前言

WebGL（全写Web Graphics Library）是一种3D绘图协议，这种绘图技术标准允许把JavaScript和OpenGL ES 2.0结合在一起，通过增加OpenGL ES 2.0的一个JavaScript绑定，WebGL可以为HTML5 Canvas提供硬件3D加速渲染，这样Web开发人员就可以借助系统显卡来在浏览器里更流畅地展示3D场景和模型了，还能创建复杂的导航和数据视觉化。显然，WebGL技术标准免去了开发网页专用渲染插件的麻烦，可被用于创建具有复杂3D结构的网站页面，甚至可以用来设计3D网页游戏等等。–百度百科

在现实中webgl的用途很多，比如医院运维网站，地铁运维网站，海绵城市，可以以三维网页形式展示出现实状态。

WebGL相关文档：http://doc.yonyoucloud.com/doc/wiki/project/webgl/webgL-fundamentals.html

一、webgl的使用

安装第三方包：npm i --save threejs-miniprogram

1.画正方形

import drawRectangle from './draw-rectangle'


Page({

  /**
   * 页面的初始数据
   */
  data: {

  },

  /**
   * 生命周期函数--监听页面加载
   */
  onLoad: function (options) {

  },

  /**
   * 生命周期函数--监听页面初次渲染完成
   */
  onReady: function () {
    wx.createSelectorQuery()
      .select('#myCanvas1')
      .node()
      .exec((res) => {
        const canvas = res[0].node
        const gl = canvas.getContext('webgl')
        if (!gl) {
          console.log('webgl未受支持');
          return
        }
        // 检查所有支持的扩展
        var available_extensions = gl.getSupportedExtensions();
        console.log(available_extensions);

        // 清除画布
        // 使用完全不透明的黑色清除所有图像，我们将清除色设为黑色，此时并没有开始清除
        gl.clearColor(0.0, 0.0, 0.0, 1.0);
        // 用上面指定的颜色清除缓冲区
        gl.clear(gl.COLOR_BUFFER_BIT);

        // 画的是一个正方形
        drawRectangle(gl)
})

import {
  mat4
} from '../../lib/gl-matrix'


function drawColorRectangle(gl) {

  // Vertex shader program

  const vsSource = `
    attribute vec4 aVertexPosition;
    attribute vec4 aVertexColor;
    uniform mat4 uModelViewMatrix;
    uniform mat4 uProjectionMatrix;
    varying lowp vec4 vColor;
    void main(void) {
      gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;
      vColor = aVertexColor;
    }`;

  // Fragment shader program

  // 每个片段只是根据其相对于顶点的位置得到一个插值过的颜色，而不是一个指定的颜色值。
  // lowp表示低精度
  // lowp, mediump和highp
  const fsSource = `
    varying lowp vec4 vColor;
    void main(void) {
      gl_FragColor = vColor;
    }`;

  // Initialize a shader program; this is where all the lighting
  // for the vertices and so forth is established.
  const shaderProgram = initShaderProgram(gl, vsSource, fsSource);

  // Collect all the info needed to use the shader program.
  // Look up which attributes our shader program is using
  // for aVertexPosition, aVevrtexColor and also
  // look up uniform locations.
  const programInfo = {
    program: shaderProgram,
    attribLocations: {
      vertexPosition: gl.getAttribLocation(shaderProgram, 'aVertexPosition'),
      vertexColor: gl.getAttribLocation(shaderProgram, 'aVertexColor'),
    },
    uniformLocations: {
      projectionMatrix: gl.getUniformLocation(shaderProgram, 'uProjectionMatrix'),
      modelViewMatrix: gl.getUniformLocation(shaderProgram, 'uModelViewMatrix'),
    },
  };

  // Here's where we call the routine that builds all the
  // objects we'll be drawing.
  const buffers = initBuffers(gl);

  // Draw the scene
  drawScene(gl, programInfo, buffers);
}

//
// initBuffers
//
// Initialize the buffers we'll need. For this demo, we just
// have one object -- a simple two-dimensional square.
//
function initBuffers(gl) {

  // Create a buffer for the square's positions.

  const positionBuffer = gl.createBuffer();

  // Select the positionBuffer as the one to apply buffer
  // operations to from here out.

  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

  // Now create an array of positions for the square.

  const positions = [
    1.0,  1.0,  0.0,
    -1.0, 1.0,  0.0,
    1.0,  -1.0, 0.0,
    -1.0, -1.0, 0.0
  ];

  // Now pass the list of positions into WebGL to build the
  // shape. We do this by creating a Float32Array from the
  // JavaScript array, then use it to fill the current buffer.

