<template>
  <div class="fixed top-0 left-0 z-50 pointer-events-none w-full h-full">
    <canvas ref="canvasRef" id="fluid" class="w-screen h-screen block"></canvas>
  </div>
</template>

<script setup lang="ts">
import { onMounted, withDefaults, useTemplateRef } from 'vue';

/* ---------- types ---------- */
interface ColorRGB {
  r: number;
  g: number;
  b: number;
}

interface SplashCursorProps {
  SIM_RESOLUTION?: number;
  DYE_RESOLUTION?: number;
  CAPTURE_RESOLUTION?: number;
  DENSITY_DISSIPATION?: number;
  VELOCITY_DISSIPATION?: number;
  PRESSURE?: number;
  PRESSURE_ITERATIONS?: number;
  CURL?: number;
  SPLAT_RADIUS?: number;
  SPLAT_FORCE?: number;
  SHADING?: boolean;
  COLOR_UPDATE_SPEED?: number;
  BACK_COLOR?: ColorRGB;
  TRANSPARENT?: boolean;
}

/* ---------- props & defaults ---------- */
const props = withDefaults(defineProps<SplashCursorProps>(), {
  SIM_RESOLUTION: 128,
  DYE_RESOLUTION: 1440,
  CAPTURE_RESOLUTION: 512,
  DENSITY_DISSIPATION: 3.5,
  VELOCITY_DISSIPATION: 2,
  PRESSURE: 0.1,
  PRESSURE_ITERATIONS: 20,
  CURL: 3,
  SPLAT_RADIUS: 0.2,
  SPLAT_FORCE: 6000,
  SHADING: true,
  COLOR_UPDATE_SPEED: 10,
  BACK_COLOR: () => ({ r: 0.5, g: 0, b: 0 }),
  TRANSPARENT: true
});

/* ---------- refs ---------- */
const canvasRef = useTemplateRef<HTMLCanvasElement>('canvasRef');

/* ---------- helper types ---------- */
interface Pointer {
  id: number;
  texcoordX: number;
  texcoordY: number;
  prevTexcoordX: number;
  prevTexcoordY: number;
  deltaX: number;
  deltaY: number;
  down: boolean;
  moved: boolean;
  color: ColorRGB;
}

function pointerPrototype(): Pointer {
  return {
    id: -1,
    texcoordX: 0,
    texcoordY: 0,
    prevTexcoordX: 0,
    prevTexcoordY: 0,
    deltaX: 0,
    deltaY: 0,
    down: false,
    moved: false,
    color: { r: 0, g: 0, b: 0 }
  };
}

/* ---------- main logic ---------- */
onMounted(() => {
  const canvas = canvasRef.value;
  if (!canvas) return;

  const pointers: Pointer[] = [pointerPrototype()];

  const config = {
    SIM_RESOLUTION: props.SIM_RESOLUTION!,
    DYE_RESOLUTION: props.DYE_RESOLUTION!,
    CAPTURE_RESOLUTION: props.CAPTURE_RESOLUTION!,
    DENSITY_DISSIPATION: props.DENSITY_DISSIPATION!,
    VELOCITY_DISSIPATION: props.VELOCITY_DISSIPATION!,
    PRESSURE: props.PRESSURE!,
    PRESSURE_ITERATIONS: props.PRESSURE_ITERATIONS!,
    CURL: props.CURL!,
    SPLAT_RADIUS: props.SPLAT_RADIUS!,
    SPLAT_FORCE: props.SPLAT_FORCE!,
    SHADING: props.SHADING,
    COLOR_UPDATE_SPEED: props.COLOR_UPDATE_SPEED!,
    PAUSED: false,
    BACK_COLOR: props.BACK_COLOR,
    TRANSPARENT: props.TRANSPARENT
  };

  /* ---------- WebGL context helpers ---------- */
  const { gl, ext } = getWebGLContext(canvas);
  if (!gl || !ext) return;

  if (!ext.supportLinearFiltering) {
    config.DYE_RESOLUTION = 256;
    config.SHADING = false;
  }

