WebGL简易教程(十一)：纹理

基于《WebGL简易教程(九)：综合实例：地形的绘制》中的JS代码进行改进：

// 顶点着色器程序507383170
var VSHADER_SOURCE =
  ‘attribute vec4 a_Position;\n‘ + //位置
  ‘attribute vec4 a_Color;\n‘ + //颜色
  ‘uniform mat4 u_MvpMatrix;\n‘ +
  ‘varying vec4 v_Color;\n‘ +
  ‘varying vec4 v_position;\n‘ +
  ‘void main() {\n‘ +
  ‘  v_position = a_Position;\n‘ +
  ‘  gl_Position = u_MvpMatrix * a_Position;\n‘ + // 设置顶点坐标
  ‘  v_Color = a_Color;\n‘ +
  ‘}\n‘;

// 片元着色器程序
var FSHADER_SOURCE =
  ‘precision mediump float;\n‘ +
  ‘uniform vec2 u_RangeX;\n‘ + //X方向范围
  ‘uniform vec2 u_RangeY;\n‘ + //Y方向范围
  ‘uniform sampler2D u_Sampler;\n‘ +
  ‘varying vec4 v_Color;\n‘ +
  ‘varying vec4 v_position;\n‘ +
  ‘void main() {\n‘ +
  ‘  vec2 v_TexCoord = vec2((v_position.x-u_RangeX[0]) / (u_RangeX[1]-u_RangeX[0]), 1.0-(v_position.y-u_RangeY[0]) / (u_RangeY[1]-u_RangeY[0]));\n‘ +
  ‘  gl_FragColor = texture2D(u_Sampler, v_TexCoord);\n‘ +
  ‘}\n‘;

//定义一个矩形体：混合构造函数原型模式
function Cuboid(minX, maxX, minY, maxY, minZ, maxZ) {
  this.minX = minX;
  this.maxX = maxX;
  this.minY = minY;
  this.maxY = maxY;
  this.minZ = minZ;
  this.maxZ = maxZ;
}

Cuboid.prototype = {
  constructor: Cuboid,
  CenterX: function () {
    return (this.minX + this.maxX) / 2.0;
  },
  CenterY: function () {
    return (this.minY + this.maxY) / 2.0;
  },
  CenterZ: function () {
    return (this.minZ + this.maxZ) / 2.0;
  },
  LengthX: function () {
    return (this.maxX - this.minX);
  },
  LengthY: function () {
    return (this.maxY - this.minY);
  }
}

//定义DEM
function Terrain() { }
Terrain.prototype = {
  constructor: Terrain,
  setWH: function (col, row) {
    this.col = col;
    this.row = row;
  }
}

var currentAngle = [0.0, 0.0]; // 绕X轴Y轴的旋转角度 ([x-axis, y-axis])
var curScale = 1.0; //当前的缩放比例
var initTexSuccess = false; //纹理图像是否加载完成

function main() {
  var demFile = document.getElementById(‘demFile‘);
  if (!demFile) {
    console.log("Failed to get demFile element!");
    return;
  }

  //加载文件后的事件
  demFile.addEventListener("change", function (event) {
    //判断浏览器是否支持FileReader接口
    if (typeof FileReader == ‘undefined‘) {
      console.log("你的浏览器不支持FileReader接口！");
      return;
    }

    //读取文件后的事件
    var reader = new FileReader();
    reader.onload = function () {
      if (reader.result) {
        var terrain = new Terrain();
        if (!readDEMFile(reader.result, terrain)) {
          console.log("文件格式有误，不能读取该文件！");
        }

        //绘制函数
        onDraw(gl, canvas, terrain);
      }
    }

    var input = event.target;
    reader.readAsText(input.files[0]);
  });

  // 获取 <canvas> 元素
  var canvas = document.getElementById(‘webgl‘);

  // 获取WebGL渲染上下文
  var gl = getWebGLContext(canvas);
  if (!gl) {
    console.log(‘Failed to get the rendering context for WebGL‘);
    return;
  }

  // 初始化着色器
  if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
    console.log(‘Failed to intialize shaders.‘);
    return;
  }

  // 指定清空<canvas>的颜色
  gl.clearColor(0.0, 0.0, 0.0, 1.0);

  // 开启深度测试
  gl.enable(gl.DEPTH_TEST);

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

//绘制函数
function onDraw(gl, canvas, terrain) {
  // 设置顶点位置
  //var cuboid = new Cuboid(399589.072, 400469.072, 3995118.062, 3997558.062, 732, 1268); 
  var n = initVertexBuffers(gl, terrain);
  if (n < 0) {
    console.log(‘Failed to set the positions of the vertices‘);
    return;
  }

  //设置纹理
  if (!initTextures(gl, terrain)) {
    console.log(‘Failed to intialize the texture.‘);
    return;
  }

  //注册鼠标事件
  initEventHandlers(canvas);

  //绘制函数
  var tick = function () {
    if (initTexSuccess) {
      //设置MVP矩阵
      setMVPMatrix(gl, canvas, terrain.cuboid);

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

      //绘制矩形体
      gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_SHORT, 0);
      //gl.drawArrays(gl.Points, 0, n);
    }

    //请求浏览器调用tick
    requestAnimationFrame(tick);
  };

  //开始绘制
  tick();
}

function initTextures(gl, terrain) {
  // 传递X方向和Y方向上的范围到着色器
  var u_RangeX = gl.getUniformLocation(gl.program, ‘u_RangeX‘);
  var u_RangeY = gl.getUniformLocation(gl.program, ‘u_RangeY‘);
  if (!u_RangeX || !u_RangeY) {
    console.log(‘Failed to get the storage location of u_RangeX or u_RangeY‘);
    return;
  }
  gl.uniform2f(u_RangeX, terrain.cuboid.minX, terrain.cuboid.maxX);
  gl.uniform2f(u_RangeY, terrain.cuboid.minY, terrain.cuboid.maxY);

  //创建一个image对象
  var image = new Image();
  if (!image) {
    console.log(‘Failed to create the image object‘);
    return false;
  }
  //图像加载的响应函数 
  image.onload = function () {
    if (loadTexture(gl, image)) {
      initTexSuccess = true;
    }
  };

  //浏览器开始加载图像
  image.src = ‘tex.jpg‘;

  return true;
}

function loadTexture(gl, image) {
  // 创建纹理对象
  var texture = gl.createTexture();
  if (!texture) {
    console.log(‘Failed to create the texture object‘);
    return false;
  }

  // 开启0号纹理单元
  gl.activeTexture(gl.TEXTURE0);
  // 绑定纹理对象
  gl.bindTexture(gl.TEXTURE_2D, texture);

  // 设置纹理参数
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);

  // 配置纹理图像
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, gl.RGB, gl.UNSIGNED_BYTE, image);

  // 将0号单元纹理传递给着色器中的取样器变量 
  var u_Sampler = gl.getUniformLocation(gl.program, ‘u_Sampler‘);
  if (!u_Sampler) {
    console.log(‘Failed to get the storage location of u_Sampler‘);
    return false;
  }
  gl.uniform1i(u_Sampler,