multiAttributeColor.js

//顶点着色器-分号是必要的
var VSHADER_SOURCE = 
"attribute vec4 a_Position; \n" +
"attribute vec4 a_Color; \n" +
"varying vec4 v_Color; \n" + //varying变量
"void main() { \n" +
"gl_Position = a_Position;\n" +
"gl_PointSize = 10.0;\n" +
"v_Color = a_Color;\n" +
"}\n";

//片元着色器-使用变量时需要定义精度
var FSHADER_SOURCE =
  "precision mediump float;\n" +
  "varying vec4 v_Color;\n" + 
  "void main() { \n" + 
  "gl_FragColor = v_Color; \n" + 
  "}\n";

function main() {
  //获取canvas元素
  var canvas = document.getElementById("webgl");
  //获取WebGL绘图上下文
  var gl = getWebGLContext(canvas);
  //初始化着色器
  initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE);

  //设置顶点坐标和颜色
  var n = initVertexBuffers(gl);
  //设置canvas的背景色
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  //清空canvas
  gl.clear(gl.COLOR_BUFFER_BIT);
  
  //绘制点
  //gl.drawArrays(gl.POINT, 0, n);
  //绘制三角形
  gl.drawArrays(gl.TRIANGLES, 0, n);
}

function initVertexBuffers(gl) {
    var verticesColors = new Float32Array([
        0.0,0.5,1.0,0.0,0.0,
        -0.5,-0.5,0.0,1.0,0.0,
        0.5,-0.5,0.0,0.0,1.0
      ]);
    var n = 3; //点的个数
  
    //创建缓冲区对象
    var vertexColorBuffer = gl.createBuffer();
  
    //将缓冲区对象绑定到目标
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
    //向缓冲区对象中写入数据
    gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);
  
    var FSIZE = verticesColors.BYTES_PER_ELEMENT;
  
    //获取attribute变量a_Position的存储位置
    var a_Position = gl.getAttribLocation(gl.program, "a_Position");
  
    //将缓冲区对象分配给a_Position变量
    gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, FSIZE * 5, 0);
    //连接a_Position变量与分配给他的缓冲区对象
    gl.enableVertexAttribArray(a_Position);

    //获取a_Color的存储位置，分配缓冲区并开启
    var a_Color = gl.getAttribLocation(gl.program, 'a_Color')
  
    //将缓冲区对象分配给a_Position变量
    gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 5, FSIZE * 2);
    //连接a_Position变量与分配给他的缓冲区对象
    gl.enableVertexAttribArray(a_Color);
  
    return n;
  }