;
        vec3 R = texture2D(uTexture, vR).rgb;
        vec3 T = texture2D(uTexture, vT).rgb;
        vec3 B = texture2D(uTexture, vB).rgb;
        vec3 C = texture2D(uTexture, vUv).rgb;

        float dx = length(R) - length(L);
        float dy = length(T) - length(B);

        vec3 n = normalize(vec3(dx, dy, length(texelSize)));
        vec3 l = vec3(0.0, 0.0, 1.0);

        float diffuse = clamp(dot(n, l) + 0.7, 0.7, 1.0);
        C.rgb *= diffuse;

        float a = max(C.r, max(C.g, C.b));
        gl_FragColor = vec4(C, a);
    }
`);

const splatShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTarget;
    uniform float aspectRatio;
    uniform vec3 color;
    uniform vec2 point;
    uniform float radius;

    void main () {
        vec2 p = vUv - point.xy;
        p.x *= aspectRatio;
        vec3 splat = exp(-dot(p, p) / radius) * color;
        vec3 base = texture2D(uTarget, vUv).xyz;
        gl_FragColor = vec4(base + splat, 1.0);
    }
`);

const advectionManualFilteringShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    uniform sampler2D uVelocity;
    uniform sampler2D uSource;
    uniform vec2 texelSize;
    uniform vec2 dyeTexelSize;
    uniform float dt;
    uniform float dissipation;

    vec4 bilerp (sampler2D sam, vec2 uv, vec2 tsize) {
        vec2 st = uv / tsize - 0.5;

        vec2 iuv = floor(st);
        vec2 fuv = fract(st);

        vec4 a = texture2D(sam, (iuv + vec2(0.5, 0.5)) * tsize);
        vec4 b = texture2D(sam, (iuv + vec2(1.5, 0.5)) * tsize);
        vec4 c = texture2D(sam, (iuv + vec2(0.5, 1.5)) * tsize);
        vec4 d = texture2D(sam, (iuv + vec2(1.5, 1.5)) * tsize);

        return mix(mix(a, b, fuv.x), mix(c, d, fuv.x), fuv.y);
    }

    void main () {
        vec2 coord = vUv - dt * bilerp(uVelocity, vUv, texelSize).xy * texelSize;
        gl_FragColor = dissipation * bilerp(uSource, coord, dyeTexelSize);
        gl_FragColor.a = 1.0;
    }
`);

const advectionShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    uniform sampler2D uVelocity;
    uniform sampler2D uSource;
    uniform vec2 texelSize;
    uniform float dt;
    uniform float dissipation;

    void main () {
        vec2 coord = vUv - dt * texture2D(uVelocity, vUv).xy * texelSize;
        gl_FragColor = dissipation * texture2D(uSource, coord);
        gl_FragColor.a = 1.0;
    }
`);

const divergenceShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;
    precision mediump sampler2D;

    varying highp vec2 vUv;
    varying highp vec2 vL;
    varying highp vec2 vR;
    varying highp vec2 vT;
    varying highp vec2 vB;
    uniform sampler2D uVelocity;

    void main () {
        float L = texture2D(uVelocity, vL).x;
        float R = texture2D(uVelocity, vR).x;
        float T = texture2D(uVelocity, vT).y;
        float B = texture2D(uVelocity, vB).y;

        vec2 C = texture2D(uVelocity, vUv).xy;
        if (vL.x < 0.0) { L = -C.x; }
        if (vR.x > 1.0) { R = -C.x; }
        if (vT.y > 1.0) { T = -C.y; }
        if (vB.y < 0.0) { B = -C.y; }

        float div = 0.5 * (R - L + T - B);
        gl_FragColor = vec4(div, 0.0, 0.0, 1.0);
    }
`);

const curlShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;
    precision mediump sampler2D;