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

    let gl = canvasEl.getContext('webgl2', params) as WebGL2RenderingContext | null;

    if (!gl) {
      gl = (canvasEl.getContext('webgl', params) ||
        canvasEl.getContext('experimental-webgl', params)) as WebGL2RenderingContext | null;
    }

    if (!gl) {
      throw new Error('Unable to initialize WebGL.');
    }

    const isWebGL2 = 'drawBuffers' in gl;

    let supportLinearFiltering = false;
    let halfFloat: OES_texture_half_float | null = null;

    if (isWebGL2) {
      (gl as WebGL2RenderingContext).getExtension('EXT_color_buffer_float');
      supportLinearFiltering = !!(gl as WebGL2RenderingContext).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, 1);

    const halfFloatTexType = isWebGL2
      ? (gl as WebGL2RenderingContext).HALF_FLOAT
      : (halfFloat && (halfFloat as OES_texture_half_float).HALF_FLOAT_OES) || 0;

    let formatRGBA: { internalFormat: number; format: number } | null;
    let formatRG: { internalFormat: number; format: number } | null;
    let formatR: { internalFormat: number; format: number } | null;

    if (isWebGL2) {
      formatRGBA = getSupportedFormat(gl, (gl as WebGL2RenderingContext).RGBA16F, gl.RGBA, halfFloatTexType);
      formatRG = getSupportedFormat(
        gl,
        (gl as WebGL2RenderingContext).RG16F,
        (gl as WebGL2RenderingContext).RG,
        halfFloatTexType
      );
      formatR = getSupportedFormat(
        gl,
        (gl as WebGL2RenderingContext).R16F,
        (gl as WebGL2RenderingContext).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: WebGLRenderingContext | WebGL2RenderingContext,
    internalFormat: number,
    format: number,
    type: number
  ): { internalFormat: number; format: number } | null {
    if (!supportRenderTextureFormat(gl, internalFormat, format, type)) {
      if ('drawBuffers' in gl) {
        const gl2 = gl as WebGL2RenderingContext;
        switch (internalFormat) {
          case gl2.R16F:
            return getSupportedFormat(gl2, gl2.RG16F, gl2.RG, type);
          case gl2.RG16F:
            return getSupportedFormat(gl2, gl2.RGBA16F, gl2.RGBA, type);
          default:
            return null;
        }
      }
      return null;
    }
    return { internalFormat, format };
  }

  function supportRenderTextureFormat(
    gl: WebGLRenderingContext | WebGL2RenderingContext,
    internalFormat: number,
    format: number,
    type: number
  ) {
    const texture = gl.createTexture();
    if (!texture) return false;

    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);

    const fbo = gl.createFramebuffer();
    if (!fbo) return false;

    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 hashCode(s: string) {
    if (!s.length) return 0;
    let hash = 0;
    for (let i = 0; i < s.length; i++) {
      hash = (hash << 5) - hash + s.charCodeAt(i);
      hash |= 0;
    }
    return hash;
  }

  function addKeywords(source: string, keywords: string[] | null) {
    if (!keywords) return source;
    let keywordsString = '';
    for (const keyword of keywords) {
      keywordsString += `#define ${keyword}\n`;
    }
    return keywordsString + source;
  }

  function compileShader(type: number, source: string, keywords: string[] | null = null): WebGLShader | null {
    const shaderSource = addKeywords(source, keywords);
    const shader = gl.createShader(type);
    if (!shader) return null;
    gl.shaderSource(shader, shaderSource);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      console.trace(gl.getShaderInfoLog(shader));
    }
    return shader;
  }

  function createProgram(vertexShader: WebGLShader | null, fragmentShader: WebGLShader | null): WebGLProgram | null {
    if (!vertexShader || !fragmentShader) return null;
    const program = gl.createProgram();
    if (!program) return null;
    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);
    gl.linkProgram(program);
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
      console.trace(gl.getProgramInfoLog(program));
    }
    return program;
  }

  function getUniforms(program: WebGLProgram) {
    const uniforms: Record<string, WebGLUniformLocation | null> = {};
    const uniformCount = gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS);
    for (let i = 0; i < uniformCount; i++) {
      const uniformInfo = gl.getActiveUniform(program, i);
      if (uniformInfo) {
        uniforms[uniformInfo.name] = gl.getUniformLocation(program, uniformInfo.name);
      }
    }
    return uniforms;
  }

  class Program {
    program: WebGLProgram | null;
    uniforms: Record<string, WebGLUniformLocation | null>;

    constructor(vertexShader: WebGLShader | null, fragmentShader: WebGLShader | null) {
      this.program = createProgram(vertexShader, fragmentShader);
      this.uniforms = this.program ? getUniforms(this.program) : {};
    }

