WebGl 一个缓冲区传递颜色和坐标（矩形）
效果：
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>WebGl 一个缓冲区传递颜色和坐标（矩形）</title>
</head>
<body>
<canvas id="myCanvas" width="500" height="300" style='border:1px solid red'></canvas>
</body>
<script>
window.onload = function () {
//获取上下文
var canvas = document.getElementById('myCanvas');
var gl = canvas.getContext('webgl');
//定义矩形数据 并 将其储存在缓存对象
var vertices = [
-0.5,0.5,0.0, 0.0,0.0,1.0,//(x,y,z)(r,g,b)分别代表坐标和颜色
-0.5,-0.5,0.0, 1.0,0.0,0.0,
0.5,-0.5,0.0, 0.0,1.0,0.0,
0.5,0.5,0.0, 1.0,0.0,1.0,
];
var indices = [3,2,1,3,1,0];
var vertex_buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER,vertex_buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
var Index_Buffer = gl.createBuffer();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER,Index_Buffer);//注意 是 ELEMENT_ARRAY_BUFFER 不是 ARRAY_BUFFER
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STATIC_DRAW);
//bufferData 参数详解
//数据类型，可以是 gl.ARRAY_BUFFER , gl.ELEMENT_ARRAY_BUFFER
//数据
//缓冲类型，有这么几种可以供我们选择 GL_STREAM_DRAW , GL_STATIC_DRAW ,GL_DYNAMIC_DRAW
//缓冲区的数据偶尔变动用GL_STREAM_DRAW ，缓冲区的数据不变用GL_STATIC_DRAW，缓冲区数据经常变动用GL_DYNAMIC_DRAW
//创建和编译着色器程序
var vertCode = 'attribute vec3 coordinates;'+
'attribute vec3 color;'+
'varying vec3 vColor;'+
'void main(void) {' +
' gl_Position = vec4(coordinates, 1.0);' +
'vColor = color;'+
'}';
var fragCode = 'precision mediump float;'+
'varying vec3 vColor;'+
'void main(void) {'+
'gl_FragColor = vec4(vColor, 1.0);'+
'}';
var vertShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertShader, vertCode);
gl.compileShader(vertShader);
var fragShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragShader, fragCode);
gl.compileShader(fragShader);
var shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertShader);
gl.attachShader(shaderProgram, fragShader);
gl.linkProgram(shaderProgram);
gl.useProgram(shaderProgram);
//与缓冲区对象相关联着色器程序
// vertices中每个元素的字节数 ,这里是 float 类型, 所以是 4 个字节
var bytes = new Float32Array(vertices).BYTES_PER_ELEMENT;
var coord = gl.getAttribLocation(shaderProgram, "coordinates");
gl.vertexAttribPointer(coord, 3, gl.FLOAT, false, bytes*6, 0);
gl.enableVertexAttribArray(coord);
var color = gl.getAttribLocation(shaderProgram, "color");
gl.vertexAttribPointer(color, 3, gl.FLOAT, false, bytes*6, bytes*3) ;
gl.enableVertexAttribArray(color);
//绘制所需的对象
gl.clearColor(0.5, 0.5, 0.5, 0.9);
gl.enable(gl.DEPTH_TEST);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.viewport(0,0,canvas.width,canvas.height);
gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT,0);
}
// vertexAttribPointer(location, int size, enum type, bool normalized, long stride, long offset) 参数详解
//Location − 它指定一个属性变量的存储位置。根据这个方案，必须通过由getAttribLocation()方法返回的值
//Size − 它指定在缓冲对象每顶点部件的数量
//Type − 它指定数据的类型
//Normalized − 这是一个布尔值。如果为真，非浮动数据被归一化到[0,1]。否则，它被归一化到[-1,1]
//Stride − 它指定不同顶点数据元素之间的字节数，或默认为零步幅（字节）
//Offset − 它指定在缓冲器对象，以指示数据从顶点的哪个存储字节偏移(字节)
</script>
</html>