    varying highp vec2 vUv;
    varying highp vec2 vL;
    varying highp vec2 vR;
    varying highp vec2 vT;
    varying highp vec2 vB;
    uniform sampler2D uVelocity;

    void main () {
        float L = texture2D(uVelocity, vL).y;
        float R = texture2D(uVelocity, vR).y;
        float T = texture2D(uVelocity, vT).x;
        float B = texture2D(uVelocity, vB).x;
        float vorticity = R - L - T + B;
        gl_FragColor = vec4(0.5 * vorticity, 0.0, 0.0, 1.0);
    }
`);

const vorticityShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision highp sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uVelocity;
    uniform sampler2D uCurl;
    uniform float curl;
    uniform float dt;

    void main () {
        float L = texture2D(uCurl, vL).x;
        float R = texture2D(uCurl, vR).x;
        float T = texture2D(uCurl, vT).x;
        float B = texture2D(uCurl, vB).x;
        float C = texture2D(uCurl, vUv).x;

        vec2 force = 0.5 * vec2(abs(T) - abs(B), abs(R) - abs(L));
        force /= length(force) + 0.0001;
        force *= curl * C;
        force.y *= -1.0;

        vec2 vel = texture2D(uVelocity, vUv).xy;
        gl_FragColor = vec4(vel + force * dt, 0.0, 1.0);
    }
`);

const pressureShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;
    precision mediump sampler2D;

    varying highp vec2 vUv;
    varying highp vec2 vL;
    varying highp vec2 vR;
    varying highp vec2 vT;
    varying highp vec2 vB;
    uniform sampler2D uPressure;
    uniform sampler2D uDivergence;

    vec2 boundary (vec2 uv) {
        return uv;
        // uncomment if you use wrap or repeat texture mode
        // uv = min(max(uv, 0.0), 1.0);
        // return uv;
    }

    void main () {
        float L = texture2D(uPressure, boundary(vL)).x;
        float R = texture2D(uPressure, boundary(vR)).x;
        float T = texture2D(uPressure, boundary(vT)).x;
        float B = texture2D(uPressure, boundary(vB)).x;
        float C = texture2D(uPressure, vUv).x;
        float divergence = texture2D(uDivergence, vUv).x;
        float pressure = (L + R + B + T - divergence) * 0.25;
        gl_FragColor = vec4(pressure, 0.0, 0.0, 1.0);
    }
`);

const gradientSubtractShader = compileShader(gl.FRAGMENT_SHADER, `
    precision mediump float;
    precision mediump sampler2D;

    varying highp vec2 vUv;
    varying highp vec2 vL;
    varying highp vec2 vR;
    varying highp vec2 vT;
    varying highp vec2 vB;
    uniform sampler2D uPressure;
    uniform sampler2D uVelocity;

    vec2 boundary (vec2 uv) {
        return uv;
        // uv = min(max(uv, 0.0), 1.0);
        // return uv;
    }

    void main () {
        float L = texture2D(uPressure, boundary(vL)).x;
        float R = texture2D(uPressure, boundary(vR)).x;
        float T = texture2D(uPressure, boundary(vT)).x;
        float B = texture2D(uPressure, boundary(vB)).x;
        vec2 velocity = texture2D(uVelocity, vUv).xy;
        velocity.xy -= vec2(R - L, T - B);
        gl_FragColor = vec4(velocity, 0.0, 1.0);
    }
`);

const blit = (() => {
    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 (destination) => {
        gl.bindFramebuffer(gl.FRAMEBUFFER, destination);
        gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_SHORT, 0);
    }
})();

let simWidth;
let simHeight;
let dyeWidth;
let dyeHeight;
let density;
let velocity;
let divergence;
let curl;
let pressure;