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

  class Material {
    vertexShader: WebGLShader | null;
    fragmentShaderSource: string;
    programs: Record<number, WebGLProgram | null>;
    activeProgram: WebGLProgram | null;
    uniforms: Record<string, WebGLUniformLocation | null>;

    constructor(vertexShader: WebGLShader | null, fragmentShaderSource: string) {
      this.vertexShader = vertexShader;
      this.fragmentShaderSource = fragmentShaderSource;
      this.programs = {};
      this.activeProgram = null;
      this.uniforms = {};
    }

    setKeywords(keywords: string[]) {
      let hash = 0;
      for (const kw of keywords) {
        hash += hashCode(kw);
      }
      let program = this.programs[hash];
      if (program == null) {
        const fragmentShader = compileShader(gl.FRAGMENT_SHADER, this.fragmentShaderSource, keywords);
        program = createProgram(this.vertexShader, fragmentShader);
        this.programs[hash] = program;
      }
      if (program === this.activeProgram) return;
      if (program) {
        this.uniforms = getUniforms(program);
      }
      this.activeProgram = program;
    }

    bind() {
      if (this.activeProgram) {
        gl.useProgram(this.activeProgram);
      }
    }
  }

  /* ---------- shaders ---------- */
  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 copyShader = compileShader(
    gl.FRAGMENT_SHADER,
    `
      precision mediump float;
      precision mediump sampler2D;
      varying highp vec2 vUv;
      uniform sampler2D uTexture;
      void main () {
        gl_FragColor = texture2D(uTexture, vUv);
      }
    `
  );

  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 displayShaderSource = `
      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 sampler2D uDithering;
      uniform vec2 ditherScale;
      uniform vec2 texelSize;
      vec3 linearToGamma (vec3 color) {
          color = max(color, vec3(0));
          return max(1.055 * pow(color, vec3(0.416666667)) - 0.055, vec3(0));
      }
      void main () {
          vec3 c = texture2D(uTexture, vUv).rgb;
          #ifdef SHADING
              vec3 lc = texture2D(uTexture, vL).rgb;
              vec3 rc = texture2D(uTexture, vR).rgb;
              vec3 tc = texture2D(uTexture, vT).rgb;
              vec3 bc = texture2D(uTexture, vB).rgb;
              float dx = length(rc) - length(lc);
              float dy = length(tc) - length(bc);
              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 *= diffuse;
          #endif
          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 advectionShader = 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 () {
          #ifdef MANUAL_FILTERING
              vec2 coord = vUv - dt * bilerp(uVelocity, vUv, texelSize).xy * texelSize;
              vec4 result = bilerp(uSource, coord, dyeTexelSize);
          #else
              vec2 coord = vUv - dt * texture2D(uVelocity, vUv).xy * texelSize;
              vec4 result = texture2D(uSource, coord);
          #endif
          float decay = 1.0 + dissipation * dt;
          gl_FragColor = result / decay;
      }
    `,
    ext.supportLinearFiltering ? null : ['MANUAL_FILTERING']
  );

  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 velocity = texture2D(uVelocity, vUv).xy;
          velocity += force * dt;
          velocity = min(max(velocity, -1000.0), 1000.0);
          gl_FragColor = vec4(velocity, 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;
      void main () {
          float L = texture2D(uPressure, vL).x;
          float R = texture2D(uPressure, vR).x;
          float T = texture2D(uPressure, vT).x;
          float B = texture2D(uPressure, 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;
      void main () {
          float L = texture2D(uPressure, vL).x;
          float R = texture2D(uPressure, vR).x;
          float T = texture2D(uPressure, vT).x;
          float B = texture2D(uPressure, vB).x;
          vec2 velocity = texture2D(uVelocity, vUv).xy;
          velocity.xy -= vec2(R - L, T - B);
          gl_FragColor = vec4(velocity, 0.0, 1.0);
      }
    `
  );