  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

  // Now set up the colors for the vertices

  // 此数组中包含四组四值向量，每一组向量代表一个顶点的颜色。
var colors = [
  1.0,  1.0,  1.0,  1.0,    // white
  1.0,  0.0,  0.0,  1.0,    // red
  0.0,  1.0,  0.0,  1.0,    // green
  0.0,  0.0,  1.0,  1.0,    // blue
];

  const colorBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);

  return {
    position: positionBuffer,
    color: colorBuffer,
  };
}

//
// Draw the scene.
//
function drawScene(gl, programInfo, buffers) {
  gl.clearColor(0.0, 0.0, 0.0, 1.0);  // Clear to black, fully opaque
  gl.clearDepth(1.0);                 // Clear everything
  gl.enable(gl.DEPTH_TEST);           // Enable depth testing
  gl.depthFunc(gl.LEQUAL);            // Near things obscure far things

  // Clear the canvas before we start drawing on it.

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

  // Create a perspective matrix, a special matrix that is
  // used to simulate the distortion of perspective in a camera.
  // Our field of view is 45 degrees, with a width/height
  // ratio that matches the display size of the canvas
  // and we only want to see objects between 0.1 units
  // and 100 units away from the camera.

  const fieldOfView = 45 * Math.PI / 180;   // in radians
  const aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
  const zNear = 0.1;
  const zFar = 100.0;
  const projectionMatrix = mat4.create();

  // note: glmatrix.js always has the first argument
  // as the destination to receive the result.
  mat4.perspective(projectionMatrix,
                   fieldOfView,
                   aspect,
                   zNear,
                   zFar);

  // Set the drawing position to the "identity" point, which is
  // the center of the scene.
  const modelViewMatrix = mat4.create();

  // Now move the drawing position a bit to where we want to
  // start drawing the square.

  mat4.translate(modelViewMatrix,     // destination matrix
                 modelViewMatrix,     // matrix to translate
                 [-0.0, 0.0, -6.0]);  // amount to translate

  // Tell WebGL how to pull out the positions from the position
  // buffer into the vertexPosition attribute
  {
    const numComponents = 3;
    const type = gl.FLOAT;
    const normalize = false;
    const stride = 0;
    const offset = 0;
    gl.bindBuffer(gl.ARRAY_BUFFER, buffers.position);

    gl.vertexAttribPointer(
        programInfo.attribLocations.vertexPosition,
        numComponents,
        type,
        normalize,
        stride,
        offset);
        
    gl.enableVertexAttribArray(
        programInfo.attribLocations.vertexPosition);
  }

  // Tell WebGL how to pull out the colors from the color buffer
  // into the vertexColor attribute.
  {
    const numComponents = 4;
    const type = gl.FLOAT;
    const normalize = false;
    const stride = 0;
    const offset = 0;

    gl.bindBuffer(gl.ARRAY_BUFFER, buffers.color);


  gl.vertexAttribPointer(
    programInfo.attribLocations.vertexColor,
    numComponents,
    type,
    normalize,
    stride,
    offset);

    gl.enableVertexAttribArray(
      programInfo.attribLocations.vertexColor);
    }

  // Tell WebGL to use our program when drawing

  gl.useProgram(programInfo.program);

  // Set the shader uniforms

  gl.uniformMatrix4fv(
      programInfo.uniformLocations.projectionMatrix,
      false,
      projectionMatrix);

  gl.uniformMatrix4fv(
      programInfo.uniformLocations.modelViewMatrix,
      false,
      modelViewMatrix);

  {
    const offset = 0;
    const vertexCount = 4;
    gl.drawArrays(gl.TRIANGLE_STRIP, offset, vertexCount);
  }
}

//
// Initialize a shader program, so WebGL knows how to draw our data
//
function initShaderProgram(gl, vsSource, fsSource) {
  const vertexShader = loadShader(gl, gl.VERTEX_SHADER, vsSource);
  const fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fsSource);

  // Create the shader program

  const shaderProgram = gl.createProgram();
  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);

  // If creating the shader program failed, alert

  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
    alert('Unable to initialize the shader program: ' + gl.getProgramInfoLog(shaderProgram));
    return null;
  }

  return shaderProgram;
}

//
// creates a shader of the given type, uploads the source and
// compiles it.
//
function loadShader(gl, type, source) {
  const shader = gl.createShader(type);

  // Send the source to the shader object

  gl.shaderSource(shader, source);

  // Compile the shader program

  gl.compileShader(shader);

  // See if it compiled successfully

  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    alert('An error occurred compiling the shaders: ' + gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
    return null;
  }

  return shader;
}

export default drawColorRectangle

实际效果

二、相关包源码

gl-matrix相关包源码链接如下：
https://download.csdn.net/download/aa2528877987/86513333

三、总结

画一个图形主要经历如下四个步骤：

• 1.编写GLSL着色器代码，一个是顶点着色器，一个是片断着色器。
• 2.加载着色器，组成着色器程序。
• 3.创建缓冲区对象，填充缓冲区。
• 4.创建摄像机透视距阵，把元件放到适当的位置。
• 5.给着色器中的变量绑定值。
• 6.调用gl.drawArrays，从向量数组中开始绘制。