const clearProgram           = new GLProgram(baseVertexShader, clearShader);
const colorProgram           = new GLProgram(baseVertexShader, colorShader);
const backgroundProgram      = new GLProgram(baseVertexShader, backgroundShader);
const displayProgram         = new GLProgram(baseVertexShader, displayShader);
const displayShadingProgram  = new GLProgram(baseVertexShader, displayShadingShader);
const splatProgram           = new GLProgram(baseVertexShader, splatShader);
const advectionProgram       = new GLProgram(baseVertexShader, ext.supportLinearFiltering ? advectionShader : advectionManualFilteringShader);
const divergenceProgram      = new GLProgram(baseVertexShader, divergenceShader);
const curlProgram            = new GLProgram(baseVertexShader, curlShader);
const vorticityProgram       = new GLProgram(baseVertexShader, vorticityShader);
const pressureProgram        = new GLProgram(baseVertexShader, pressureShader);
const gradienSubtractProgram = new GLProgram(baseVertexShader, gradientSubtractShader);

function initFramebuffers () {
    let simRes = getResolution(config.SIM_RESOLUTION);
    let dyeRes = getResolution(config.DYE_RESOLUTION);

    simWidth  = simRes.width;
    simHeight = simRes.height;
    dyeWidth  = dyeRes.width;
    dyeHeight = dyeRes.height;

    const texType = ext.halfFloatTexType;
    const rgba    = ext.formatRGBA;
    const rg      = ext.formatRG;
    const r       = ext.formatR;

    density    = createDoubleFBO(2, dyeWidth, dyeHeight, rgba.internalFormat, rgba.format, texType, ext.supportLinearFiltering ? gl.LINEAR : gl.NEAREST);
    velocity   = createDoubleFBO(0, simWidth, simHeight, rg.internalFormat, rg.format, texType, ext.supportLinearFiltering ? gl.LINEAR : gl.NEAREST);
    divergence = createFBO      (4, simWidth, simHeight, r.internalFormat, r.format, texType, gl.NEAREST);
    curl       = createFBO      (5, simWidth, simHeight, r.internalFormat, r.format, texType, gl.NEAREST);
    pressure   = createDoubleFBO(6, simWidth, simHeight, r.internalFormat, r.format, texType, gl.NEAREST);
}

function getResolution (resolution) {
    let aspectRatio = gl.drawingBufferWidth / gl.drawingBufferHeight;
    if (aspectRatio < 1)
        aspectRatio = 1.0 / aspectRatio;

    let max = Math.round(resolution * aspectRatio);
    let min = Math.round(resolution);

    if (gl.drawingBufferWidth > gl.drawingBufferHeight)
        return { width: max, height: min };
    else
        return { width: min, height: max };
}

function createFBO (texId, w, h, internalFormat, format, type, param) {
    gl.activeTexture(gl.TEXTURE0 + texId);
    let 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);

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

    return {
        get read () {
            return fbo1;
        },
        get write () {
            return fbo2;
        },
        swap () {
            let temp = fbo1;
            fbo1 = fbo2;
            fbo2 = temp;
        }
    }
}

initFramebuffers();
multipleSplats(parseInt(Math.random() * 20) + 5);

let lastColorChangeTime = Date.now();

update();

function update () {
    resizeCanvas();
    input();
    if (!config.PAUSED)
        step(0.016);
    render(null);
    requestAnimationFrame(update);
}

function input () {
    if (splatStack.length > 0)
        multipleSplats(splatStack.pop());

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

    if (!config.COLORFUL)
        return;

    if (lastColorChangeTime + 100 < Date.now())
    {
        lastColorChangeTime = Date.now();
        for (let i = 0; i < pointers.length; i++) {
            const p = pointers[i];
            p.color = generateColor();
        }
    }
}

function step (dt) {
    gl.disable(gl.BLEND);
    gl.viewport(0, 0, simWidth, simHeight);

    curlProgram.bind();
    gl.uniform2f(curlProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(curlProgram.uniforms.uVelocity, velocity.read.texId);
    blit(curl.fbo);

