learn-webgl
/
39-2-alphaBlendedCube.html

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<html lang="en">

<head>
  <meta charset="UTF-8">
  <title></title>
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<body>
  <!--通过canvas标签创建一个800px*800px大小的画布-->
  <canvas id="webgl" width="800" height="800"></canvas>
  <script type="text/javascript" src="./lib/cuon-matrix.js"></script>
  <script>
    //顶点着色器
    var VSHADER_SOURCE = '' +
      'attribute vec4 a_Position;\n' + //声明attribute变量a_Position，用来存放顶点位置信息
      'attribute vec4 a_Color;\n' + //声明attribute变量a_Color，用来存放顶点颜色信息
      'uniform mat4 u_MvpMatrix;\n' + //声明uniform变量u_MvpMatrix，用来存放模型视图投影矩阵
      'varying vec4 v_Color;\n' + //声明varying变量v_Color，用来向片元着色器传值顶点颜色信息

      'void main(){\n' +
      '  gl_Position = u_MvpMatrix * a_Position;\n' + //将模型视图投影矩阵和顶点坐标相乘后赋值给顶点着色器内置变量gl_Position
      '  v_Color = a_Color;\n' + //将顶点颜色传给片元着色器
      '}\n'

    //片元着色器
    var FSHADER_SOURCE = '' +
      '#ifdef GL_ES\n' +
      ' precision mediump float;\n' + // 设置精度
      '#endif\n' +
      'varying vec4 v_Color;\n' + //声明varying变量v_Color，用来接收顶点着色器传送的片元颜色信息
      'void main(){\n' +
      '  gl_FragColor = v_Color;\n' + //将顶点着色器传送的片元颜色赋值给内置变量gl_FragColor
      '}\n'

    //初始化着色器函数
    function initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE) {
      //创建顶点着色器对象
      var vertexShader = loadShader(gl, gl.VERTEX_SHADER, VSHADER_SOURCE)
      //创建片元着色器对象
      var fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, FSHADER_SOURCE)

      if (!vertexShader || !fragmentShader) {
        return null
      }

      //创建程序对象program
      var program = gl.createProgram()
      if (!gl.createProgram()) {
        return null
      }
      //分配顶点着色器和片元着色器到program
      gl.attachShader(program, vertexShader)
      gl.attachShader(program, fragmentShader)
      //链接program
      gl.linkProgram(program)

      //检查程序对象是否连接成功
      var linked = gl.getProgramParameter(program, gl.LINK_STATUS)
      if (!linked) {
        var error = gl.getProgramInfoLog(program)
        console.log('程序对象连接失败: ' + error)
        gl.deleteProgram(program)
        gl.deleteShader(fragmentShader)
        gl.deleteShader(vertexShader)
        return null
      }
      //使用program
      gl.useProgram(program)
      gl.program = program
      //返回程序program对象
      return program
    }

    function loadShader(gl, type, source) {
      // 创建顶点着色器对象
      var shader = gl.createShader(type)
      if (shader == null) {
        console.log('创建着色器失败')
        return null
      }

      // 引入着色器源代码
      gl.shaderSource(shader, source)

      // 编译着色器
      gl.compileShader(shader)

      // 检查顶是否编译成功
      var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS)
      if (!compiled) {
        var error = gl.getShaderInfoLog(shader)
        console.log('编译着色器失败: ' + error)
        gl.deleteShader(shader)
        return null
      }

      return shader
    }

    function init() {
      //通过getElementById()方法获取canvas画布
      var canvas = document.getElementById('webgl')

      //通过方法getContext()获取WebGL上下文
      var gl = canvas.getContext('webgl')
      //初始化着色器
      if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
        console.log('初始化着色器失败')
        return
      }

      // 设置canvas的背景色
      gl.clearColor(0, 0, 0, 1)

      //初始化顶点坐标和顶点颜色
      var n = initVertexBuffers(gl)

      setMatrixAndDraw(gl, n)

    }

    //设置矩阵并绘图
    function setMatrixAndDraw(gl, n) {
      //开启混合
      gl.enable(gl.BLEND)
      //设置混合函数
      gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA)

      //清空颜色和深度缓冲区
      gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)

      //获取顶点着色器uniform变量u_MvpMatrix的存储地址
      var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix')
      if (!u_MvpMatrix) {
        console.log('获取uniform变量u_MvpMatrix的存储地址失败')
        return
      }