  /* ---------- geometry helper ---------- */
  const blit = (() => {
    const buffer = gl.createBuffer()!;
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, -1, 1, 1, 1, 1, -1]), gl.STATIC_DRAW);
    const elemBuffer = gl.createBuffer()!;
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, elemBuffer);
    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 (target: FBO | null, doClear = false) => {
      if (!gl) return;
      if (!target) {
        gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
        gl.bindFramebuffer(gl.FRAMEBUFFER, null);
      } else {
        gl.viewport(0, 0, target.width, target.height);
        gl.bindFramebuffer(gl.FRAMEBUFFER, target.fbo);
      }
      if (doClear) {
        gl.clearColor(0, 0, 0, 1);
        gl.clear(gl.COLOR_BUFFER_BIT);
      }
      gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_SHORT, 0);
    };
  })();

  /* ---------- frame-buffer object helpers ---------- */
  interface FBO {
    texture: WebGLTexture;
    fbo: WebGLFramebuffer;
    width: number;
    height: number;
    texelSizeX: number;
    texelSizeY: number;
    attach: (id: number) => number;
  }

  interface DoubleFBO {
    width: number;
    height: number;
    texelSizeX: number;
    texelSizeY: number;
    read: FBO;
    write: FBO;
    swap: () => void;
  }

  let dye: DoubleFBO;
  let velocity: DoubleFBO;
  let divergence: FBO;
  let curl: FBO;
  let pressure: DoubleFBO;

  const copyProgram = new Program(baseVertexShader, copyShader);
  const clearProgram = new Program(baseVertexShader, clearShader);
  const splatProgram = new Program(baseVertexShader, splatShader);
  const advectionProgram = new Program(baseVertexShader, advectionShader);
  const divergenceProgram = new Program(baseVertexShader, divergenceShader);
  const curlProgram = new Program(baseVertexShader, curlShader);
  const vorticityProgram = new Program(baseVertexShader, vorticityShader);
  const pressureProgram = new Program(baseVertexShader, pressureShader);
  const gradienSubtractProgram = new Program(baseVertexShader, gradientSubtractShader);
  const displayMaterial = new Material(baseVertexShader, displayShaderSource);

  function createFBO(w: number, h: number, internalFormat: number, format: number, type: number, param: number): FBO {
    gl.activeTexture(gl.TEXTURE0);
    const 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);
    const 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);
    const texelSizeX = 1 / w;
    const texelSizeY = 1 / h;
    return {
      texture,
      fbo,
      width: w,
      height: h,
      texelSizeX,
      texelSizeY,
      attach(id: number) {
        gl.activeTexture(gl.TEXTURE0 + id);
        gl.bindTexture(gl.TEXTURE_2D, texture);
        return id;
      }
    };
  }

  function createDoubleFBO(
    w: number,
    h: number,
    internalFormat: number,
    format: number,
    type: number,
    param: number
  ): DoubleFBO {
    const fbo1 = createFBO(w, h, internalFormat, format, type, param);
    const fbo2 = createFBO(w, h, internalFormat, format, type, param);
    return {
      width: w,
      height: h,
      texelSizeX: fbo1.texelSizeX,
      texelSizeY: fbo1.texelSizeY,
      read: fbo1,
      write: fbo2,
      swap() {
        const tmp = this.read;
        this.read = this.write;
        this.write = tmp;
      }
    };
  }

  function resizeFBO(
    target: FBO,
    w: number,
    h: number,
    internalFormat: number,
    format: number,
    type: number,
    param: number
  ) {
    const newFBO = createFBO(w, h, internalFormat, format, type, param);
    copyProgram.bind();
    if (copyProgram.uniforms.uTexture) gl.uniform1i(copyProgram.uniforms.uTexture, target.attach(0));
    blit(newFBO, false);
    return newFBO;
  }

  function resizeDoubleFBO(
    target: DoubleFBO,
    w: number,
    h: number,
    internalFormat: number,
    format: number,
    type: number,
    param: number
  ) {
    if (target.width === w && target.height === h) return target;
    target.read = resizeFBO(target.read, w, h, internalFormat, format, type, param);
    target.write = createFBO(w, h, internalFormat, format, type, param);
    target.width = w;
    target.height = h;
    target.texelSizeX = 1 / w;
    target.texelSizeY = 1 / h;
    return target;
  }

