1. /* eslint no-console:0 consistent-return:0 */
    2. "use strict";  /* 严格模式 */
    4. /* 
    5.  *** 创建对应的类型的着色器
    6.  *** gl === 渲染上下文
    7.  *** type === 着色器类型  
    8.  *** source === 数据源
    9. */
    11. function createShader(gl, type, source) {
    12.   var shader = gl.createShader(type); // 创建着色器对象
    13.   gl.shaderSource(shader, source); // 提供数据源
    14.   gl.compileShader(shader); // 编译 -> 生成着色器
    15.   var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
    16.   if (success) {
    17.     return shader;
    18.   }
    20.   console.log(gl.getShaderInfoLog(shader));
    21.   gl.deleteShader(shader);
    22. }
    24. /* 
    25.  *** 创建渲染程序
    26.  *** gl === 渲染上下文
    27.  *** type === 着色器类型  
    28.  *** source === 数据源
    29. */
    31. function createProgram(gl, vertexShader, fragmentShader) {
    32.   var program = gl.createProgram();
    33.   gl.attachShader(program, vertexShader);
    34.   gl.attachShader(program, fragmentShader);
    35.   gl.linkProgram(program);
    36.   var success = gl.getProgramParameter(program, gl.LINK_STATUS);
    37.   if (success) {
    38.     return program;
    39.   }
    40.   console.log(gl.getProgramInfoLog(program));
    41.   gl.deleteProgram(program);
    42. }
    46. function main() {
    48.   // Get A WebGL context 获取对应的绘制上下文 canvas 
    49.   var canvas = document.querySelector("#c");
    50.   var gl = canvas.getContext("webgl");
    51.   if (!gl) {
    52.     return;
    53.   }
    55.   // Get the strings for our GLSL shaders 获取对应的glsl程序的数据
    56.   var vertexShaderSource = document.querySelector("#vertex-shader-2d").text;
    57.   var fragmentShaderSource = document.querySelector("#fragment-shader-2d").text;
    59.   // create GLSL shaders, upload the GLSL source, compile the shaders 创建对应的着色器
    60.   var vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
    61.   var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
    63.   // Link the two shaders into a program  建立渲染程序
    64.   var program = createProgram(gl, vertexShader, fragmentShader);
    66.   // look up where the vertex data needs to go  把对应的定点传入到对应的程序
    67.   var positionAttributeLocation = gl.getAttribLocation(program, "a_position");
    69.   // 如果从js的一遍遍的向程序添加数据的话；单线程会导致在大量数据的情况会比较卡和缓慢 所以在利用gpu的多线程并行渲染的能力就可以
    70.   // 而GPU的数据是从对应的内存缓存中去（ butter ）
    71.   // Create a buffer and put three 2d clip space points in it
    72.   var positionBuffer = gl.createBuffer();
    74.   // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer) 绑定对应的类型
    75.   gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
    77.   var positions = [
    78.     0, 0,
    79.     0, 0.5,
    80.     0.7, 0,
    81.   ];
    83.   // 绑定对应的强类型的点到缓存的类型数据上去
    84.   gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);
    86.   // code above this line is initialization code.
    87.   // code below this line is rendering code.
    89.   webglUtils.resizeCanvasToDisplaySize(gl.canvas);
    91.   // Tell WebGL how to convert from clip space to pixels 设置对应的视窗效果
    92.   gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
    94.   // Clear the canvas 清空画布
    95.   gl.clearColor(0, 0, 0, 0);
    96.   gl.clear(gl.COLOR_BUFFER_BIT);
    98.   // Tell it to use our program (pair of shaders) 使用渲染程序
    99.   gl.useProgram(program);
    101.   // Turn on the attribute   激活变量 
    102.   gl.enableVertexAttribArray(positionAttributeLocation);
    104.   // Bind the position buffer. 又来一遍？
    105.   gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
    107.   // Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER) 告诉属性怎么从positionBuffer中缓存中读取数据 
    109.   var size = 2;          // 2 components per iteration 每次迭代运行提取两个单位数据
    110.   var type = gl.FLOAT;   // the data is 32bit floats  每个单位的数据类型是32位浮点型
    111.   var normalize = false; // don't normalize the data  不需要归一化数据
    112.   var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position  0 = 移动单位数量 * 每个单位占用内存（sizeof(type)）
    113.   var offset = 0;        // start at the beginning of the buffer 
    115.   gl.vertexAttribPointer positionAttributeLocation, size, type, normalize, stride, offset); 
    117.   // draw
    118.   var primitiveType = gl.TRIANGLES;
    119.   var offset = 0;
    120.   var count = 3;
    121.   gl.drawArrays(primitiveType, offset, count);
    123. }
    125. // 开始启动
    126. main();
    129. // Html
    130. <canvas id="c"></canvas>
    131.   <script  id="vertex-shader-2d" type="notjs">
    133.   // an attribute will receive data from a buffer
    134.   attribute vec4 a_position;
    136.   // all shaders have a main function
    137.   void main() {
    139.     // gl_Position is a special variable a vertex shader
    140.     // is responsible for setting
    141.     gl_Position = a_position;
    142.   }
    144. </script>
    146. <script  id="fragment-shader-2d" type="notjs">
    148.   // fragment shaders don't have a default precision so we need
    149.   // to pick one. mediump is a good default
    150.   precision mediump float;
    152.   void main() {
    153.     // gl_FragColor is a special variable a fragment shader
    154.     // is responsible for setting
    155.     gl_FragColor = vec4(1, 0, 0.5, 1); // return redish-purple
    156.   }
    158. </script>
    160. <!--
    161. for most samples webgl-utils only provides shader compiling/linking and
    162. canvas resizing because why clutter the examples with code that's the same in every sample.
    163. See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
    164. and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
    165. for webgl-utils, m3, m4, and webgl-lessons-ui.
    166. -->
    168. <script src="https://webglfundamentals.org/webgl/resources/webgl-utils.js"></script>