'use strict';

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

let config = {
TEXTURE_DOWNSAMPLE: 1,
DENSITY_DISSIPATION: 0.98,
VELOCITY_DISSIPATION: 0.99,
PRESSURE_DISSIPATION: 0.8,
PRESSURE_ITERATIONS: 25,
CURL: 28,
SPLAT_RADIUS: 0.004 };


let pointers = [];
let splatStack = [];

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

function getWebGLContext(canvas) {
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 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);
}

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 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];
}

pointers.push(new pointerPrototype());

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;
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);
}
`);

const 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);
}
`);

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

varying vec2 vUv;
uniform sampler2D uTexture;

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

const 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);
}
`);

const 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;
}
`);

const 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);
gl_FragColor.a = 1.0;
}
`);

const 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);
}
`);

const 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);
}
`);

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

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

void main () {
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), 0.0);
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);
}
`);

const 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);
}
`);

const 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);
}
`);

let textureWidth;
let textureHeight;
let density;
let velocity;
let divergence;
let curl;
let pressure;
initFramebuffers();

const clearProgram = new GLProgram(baseVertexShader, clearShader);
const displayProgram = new GLProgram(baseVertexShader, displayShader);
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() {
textureWidth = gl.drawingBufferWidth >> config.TEXTURE_DOWNSAMPLE;
textureHeight = gl.drawingBufferHeight >> config.TEXTURE_DOWNSAMPLE;

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

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

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;
} };

}

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 lastTime = Date.now();
multipleSplats(parseInt(Math.random() * 20) + 5);
update();

function update() {
resizeCanvas();

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

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.read[2]);
gl.uniform1i(advectionProgram.uniforms.uSource, velocity.read[2]);
gl.uniform1f(advectionProgram.uniforms.dt, dt);
gl.uniform1f(advectionProgram.uniforms.dissipation, config.VELOCITY_DISSIPATION);
blit(velocity.write[1]);
velocity.swap();

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

for (let i = 0; i < pointers.length; i++) {
const 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.read[2]);
blit(curl[1]);

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

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

clearProgram.bind();
let pressureTexId = pressure.read[2];
gl.activeTexture(gl.TEXTURE0 + pressureTexId);
gl.bindTexture(gl.TEXTURE_2D, pressure.read[0]);
gl.uniform1i(clearProgram.uniforms.uTexture, pressureTexId);
gl.uniform1f(clearProgram.uniforms.value, config.PRESSURE_DISSIPATION);
blit(pressure.write[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.read[2];
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[0]);
blit(pressure.write[1]);
pressure.swap();
}

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

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

requestAnimationFrame(update);
}

function splat(x, y, dx, dy, color) {
splatProgram.bind();
gl.uniform1i(splatProgram.uniforms.uTarget, velocity.read[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, config.SPLAT_RADIUS);
blit(velocity.write[1]);
velocity.swap();

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

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) * 10.0;
pointers[0].dy = (e.offsetY - pointers[0].y) * 10.0;
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) * 10.0;
pointer.dy = (touches[i].pageY - pointer.y) * 10.0;
pointer.x = touches[i].pageX;
pointer.y = touches[i].pageY;
}
}, false);

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

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 = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
}
});

window.addEventListener('mouseleave', () => {
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;
});