examples/transform-feedback.html

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    <title>twgl.js - transform feedback</title>
    <style>
      body {
          margin: 0;
          font-family: monospace;
      }
      canvas {
          display: block;
          width: 100vw;
          height: 100vh;
      }
      #b {
        position: absolute;
        top: 10px;
        width: 100%;
        text-align: center;
        z-index: 2;
      }
    </style>
  </head>
  <body>
    <canvas id="c"></canvas>
    <div id="b"><a href="http://twgljs.org">twgl.js</a> - transform feedback</div>
    <div id="no-webgl2" style="display: none;">
      <div>Sorry but your browser doesn't appear to support WebGL2</div>
    </div>
  </body>
  <script id="tf-vs" type="nonjs">
#version 300 es

out vec3 a_position;
out vec3 a_normal;
out vec2 a_texcoord;
flat out uint a_color;

uniform float u_vertexCount;
uniform float u_around;
uniform float u_hue;

const float PI = radians(180.);

vec3 hsv2rgb(vec3 c) {
  c = vec3(c.x, clamp(c.yz, 0.0, 1.0));
  vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
  vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
  return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

void main() {
  float numQuads = floor(u_vertexCount / 6.);
  float down = numQuads / u_around;
  float quadId = floor(float(gl_VertexID) / 6.);

  float qx = mod(quadId, u_around);
  float qy = floor(quadId / u_around);

  // 0--1 3
  // | / /|
  // |/ / |
  // 2 4--5
  //
  // 0 1 0 1 0 1
  // 0 0 1 0 1 1

  float edgeId = mod(float(gl_VertexID), 6.);
  float ux = mod(edgeId, 2.);
  float vy = mod(floor(edgeId / 2.) + floor(edgeId / 3.), 2.);

  float qu = (qx + ux) / u_around;
  float qv = (qy + vy) / down;

  float r = sin(qv * PI);
  float x = cos(qu * PI * 2.) * r;
  float z = sin(qu * PI * 2.) * r;

  a_position = vec3(x, cos(qv * PI), z);
  a_normal = normalize(a_position);
  a_texcoord = vec2(qu, qv);

  float hue = sin(qu * PI) * .1 + u_hue;
  float sat = mix(0.5, 1., mod(quadId, 2.));
  float val = 1.;
  uvec4 ucolor = uvec4(vec4(hsv2rgb(vec3(hue, sat, val)), 1.) * 255.);
  a_color = (ucolor.r <<  0) |
            (ucolor.g <<  8) |
            (ucolor.b << 16) |
            (ucolor.a << 24) ;
}
  </script>
  <script id="tf-fs" type="notjs">
#version 300 es
precision mediump float;
out vec4 o;
void main() {
  o = vec4(0);
}
  </script>
  <script id="vs" type="notjs">
uniform mat4 u_worldViewProjection;
uniform vec3 u_lightWorldPos;
uniform mat4 u_world;
uniform mat4 u_viewInverse;
uniform mat4 u_worldInverseTranspose;

attribute vec4 a_position;
attribute vec3 a_normal;
attribute vec2 a_texcoord;
attribute vec4 a_color;

varying vec4 v_position;
varying vec2 v_texCoord;
varying vec3 v_normal;
varying vec3 v_surfaceToLight;
varying vec3 v_surfaceToView;
varying vec4 v_color;

void main() {
  v_texCoord = a_texcoord;
  v_position = (u_worldViewProjection * a_position);
  v_color = a_color;
  v_normal = (u_worldInverseTranspose * vec4(a_normal, 0)).xyz;
  v_surfaceToLight = u_lightWorldPos - (u_world * a_position).xyz;
  v_surfaceToView = (u_viewInverse[3] - (u_world * a_position)).xyz;
  gl_Position = v_position;
}
  </script>
  <script id="fs" type="notjs">
precision mediump float;

varying vec4 v_position;
varying vec2 v_texCoord;
varying vec3 v_normal;
varying vec3 v_surfaceToLight;
varying vec3 v_surfaceToView;
varying vec4 v_color;

uniform vec4 u_lightColor;
uniform vec4 u_diffuseMult;
uniform sampler2D u_diffuse;
uniform vec4 u_specular;
uniform float u_shininess;
uniform float u_specularFactor;

vec4 lit(float l ,float h, float m) {
  return vec4(1.0,
              abs(l),//max(l, 0.0),
              (l > 0.0) ? pow(max(0.0, h), m) : 0.0,
              1.0);
}

void main() {
  vec4 diffuseColor = texture2D(u_diffuse, v_texCoord) * u_diffuseMult * v_color;
  vec3 a_normal = normalize(v_normal);
  vec3 surfaceToLight = normalize(v_surfaceToLight);
  vec3 surfaceToView = normalize(v_surfaceToView);
  vec3 halfVector = normalize(surfaceToLight + surfaceToView);
  vec4 litR = lit(dot(a_normal, surfaceToLight),
                    dot(a_normal, halfVector), u_shininess);
  vec4 outColor = vec4((
  u_lightColor * (diffuseColor * litR.y +
                u_specular * litR.z * u_specularFactor)).rgb,
      diffuseColor.a);
  gl_FragColor = outColor;
}
  </script>
  <script src="../3rdparty/chroma.min.js"></script>
  <script type="module">
import * as twgl from '../dist/6.x/twgl-full.module.js';
function main() {
  twgl.setDefaults({attribPrefix: "a_"});
  const m4 = twgl.m4;
  const gl = document.getElementById("c").getContext("webgl2");
  if (!gl) {
    document.querySelector("#no-webgl2").style.display = "";
    return;
  }