    vorticityProgram.bind();
    gl.uniform2f(vorticityProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(vorticityProgram.uniforms.uVelocity, velocity.read.texId);
    gl.uniform1i(vorticityProgram.uniforms.uCurl, curl.texId);
    gl.uniform1f(vorticityProgram.uniforms.curl, config.CURL);
    gl.uniform1f(vorticityProgram.uniforms.dt, dt);
    blit(velocity.write.fbo);
    velocity.swap();

    divergenceProgram.bind();
    gl.uniform2f(divergenceProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(divergenceProgram.uniforms.uVelocity, velocity.read.texId);
    blit(divergence.fbo);

    clearProgram.bind();
    let pressureTexId = pressure.read.texId;
    gl.activeTexture(gl.TEXTURE0 + pressureTexId);
    gl.bindTexture(gl.TEXTURE_2D, pressure.read.texture);
    gl.uniform1i(clearProgram.uniforms.uTexture, pressureTexId);
    gl.uniform1f(clearProgram.uniforms.value, config.PRESSURE_DISSIPATION);
    blit(pressure.write.fbo);
    pressure.swap();

    pressureProgram.bind();
    gl.uniform2f(pressureProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(pressureProgram.uniforms.uDivergence, divergence.texId);
    pressureTexId = pressure.read.texId;
    gl.uniform1i(pressureProgram.uniforms.uPressure, pressureTexId);
    gl.activeTexture(gl.TEXTURE0 + pressureTexId);
    for (let i = 0; i < config.PRESSURE_ITERATIONS; i++) {
        gl.bindTexture(gl.TEXTURE_2D, pressure.read.texture);
        blit(pressure.write.fbo);
        pressure.swap();
    }

    gradienSubtractProgram.bind();
    gl.uniform2f(gradienSubtractProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(gradienSubtractProgram.uniforms.uPressure, pressure.read.texId);
    gl.uniform1i(gradienSubtractProgram.uniforms.uVelocity, velocity.read.texId);
    blit(velocity.write.fbo);
    velocity.swap();

    advectionProgram.bind();
    gl.uniform2f(advectionProgram.uniforms.texelSize, 1.0 / simWidth, 1.0 / simHeight);
    if (!ext.supportLinearFiltering)
        gl.uniform2f(advectionProgram.uniforms.dyeTexelSize, 1.0 / simWidth, 1.0 / simHeight);
    gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.read.texId);
    gl.uniform1i(advectionProgram.uniforms.uSource, velocity.read.texId);
    gl.uniform1f(advectionProgram.uniforms.dt, dt);
    gl.uniform1f(advectionProgram.uniforms.dissipation, config.VELOCITY_DISSIPATION);
    blit(velocity.write.fbo);
    velocity.swap();

    gl.viewport(0, 0, dyeWidth, dyeHeight);

    if (!ext.supportLinearFiltering)
        gl.uniform2f(advectionProgram.uniforms.dyeTexelSize, 1.0 / dyeWidth, 1.0 / dyeHeight);
    gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.read.texId);
    gl.uniform1i(advectionProgram.uniforms.uSource, density.read.texId);
    gl.uniform1f(advectionProgram.uniforms.dissipation, config.DENSITY_DISSIPATION);
    blit(density.write.fbo);
    density.swap();
}

function render (target) {
    if (target == null || !config.TRANSPARENT) {
        gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
        gl.enable(gl.BLEND);
    }
    else {
        gl.disable(gl.BLEND);
    }

    let width  = target == null ? gl.drawingBufferWidth : dyeWidth;
    let height = target == null ? gl.drawingBufferHeight : dyeHeight;

