webGL

<style>
body {
  margin: 0;
}
canvas {
  width: 100vw;
  height: 100vh;
  display: block;
}
</style>

<canvas id="c"></canvas>
  <script  id="vertex-shader-2d" type="notjs">

  // an attribute will receive data from a buffer
  attribute vec4 a_position;

  // all shaders have a main function
  void main() {

    // gl_Position is a special variable a vertex shader
    // is responsible for setting
    gl_Position = a_position;
  }

</script>
<script  id="fragment-shader-2d" type="notjs">

  // fragment shaders don't have a default precision so we need
  // to pick one. mediump is a good default
  precision mediump float;

  void main() {
    // gl_FragColor is a special variable a fragment shader
    // is responsible for setting
    gl_FragColor = vec4(1, 0, 0.5, 1); // return redish-purple
  }

</script><!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="https://webglfundamentals.org/webgl/resources/webgl-utils.js"></script>

/* eslint no-console:0 consistent-return:0 */
"use strict";

function createShader(gl, type, source) {
  var shader = gl.createShader(type);
  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if (success) {
    return shader;
  }

  console.log(gl.getShaderInfoLog(shader));
  gl.deleteShader(shader);
}

function createProgram(gl, vertexShader, fragmentShader) {
  var program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  var success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if (success) {
    return program;
  }

  console.log(gl.getProgramInfoLog(program));
  gl.deleteProgram(program);
}

function main() {
  // Get A WebGL context
  var canvas = document.querySelector("#c");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  // Get the strings for our GLSL shaders
  var vertexShaderSource = document.querySelector("#vertex-shader-2d").text;
  var fragmentShaderSource = document.querySelector("#fragment-shader-2d").text;

  // create GLSL shaders, upload the GLSL source, compile the shaders
  var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
  var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

  // Link the two shaders into a program
  var program = createProgram(gl, vertexShader, fragmentShader);

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");

  // Create a buffer and put three 2d clip space points in it
  var positionBuffer = gl.createBuffer();

  // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  var positions = [
    0, 0,
    0, 0.5,
    0.7, 0,
  ];
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // code above this line is initialization code.
  // code below this line is rendering code.

  webglUtils.resizeCanvasToDisplaySize(gl.canvas);

  // Tell WebGL how to convert from clip space to pixels
  gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

  // Clear the canvas
  gl.clearColor(0, 0, 0, 0);
  gl.clear(gl.COLOR_BUFFER_BIT);

  // Tell it to use our program (pair of shaders)
  gl.useProgram(program);

  // Turn on the attribute
  gl.enableVertexAttribArray(positionAttributeLocation);

  // Bind the position buffer.
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
  var size = 2;          // 2 components per iteration
  var type = gl.FLOAT;   // the data is 32bit floats
  var normalize = false; // don't normalize the data
  var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
  var offset = 0;        // start at the beginning of the buffer
  gl.vertexAttribPointer(
      positionAttributeLocation, size, type, normalize, stride, offset);

  // draw
  var primitiveType = gl.TRIANGLES;
  var offset = 0;
  var count = 3;
  gl.drawArrays(primitiveType, offset, count);
}

main();

var colorUniformLocation = gl.getUniformLocation(program, "u_color");
  ...
 
  // 绘制50个随机颜色矩形
  for (var ii = 0; ii < 50; ++ii) {
    // 创建一个随机矩形
    // 并将写入位置缓冲
    // 因为位置缓冲是我们绑定在
    // `ARRAY_BUFFER`绑定点上的最后一个缓冲
    setRectangle(
        gl, randomInt(300), randomInt(300), randomInt(300), randomInt(300));
 
    // 设置一个随机颜色
    gl.uniform4f(colorUniformLocation, Math.random(), Math.random(), Math.random(), 1);
 
    // 绘制矩形
    gl.drawArrays(gl.TRIANGLES, 0, 6);
  }
}
 
// 返回 0 到 range 范围内的随机整数
function randomInt(range) {
  return Math.floor(Math.random() * range);
}
 
// 用参数生成矩形顶点并写进缓冲
 
function setRectangle(gl, x, y, width, height) {
  var x1 = x;
  var x2 = x + width;
  var y1 = y;
  var y2 = y + height;
 
  // 注意: gl.bufferData(gl.ARRAY_BUFFER, ...) 将会影响到
  // 当前绑定点`ARRAY_BUFFER`的绑定缓冲
  // 目前我们只有一个缓冲，如果我们有多个缓冲
  // 我们需要先将所需缓冲绑定到`ARRAY_BUFFER`
 
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
     x1, y1,
     x2, y1,
     x1, y2,
     x1, y2,
     x2, y1,
     x2, y2]), gl.STATIC_DRAW);
}