  function initFramebuffers() {
    const simRes = getResolution(config.SIM_RESOLUTION!);
    const dyeRes = getResolution(config.DYE_RESOLUTION!);
    const texType = ext.halfFloatTexType;
    const rgba = ext.formatRGBA;
    const rg = ext.formatRG;
    const r = ext.formatR;
    const filtering = ext.supportLinearFiltering ? gl.LINEAR : gl.NEAREST;
    gl.disable(gl.BLEND);

    if (!rgba) return;

    if (!dye) {
      dye = createDoubleFBO(dyeRes.width, dyeRes.height, rgba.internalFormat, rgba.format, texType, filtering);
    } else {
      dye = resizeDoubleFBO(dye, dyeRes.width, dyeRes.height, rgba.internalFormat, rgba.format, texType, filtering);
    }

    if (!rg) return;

    if (!velocity) {
      velocity = createDoubleFBO(simRes.width, simRes.height, rg.internalFormat, rg.format, texType, filtering);
    } else {
      velocity = resizeDoubleFBO(
        velocity,
        simRes.width,
        simRes.height,
        rg.internalFormat,
        rg.format,
        texType,
        filtering
      );
    }

    if (!r) return;

    divergence = createFBO(simRes.width, simRes.height, r.internalFormat, r.format, texType, gl.NEAREST);
    curl = createFBO(simRes.width, simRes.height, r.internalFormat, r.format, texType, gl.NEAREST);
    pressure = createDoubleFBO(simRes.width, simRes.height, r.internalFormat, r.format, texType, gl.NEAREST);
  }

  function updateKeywords() {
    const displayKeywords: string[] = [];
    if (config.SHADING) displayKeywords.push('SHADING');
    displayMaterial.setKeywords(displayKeywords);
  }

  function getResolution(resolution: number) {
    const w = gl.drawingBufferWidth;
    const h = gl.drawingBufferHeight;
    const aspectRatio = w / h;
    const aspect = aspectRatio < 1 ? 1 / aspectRatio : aspectRatio;
    const min = Math.round(resolution);
    const max = Math.round(resolution * aspect);
    if (w > h) {
      return { width: max, height: min };
    }
    return { width: min, height: max };
  }

  function scaleByPixelRatio(input: number) {
    const pixelRatio = window.devicePixelRatio || 1;
    return Math.floor(input * pixelRatio);
  }

  updateKeywords();
  initFramebuffers();

  let lastUpdateTime = Date.now();
  let colorUpdateTimer = 0.0;

  function updateFrame() {
    const dt = calcDeltaTime();
    if (resizeCanvas()) initFramebuffers();
    updateColors(dt);
    applyInputs();
    step(dt);
    render(null);
    requestAnimationFrame(updateFrame);
  }

  function calcDeltaTime() {
    const now = Date.now();
    let dt = (now - lastUpdateTime) / 1000;
    dt = Math.min(dt, 0.016666);
    lastUpdateTime = now;
    return dt;
  }

  function resizeCanvas() {
    const width = scaleByPixelRatio(canvas!.clientWidth);
    const height = scaleByPixelRatio(canvas!.clientHeight);
    if (canvas!.width !== width || canvas!.height !== height) {
      canvas!.width = width;
      canvas!.height = height;
      return true;
    }
    return false;
  }

  function updateColors(dt: number) {
    colorUpdateTimer += dt * config.COLOR_UPDATE_SPEED;
    if (colorUpdateTimer >= 1) {
      colorUpdateTimer = wrap(colorUpdateTimer, 0, 1);
      pointers.forEach(p => {
        p.color = generateColor();
      });
    }
  }

  function applyInputs() {
    for (const p of pointers) {
      if (p.moved) {
        p.moved = false;
        splatPointer(p);
      }
    }
  }