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

    if (!config.TRANSPARENT) {
        colorProgram.bind();
        let bc = config.BACK_COLOR;
        gl.uniform4f(colorProgram.uniforms.color, bc.r / 255, bc.g / 255, bc.b / 255, 1);
        blit(target);
    }

    if (target == null && config.TRANSPARENT) {
        backgroundProgram.bind();
        gl.uniform1f(backgroundProgram.uniforms.aspectRatio, canvas.width / canvas.height);
        blit(null);
    }

    if (config.SHADING) {
        displayShadingProgram.bind();
        gl.uniform2f(displayShadingProgram.uniforms.texelSize, 1.0 / width, 1.0 / height);
        gl.uniform1i(displayShadingProgram.uniforms.uTexture, density.read.texId);
    }
    else {
        displayProgram.bind();
        gl.uniform1i(displayProgram.uniforms.uTexture, density.read.texId);
    }

    blit(target);
}

function splat (x, y, dx, dy, color) {
    gl.viewport(0, 0, simWidth, simHeight);
    splatProgram.bind();
    gl.uniform1i(splatProgram.uniforms.uTarget, velocity.read.texId);
    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, config.SPLAT_RADIUS / 100.0);
    blit(velocity.write.fbo);
    velocity.swap();

    gl.viewport(0, 0, dyeWidth, dyeHeight);
    gl.uniform1i(splatProgram.uniforms.uTarget, density.read.texId);
    gl.uniform3f(splatProgram.uniforms.color, color.r, color.g, color.b);
    blit(density.write.fbo);
    density.swap();
}

function multipleSplats (amount) {
    for (let i = 0; i < amount; i++) {
        const color = generateColor();
        color.r *= 10.0;
        color.g *= 10.0;
        color.b *= 10.0;
        const x = canvas.width * Math.random();
        const y = canvas.height * Math.random();
        const dx = 1000 * (Math.random() - 0.5);
        const dy = 1000 * (Math.random() - 0.5);
        splat(x, y, dx, dy, color);
    }
}

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

canvas.addEventListener('mousemove', e => {
    pointers[0].moved = pointers[0].down;
    pointers[0].dx = (e.offsetX - pointers[0].x) * 5.0;
    pointers[0].dy = (e.offsetY - pointers[0].y) * 5.0;
    pointers[0].x = e.offsetX;
    pointers[0].y = e.offsetY;
});

canvas.addEventListener('touchmove', e => {
    e.preventDefault();
    const touches = e.targetTouches;
    for (let i = 0; i < touches.length; i++) {
        let pointer = pointers[i];
        pointer.moved = pointer.down;
        pointer.dx = (touches[i].pageX - pointer.x) * 8.0;
        pointer.dy = (touches[i].pageY - pointer.y) * 8.0;
        pointer.x = touches[i].pageX;
        pointer.y = touches[i].pageY;
    }
}, false);

canvas.addEventListener('mousedown', () => {
    pointers[0].down = true;
    pointers[0].color = generateColor();
});

canvas.addEventListener('touchstart', e => {
    e.preventDefault();
    const touches = e.targetTouches;
    for (let 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 = generateColor();
    }
});

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

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

window.addEventListener('keydown', e => {
    if (e.key === 'p')
        config.PAUSED = !config.PAUSED;
    if (e.key === ' ')
        splatStack.push(parseInt(Math.random() * 20) + 5);
});

function generateColor () {
    let c = HSVtoRGB(Math.random(), 1.0, 1.0);
    c.r *= 0.15;
    c.g *= 0.15;
    c.b *= 0.15;
    return c;
}

function HSVtoRGB (h, s, v) {
    let r, g, b, i, f, p, q, t;
    i = Math.floor(h * 6);
    f = h * 6 - i;
    p = v * (1 - s);
    q = v * (1 - f * s);
    t = v * (1 - (1 - f) * s);

    switch (i % 6) {
        case 0: r = v, g = t, b = p; break;
        case 1: r = q, g = v, b = p; break;
        case 2: r = p, g = v, b = t; break;
        case 3: r = p, g = q, b = v; break;
        case 4: r = t, g = p, b = v; break;
        case 5: r = v, g = p, b = q; break;
    }

    return {
        r,
        g,
        b
    };
}