      //创建、设置模型视图投影矩阵
      var mvpMatrix = new Matrix4()
      mvpMatrix.setPerspective(30, 1, 1, 100)
      mvpMatrix.lookAt(3, 3, 7, 0, 0, 0, 0, 1, 0)


      //给顶点着色器uniform变量u_MvpMatrix传值
      gl.uniformMatrix4fv(u_MvpMatrix, false, mvpMatrix.elements)

      //透明与不透明物体共存
      gl.enable(gl.DEPTH_TEST) //开启隐藏面消除
      gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0) //绘制立方体最前面的不透明的面
      gl.depthMask(false) //锁定用于进行隐藏面消除的深度缓冲区，使之只读
      gl.drawElements(gl.TRIANGLES, n - 6, gl.UNSIGNED_BYTE, 6 * g_FSIZE) //绘制其余半透明的面
      gl.depthMask(true) //释放深度缓冲区，使之可读可写

    }
    var g_FSIZE = 0
    //初始化顶点坐标和顶点颜色
    function initVertexBuffers(gl) {

      var v0 = [1.0, 1.0, 1.0]
      var v1 = [-1.0, 1.0, 1.0]
      var v2 = [-1.0, -1.0, 1.0]
      var v3 = [1.0, -1.0, 1.0]
      var v4 = [1.0, -1.0, -1.0]
      var v5 = [1.0, 1.0, -1.0]
      var v6 = [-1.0, 1.0, -1.0]
      var v7 = [-1.0, -1.0, -1.0]

      //顶点
      var vertices = new Float32Array([
        ...v0, ...v1, ...v2, ...v3, // 前
        ...v0, ...v3, ...v4, ...v5, // 右
        ...v0, ...v5, ...v6, ...v1, // 上
        ...v1, ...v6, ...v7, ...v2, // 左
        ...v7, ...v4, ...v3, ...v2, // 下
        ...v4, ...v7, ...v6, ...v5 // 后
      ])

      var fontColor = [0.5, 0.5, 1.0, 1.0]
      var backColor = [0.5, 1.0, 1.0, 0.4]
      var leftColor = [1.0, 1.0, 0.5, 0.4]
      var rightColor = [0.5, 1.0, 0.5, 0.2]
      var topColor = [1.0, 0.5, 0.5, 0.2]
      var downColor = [1.0, 1.0, 1.0, 0.2]
      // 顶点的颜色
      var colors = new Float32Array([
        ...fontColor, ...fontColor, ...fontColor, ...fontColor, // v0-v1-v2-v3 前
        ...rightColor, ...rightColor, ...rightColor, ...rightColor, // v0-v3-v4-v5 右
        ...topColor, ...topColor, ...topColor, ...topColor, // v0-v5-v6-v1 上
        ...leftColor, ...leftColor, ...leftColor, ...leftColor, // v1-v6-v7-v2 左
        ...downColor, ...downColor, ...downColor, ...downColor, // v7-v4-v3-v2 下
        ...backColor, ...backColor, ...backColor, ...backColor, // v4-v7-v6-v5 后
      ])

      // 绘制的索引
      var indices = new Uint8Array([
        0, 1, 2, 0, 2, 3, // 前
        4, 5, 6, 4, 6, 7, // 右
        8, 9, 10, 8, 10, 11, // 上
        12, 13, 14, 12, 14, 15, // 左
        16, 17, 18, 16, 18, 19, // 下
        20, 21, 22, 20, 22, 23 // 后
      ])

      g_FSIZE = indices.BYTES_PER_ELEMENT

      if (!initArrayBuffer(gl, vertices, 3, gl.FLOAT, 'a_Position')) {
        return -1
      }

      if (!initArrayBuffer(gl, colors, 4, gl.FLOAT, 'a_Color')) {
        return -1
      }

      //创建缓冲区对象
      var indexBuffer = gl.createBuffer()

      //将顶点索引写入缓冲区对象
      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer)
      gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW)

      return indices.length

    }

    function initArrayBuffer(gl, data, num, type, attribute) {
      //创建缓冲区对象
      var buffer = gl.createBuffer()
      //将顶点坐标和顶点颜色信息写入缓冲区对象
      gl.bindBuffer(gl.ARRAY_BUFFER, buffer)
      gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW)

      //获取顶点着色器attribute变量存储地址, 分配缓存并开启
      var a_Attribute = gl.getAttribLocation(gl.program, attribute)
      gl.vertexAttribPointer(a_Attribute, num, type, false, 0, 0)
      gl.enableVertexAttribArray(a_Attribute)

      return true
    }

    init()
  </script>
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