  /* ---------- simulation step ---------- */
  function step(dt: number) {
    gl.disable(gl.BLEND);

    curlProgram.bind();
    if (curlProgram.uniforms.texelSize) {
      gl.uniform2f(curlProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (curlProgram.uniforms.uVelocity) {
      gl.uniform1i(curlProgram.uniforms.uVelocity, velocity.read.attach(0));
    }
    blit(curl);

    vorticityProgram.bind();
    if (vorticityProgram.uniforms.texelSize) {
      gl.uniform2f(vorticityProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (vorticityProgram.uniforms.uVelocity) {
      gl.uniform1i(vorticityProgram.uniforms.uVelocity, velocity.read.attach(0));
    }
    if (vorticityProgram.uniforms.uCurl) {
      gl.uniform1i(vorticityProgram.uniforms.uCurl, curl.attach(1));
    }
    if (vorticityProgram.uniforms.curl) {
      gl.uniform1f(vorticityProgram.uniforms.curl, config.CURL);
    }
    if (vorticityProgram.uniforms.dt) {
      gl.uniform1f(vorticityProgram.uniforms.dt, dt);
    }
    blit(velocity.write);
    velocity.swap();

    divergenceProgram.bind();
    if (divergenceProgram.uniforms.texelSize) {
      gl.uniform2f(divergenceProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (divergenceProgram.uniforms.uVelocity) {
      gl.uniform1i(divergenceProgram.uniforms.uVelocity, velocity.read.attach(0));
    }
    blit(divergence);

    clearProgram.bind();
    if (clearProgram.uniforms.uTexture) {
      gl.uniform1i(clearProgram.uniforms.uTexture, pressure.read.attach(0));
    }
    if (clearProgram.uniforms.value) {
      gl.uniform1f(clearProgram.uniforms.value, config.PRESSURE);
    }
    blit(pressure.write);
    pressure.swap();

    pressureProgram.bind();
    if (pressureProgram.uniforms.texelSize) {
      gl.uniform2f(pressureProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (pressureProgram.uniforms.uDivergence) {
      gl.uniform1i(pressureProgram.uniforms.uDivergence, divergence.attach(0));
    }
    for (let i = 0; i < config.PRESSURE_ITERATIONS; i++) {
      if (pressureProgram.uniforms.uPressure) {
        gl.uniform1i(pressureProgram.uniforms.uPressure, pressure.read.attach(1));
      }
      blit(pressure.write);
      pressure.swap();
    }

    gradienSubtractProgram.bind();
    if (gradienSubtractProgram.uniforms.texelSize) {
      gl.uniform2f(gradienSubtractProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (gradienSubtractProgram.uniforms.uPressure) {
      gl.uniform1i(gradienSubtractProgram.uniforms.uPressure, pressure.read.attach(0));
    }
    if (gradienSubtractProgram.uniforms.uVelocity) {
      gl.uniform1i(gradienSubtractProgram.uniforms.uVelocity, velocity.read.attach(1));
    }
    blit(velocity.write);
    velocity.swap();

    advectionProgram.bind();
    if (advectionProgram.uniforms.texelSize) {
      gl.uniform2f(advectionProgram.uniforms.texelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    if (!ext.supportLinearFiltering && advectionProgram.uniforms.dyeTexelSize) {
      gl.uniform2f(advectionProgram.uniforms.dyeTexelSize, velocity.texelSizeX, velocity.texelSizeY);
    }
    const velocityId = velocity.read.attach(0);
    if (advectionProgram.uniforms.uVelocity) {
      gl.uniform1i(advectionProgram.uniforms.uVelocity, velocityId);
    }
    if (advectionProgram.uniforms.uSource) {
      gl.uniform1i(advectionProgram.uniforms.uSource, velocityId);
    }
    if (advectionProgram.uniforms.dt) {
      gl.uniform1f(advectionProgram.uniforms.dt, dt);
    }
    if (advectionProgram.uniforms.dissipation) {
      gl.uniform1f(advectionProgram.uniforms.dissipation, config.VELOCITY_DISSIPATION);
    }
    blit(velocity.write);
    velocity.swap();

    if (!ext.supportLinearFiltering && advectionProgram.uniforms.dyeTexelSize) {
      gl.uniform2f(advectionProgram.uniforms.dyeTexelSize, dye.texelSizeX, dye.texelSizeY);
    }
    if (advectionProgram.uniforms.uVelocity) {
      gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.read.attach(0));
    }
    if (advectionProgram.uniforms.uSource) {
      gl.uniform1i(advectionProgram.uniforms.uSource, dye.read.attach(1));
    }
    if (advectionProgram.uniforms.dissipation) {
      gl.uniform1f(advectionProgram.uniforms.dissipation, config.DENSITY_DISSIPATION);
    }
    blit(dye.write);
    dye.swap();
  }