  // shaders to render with
  const programInfo = twgl.createProgramInfo(gl, ["vs", "fs"]);

  // shaders to generate a mesh
  const feedbackProgramInfo = twgl.createProgramInfo(gl, ["tf-vs", "tf-fs"], {
    // note: you can pass a bufferInfo instead of this array
    transformFeedbackVaryings: [
      "a_position",
      "a_normal",
      "a_texcoord",
      "a_color",
    ],
  });

  function generateMesh(tf, bufferInfo, numVerts, around, hue) {
    // Generate a mesh using transform feedback

    gl.enable(gl.RASTERIZER_DISCARD);

    gl.useProgram(feedbackProgramInfo.program);
    gl.bindTransformFeedback(gl.TRANSFORM_FEEDBACK, tf);
    gl.beginTransformFeedback(gl.TRIANGLES);
    twgl.setUniforms(feedbackProgramInfo, {
      u_vertexCount: numVerts,
      u_around: around,
      u_hue: hue,
    });
    twgl.drawBufferInfo(gl, bufferInfo);
    gl.endTransformFeedback();
    gl.bindTransformFeedback(gl.TRANSFORM_FEEDBACK, null);

    gl.disable(gl.RASTERIZER_DISCARD);
  }

  const shapes = [ ];

  // Make shapes using transform feedback
  [
    { around:  4, down:  3, hue: .2, },
    { around:  6, down:  4, hue: .4, },
    { around: 12, down:  6, hue: .6, },
    { around: 20, down: 10, hue: .8, },
    { around: 40, down: 20, hue: .0, },
  ].forEach(e => {
    const around = e.around;
    const down = e.down;
    const numQuads = around * down;
    const numVerts = numQuads * 6;

    const bufferInfo = twgl.createBufferInfoFromArrays(gl, {
      position: numVerts * 3,
      normal: numVerts * 3,
      texcoord: numVerts * 2,
      color: { data: numVerts * 4, type: Uint8Array, },
    });
    const tf = twgl.createTransformFeedback(gl, feedbackProgramInfo, bufferInfo);
    generateMesh(tf, bufferInfo, numVerts, down, e.hue);
    shapes.push(bufferInfo);
  });

  function rand(min, max) {
    return min + Math.random() * (max - min);
  }

  // Shared values
  const lightWorldPosition = [1, 8, -10];
  const lightColor = [1, 1, 1, 1];
  const camera = m4.identity();
  const view = m4.identity();
  const viewProjection = m4.identity();

  const tex = twgl.createTexture(gl, {
    min: gl.NEAREST,
    mag: gl.NEAREST,
    format: gl.LUMINANCE,
    src: [
      255, 128, 255, 128, 255, 128, 255, 128,
      128, 255, 128, 255, 128, 255, 128, 255,
      255, 128, 255, 128, 255, 128, 255, 128,
      128, 255, 128, 255, 128, 255, 128, 255,
      255, 128, 255, 128, 255, 128, 255, 128,
      128, 255, 128, 255, 128, 255, 128, 255,
      255, 128, 255, 128, 255, 128, 255, 128,
      128, 255, 128, 255, 128, 255, 128, 255,
    ],
  });

  const objects = [];
  const drawObjects = [];
  const numObjects = 100;
  for (let ii = 0; ii < numObjects; ++ii) {
    const uniforms = {
      u_lightWorldPos: lightWorldPosition,
      u_lightColor: lightColor,
      u_diffuseMult: [1, 1, 1, 1],
      u_specular: [1, 1, 1, 1],
      u_shininess: 50,
      u_specularFactor: 1,
      u_diffuse: tex,
      u_viewInverse: camera,
      u_world: m4.identity(),
      u_worldInverseTranspose: m4.identity(),
      u_worldViewProjection: m4.identity(),
    };
    drawObjects.push({
      programInfo: programInfo,
      bufferInfo: shapes[ii % shapes.length],
      uniforms: uniforms,
    });
    objects.push({
      translation: [rand(-10, 10), rand(-10, 10), rand(-10, 10)],
      ySpeed: rand(0.1, 0.3),
      zSpeed: rand(0.1, 0.3),
      uniforms: uniforms,
    });
  }

  function render(time) {
    time *= 0.001;
    twgl.resizeCanvasToDisplaySize(gl.canvas);
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    gl.enable(gl.DEPTH_TEST);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    const projection = m4.perspective(30 * Math.PI / 180, gl.canvas.clientWidth / gl.canvas.clientHeight, 0.5, 100);
    const eye = [1, 4, -20];
    const target = [0, 0, 0];
    const up = [0, 1, 0];

    m4.lookAt(eye, target, up, camera);
    m4.inverse(camera, view);
    m4.multiply(projection, view, viewProjection);

    objects.forEach(function(obj) {
      const uni = obj.uniforms;
      const world = uni.u_world;
      m4.identity(world);
      m4.rotateY(world, time * obj.ySpeed, world);
      m4.rotateZ(world, time * obj.zSpeed, world);
      m4.translate(world, obj.translation, world);
      m4.rotateX(world, time, world);
      m4.transpose(m4.inverse(world, uni.u_worldInverseTranspose), uni.u_worldInverseTranspose);
      m4.multiply(viewProjection, uni.u_world, uni.u_worldViewProjection);
    });

    twgl.drawObjectList(gl, drawObjects);

    requestAnimationFrame(render);
  }
  requestAnimationFrame(render);
}
main();
  </script>
</html>