WebGL Fluid Simulation / Jeremy Ashkenas

Jeremy Ashkenas

Used to work on @observablehq — still think it rocks. 🏍 🌎 👶

Workspace

Published

WebGL

Edited

Jan 30, 2018

4 forks

41 stars

ctx = {

const params = {alpha: false, depth: false, stencil: false, antialias: 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 supportLinearFloat;

if (isWebGL2) {

gl.getExtension('EXT_color_buffer_float');

supportLinearFloat = gl.getExtension('OES_texture_float_linear');

} else {

halfFloat = gl.getExtension('OES_texture_half_float');

supportLinearFloat = 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;

const internalFormat = isWebGL2 ? gl.RGBA16F : gl.RGBA;

let internalFormatRG = isWebGL2 ? gl.RG16F : gl.RGBA;

let formatRG = isWebGL2 ? gl.RG : gl.RGBA;

if (isWebGL2) {

if (!supportRenderTextureFormat(gl, internalFormatRG, formatRG, halfFloatTexType)) {

internalFormatRG = gl.RGBA16F;

formatRG = gl.RGBA;

}

return {

gl,

ext: {internalFormat, internalFormatRG, formatRG, halfFloatTexType, supportLinearFloat}

};

}

gl = ctx.gl

ext = ctx.ext

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);

return status == gl.FRAMEBUFFER_COMPLETE;

}

function randomSplats() {

splatStack.push(parseInt(Math.random() * 20) + 5);

}

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);

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);

return shader;

}

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);

}

clearShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

uniform sampler2D uTexture;

uniform float value;

void main () {

gl_FragColor = value * texture2D(uTexture, vUv);

}

displayShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

uniform sampler2D uTexture;

void main () {

gl_FragColor = texture2D(uTexture, vUv);

}

splatShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump 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);

}

advectionManualFilteringShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

uniform sampler2D uVelocity;

uniform sampler2D uSource;

uniform vec2 texelSize;

uniform float dt;

uniform float dissipation;

vec4 bilerp (in sampler2D sam, in vec2 p) {

vec4 st;

st.xy = floor(p - 0.5) + 0.5;

st.zw = st.xy + 1.0;

vec4 uv = st * texelSize.xyxy;

vec4 a = texture2D(sam, uv.xy);

vec4 b = texture2D(sam, uv.zy);

vec4 c = texture2D(sam, uv.xw);

vec4 d = texture2D(sam, uv.zw);

vec2 f = p - st.xy;

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

}

void main () {

vec2 coord = gl_FragCoord.xy - dt * texture2D(uVelocity, vUv).xy;

gl_FragColor = dissipation * bilerp(uSource, coord);

gl_FragColor.a = 1.0;

}

advectionShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump 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);

}

divergenceShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

varying vec2 vL;

varying vec2 vR;

varying vec2 vT;

varying vec2 vB;

uniform sampler2D uVelocity;

vec2 sampleVelocity (in vec2 uv) {

vec2 multiplier = vec2(1.0, 1.0);

if (uv.x < 0.0) { uv.x = 0.0; multiplier.x = -1.0; }

if (uv.x > 1.0) { uv.x = 1.0; multiplier.x = -1.0; }

if (uv.y < 0.0) { uv.y = 0.0; multiplier.y = -1.0; }

if (uv.y > 1.0) { uv.y = 1.0; multiplier.y = -1.0; }

return multiplier * texture2D(uVelocity, uv).xy;

}

void main () {

float L = sampleVelocity(vL).x;

float R = sampleVelocity(vR).x;

float T = sampleVelocity(vT).y;

float B = sampleVelocity(vB).y;

float div = 0.5 * (R - L + T - B);

gl_FragColor = vec4(div, 0.0, 0.0, 1.0);

}

curlShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

varying vec2 vL;

varying vec2 vR;

varying vec2 vT;

varying 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(vorticity, 0.0, 0.0, 1.0);

}

vorticityShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump 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).y;

float R = texture2D(uCurl, vR).y;

float T = texture2D(uCurl, vT).x;

float B = texture2D(uCurl, vB).x;

float C = texture2D(uCurl, vUv).x;

vec2 force = vec2(abs(T) - abs(B), abs(R) - abs(L));

force *= 1.0 / length(force + 0.00001) * curl * C;

vec2 vel = texture2D(uVelocity, vUv).xy;

gl_FragColor = vec4(vel + force * dt, 0.0, 1.0);