  /* ---------- render ---------- */
  function render(target: FBO | null) {
    gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
    gl.enable(gl.BLEND);
    drawDisplay(target);
  }

  function drawDisplay(target: FBO | null) {
    const width = target ? target.width : gl.drawingBufferWidth;
    const height = target ? target.height : gl.drawingBufferHeight;
    displayMaterial.bind();
    if (config.SHADING && displayMaterial.uniforms.texelSize) {
      gl.uniform2f(displayMaterial.uniforms.texelSize, 1 / width, 1 / height);
    }
    if (displayMaterial.uniforms.uTexture) {
      gl.uniform1i(displayMaterial.uniforms.uTexture, dye.read.attach(0));
    }
    blit(target, false);
  }

  /* ---------- splats ---------- */
  function splatPointer(pointer: Pointer) {
    const dx = pointer.deltaX * config.SPLAT_FORCE;
    const dy = pointer.deltaY * config.SPLAT_FORCE;
    splat(pointer.texcoordX, pointer.texcoordY, dx, dy, pointer.color);
  }

  function clickSplat(pointer: Pointer) {
    const color = generateColor();
    color.r *= 10;
    color.g *= 10;
    color.b *= 10;
    const dx = 10 * (Math.random() - 0.5);
    const dy = 30 * (Math.random() - 0.5);
    splat(pointer.texcoordX, pointer.texcoordY, dx, dy, color);
  }

  function splat(x: number, y: number, dx: number, dy: number, color: ColorRGB) {
    splatProgram.bind();
    if (splatProgram.uniforms.uTarget) {
      gl.uniform1i(splatProgram.uniforms.uTarget, velocity.read.attach(0));
    }
    if (splatProgram.uniforms.aspectRatio) {
      gl.uniform1f(splatProgram.uniforms.aspectRatio, canvas!.width / canvas!.height);
    }
    if (splatProgram.uniforms.point) {
      gl.uniform2f(splatProgram.uniforms.point, x, y);
    }
    if (splatProgram.uniforms.color) {
      gl.uniform3f(splatProgram.uniforms.color, dx, dy, 0);
    }
    if (splatProgram.uniforms.radius) {
      gl.uniform1f(splatProgram.uniforms.radius, correctRadius(config.SPLAT_RADIUS / 100)!);
    }
    blit(velocity.write);
    velocity.swap();

    if (splatProgram.uniforms.uTarget) {
      gl.uniform1i(splatProgram.uniforms.uTarget, dye.read.attach(0));
    }
    if (splatProgram.uniforms.color) {
      gl.uniform3f(splatProgram.uniforms.color, color.r, color.g, color.b);
    }
    blit(dye.write);
    dye.swap();
  }

  function correctRadius(radius: number) {
    const aspectRatio = canvas!.width / canvas!.height;
    if (aspectRatio > 1) radius *= aspectRatio;
    return radius;
  }

  /* ---------- pointer helpers ---------- */
  function updatePointerDownData(pointer: Pointer, id: number, posX: number, posY: number) {
    pointer.id = id;
    pointer.down = true;
    pointer.moved = false;
    pointer.texcoordX = posX / canvas!.width;
    pointer.texcoordY = 1 - posY / canvas!.height;
    pointer.prevTexcoordX = pointer.texcoordX;
    pointer.prevTexcoordY = pointer.texcoordY;
    pointer.deltaX = 0;
    pointer.deltaY = 0;
    pointer.color = generateColor();
  }

