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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>使用WebGL绘制一个点</title>
</head>
<body>
<!--canvas标签创建一个宽高均为500像素，背景为蓝色的矩形画布-->
<canvas id="webgl" width="400" height="400" style="background-color: blue"></canvas>


<script>
    //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');

    //顶点着色器源码
    var vertexShaderSource = '' +
        'void main(){' +
        //给内置变量gl_PointSize赋值像素大小
        '   gl_PointSize=20.0;' +
        //顶点位置，位于坐标原点
        '   gl_Position =vec4(0.0,0.0,0.0,1.0);' +
        '}';

    //片元着色器源码
    var fragShaderSource = '' +
        'void main(){' +
        //定义片元颜色
        '   gl_FragColor = vec4(1.0,0.0,0.0,1.0);' +
        '}';

    //初始化着色器
    var program = initShader(gl,vertexShaderSource,fragShaderSource);
    //开始绘制，显示器显示结果
    gl.drawArrays(gl.POINTS,0,1);

    //声明初始化着色器函数
    function initShader(gl,vertexShaderSource,fragmentShaderSource){
        //创建顶点着色器对象
        var vertexShader = gl.createShader(gl.VERTEX_SHADER);
        //创建片元着色器对象
        var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
        //引入顶点、片元着色器源代码
        gl.shaderSource(vertexShader,vertexShaderSource);
        gl.shaderSource(fragmentShader,fragmentShaderSource);
        //编译顶点、片元着色器
        gl.compileShader(vertexShader);
        gl.compileShader(fragmentShader);

        //创建程序对象program
        var program = gl.createProgram();
        //附着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);
        //使用program
        gl.useProgram(program);
        //返回程序program对象
        return program;
    }
</script>
</body>
</html>