}

pressureShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

varying vec2 vL;

varying vec2 vR;

varying vec2 vT;

varying vec2 vB;

uniform sampler2D uPressure;

uniform sampler2D uDivergence;

vec2 boundary (in vec2 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;

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);

}

gradientSubtractShader = compileShader(gl.FRAGMENT_SHADER, `

precision highp float;

precision mediump sampler2D;

varying vec2 vUv;

varying vec2 vL;

varying vec2 vR;

varying vec2 vT;

varying vec2 vB;

uniform sampler2D uPressure;

uniform sampler2D uVelocity;

vec2 boundary (in vec2 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);

}

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 first () {

return fbo1;

get second () {

return fbo2;

swap () {

let temp = fbo1;

fbo1 = fbo2;

fbo2 = temp;

}

textureWidth = gl.drawingBufferWidth >> downsample

textureHeight = gl.drawingBufferHeight >> downsample

density = createDoubleFBO(0, textureWidth, textureHeight, ext.internalFormat, gl.RGBA, ext.halfFloatTexType, ext.supportLinearFloat ? gl.LINEAR : gl.NEAREST)

velocity = createDoubleFBO(2, textureWidth, textureHeight, ext.internalFormatRG, ext.formatRG, ext.halfFloatTexType, ext.supportLinearFloat ? gl.LINEAR : gl.NEAREST)

divergence = createFBO(4, textureWidth, textureHeight, ext.internalFormatRG, ext.formatRG, ext.halfFloatTexType, gl.NEAREST)

curl = createFBO(5, textureWidth, textureHeight, ext.internalFormatRG, ext.formatRG, ext.halfFloatTexType, gl.NEAREST)

pressure = createDoubleFBO(6, textureWidth, textureHeight, ext.internalFormatRG, ext.formatRG, ext.halfFloatTexType, gl.NEAREST)

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);

}

clearProgram = new GLProgram(baseVertexShader, clearShader)

displayProgram = new GLProgram(baseVertexShader, displayShader)

splatProgram = new GLProgram(baseVertexShader, splatShader)

advectionProgram = new GLProgram(baseVertexShader, ext.supportLinearFloat ? advectionShader : advectionManualFilteringShader)

divergenceProgram = new GLProgram(baseVertexShader, divergenceShader)

curlProgram = new GLProgram(baseVertexShader, curlShader)

vorticityProgram = new GLProgram(baseVertexShader, vorticityShader)

pressureProgram = new GLProgram(baseVertexShader, pressureShader)

gradienSubtractProgram = new GLProgram(baseVertexShader, gradientSubtractShader)

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, 0.01);

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 multipleSplats(amount) {

for (let i = 0; i < amount; i++) {

const color = [Math.random() * 10, Math.random() * 10, Math.random() * 10];

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);

}

mainLoop = {

let i = 0;

while (true) {

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

if (splatStack.length > 0) multipleSplats(splatStack.pop());

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, velocityDissipation);

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, densityDissipation);

blit(density.second[1]);

density.swap();

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, curlDegree);

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]);

clearProgram.bind();

let pressureTexId = pressure.first[2];

gl.activeTexture(gl.TEXTURE0 + pressureTexId);

gl.bindTexture(gl.TEXTURE_2D, pressure.first[0]);

gl.uniform1i(clearProgram.uniforms.uTexture, pressureTexId);

gl.uniform1f(clearProgram.uniforms.value, 0.8);

blit(pressure.second[1]);

pressure.swap();

pressureProgram.bind();

gl.uniform2f(pressureProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);

gl.uniform1i(pressureProgram.uniforms.uDivergence, divergence[2]);

pressureTexId = pressure.first[2];

gl.uniform1i(pressureProgram.uniforms.uPressure, pressureTexId);

gl.activeTexture(gl.TEXTURE0 + pressureTexId);

for (let i = 0; i < 25; i++) {

gl.bindTexture(gl.TEXTURE_2D, pressure.first[0]);

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);

yield ++i;

}

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