  function updatePointerMoveData(pointer: Pointer, posX: number, posY: number, color: ColorRGB) {
    pointer.prevTexcoordX = pointer.texcoordX;
    pointer.prevTexcoordY = pointer.texcoordY;
    pointer.texcoordX = posX / canvas!.width;
    pointer.texcoordY = 1 - posY / canvas!.height;
    pointer.deltaX = correctDeltaX(pointer.texcoordX - pointer.prevTexcoordX)!;
    pointer.deltaY = correctDeltaY(pointer.texcoordY - pointer.prevTexcoordY)!;
    pointer.moved = Math.abs(pointer.deltaX) > 0 || Math.abs(pointer.deltaY) > 0;
    pointer.color = color;
  }

  function updatePointerUpData(pointer: Pointer) {
    pointer.down = false;
  }

  function correctDeltaX(delta: number) {
    const aspectRatio = canvas!.width / canvas!.height;
    if (aspectRatio < 1) delta *= aspectRatio;
    return delta;
  }

  function correctDeltaY(delta: number) {
    const aspectRatio = canvas!.width / canvas!.height;
    if (aspectRatio > 1) delta /= aspectRatio;
    return delta;
  }

  /* ---------- color helpers ---------- */
  function generateColor(): ColorRGB {
    const 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: number, s: number, v: number): ColorRGB {
    let r = 0,
      g = 0,
      b = 0;
    const i = Math.floor(h * 6);
    const f = h * 6 - i;
    const p = v * (1 - s);
    const q = v * (1 - f * s);
    const 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 };
  }

  function wrap(value: number, min: number, max: number) {
    const range = max - min;
    if (range === 0) return min;
    return ((value - min) % range) + min;
  }

  /* ---------- input events ---------- */
  window.addEventListener('mousedown', e => {
    const pointer = pointers[0];
    const posX = scaleByPixelRatio(e.clientX);
    const posY = scaleByPixelRatio(e.clientY);
    updatePointerDownData(pointer, -1, posX, posY);
    clickSplat(pointer);
  });

  function handleFirstMouseMove(e: MouseEvent) {
    const pointer = pointers[0];
    const posX = scaleByPixelRatio(e.clientX);
    const posY = scaleByPixelRatio(e.clientY);
    const color = generateColor();
    updateFrame();
    updatePointerMoveData(pointer, posX, posY, color);
    document.body.removeEventListener('mousemove', handleFirstMouseMove);
  }
  document.body.addEventListener('mousemove', handleFirstMouseMove);

  window.addEventListener('mousemove', e => {
    const pointer = pointers[0];
    const posX = scaleByPixelRatio(e.clientX);
    const posY = scaleByPixelRatio(e.clientY);
    const color = pointer.color;
    updatePointerMoveData(pointer, posX, posY, color);
  });

  function handleFirstTouchStart(e: TouchEvent) {
    const touches = e.targetTouches;
    const pointer = pointers[0];
    for (let i = 0; i < touches.length; i++) {
      const posX = scaleByPixelRatio(touches[i].clientX);
      const posY = scaleByPixelRatio(touches[i].clientY);
      updateFrame();
      updatePointerDownData(pointer, touches[i].identifier, posX, posY);
    }
    document.body.removeEventListener('touchstart', handleFirstTouchStart);
  }
  document.body.addEventListener('touchstart', handleFirstTouchStart);

  window.addEventListener(
    'touchstart',
    e => {
      const touches = e.targetTouches;
      const pointer = pointers[0];
      for (let i = 0; i < touches.length; i++) {
        const posX = scaleByPixelRatio(touches[i].clientX);
        const posY = scaleByPixelRatio(touches[i].clientY);
        updatePointerDownData(pointer, touches[i].identifier, posX, posY);
      }
    },
    false
  );

  window.addEventListener(
    'touchmove',
    e => {
      const touches = e.targetTouches;
      const pointer = pointers[0];
      for (let i = 0; i < touches.length; i++) {
        const posX = scaleByPixelRatio(touches[i].clientX);
        const posY = scaleByPixelRatio(touches[i].clientY);
        updatePointerMoveData(pointer, posX, posY, pointer.color);
      }
    },
    false
  );

  window.addEventListener('touchend', e => {
    const touches = e.changedTouches;
    const pointer = pointers[0];
    for (let i = 0; i < touches.length; i++) {
      updatePointerUpData(pointer);
    }
  });
});
</script>
