background/画线矩形.html

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2024-01-13 18:54:32 +00:00
<!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="500" height="500" style="background-color: blue"></canvas>
<script id="vertexShader" type="x-shader/x-vertex">
//attribute声明vec4类型变量apos
attribute vec4 apos;
void main() {
//顶点坐标apos赋值给内置变量gl_Position
//逐顶点处理数据
gl_Position = apos;
}
</script>
<!-- 片元着色器源码 -->
<script id="fragmentShader" type="x-shader/x-fragment">
void main() {
// 逐片元处理数据,所有片元(像素)设置为红色
gl_FragColor = vec4(1.0,0.0,0.0,1.0);
}
</script>
<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');
//初始化着色器
var vertexShaderSource = document.getElementById('vertexShader').innerText;
//片元着色器源码
var fragShaderSource = document.getElementById('fragmentShader').innerText;
//初始化着色器
var program = initShader(gl,vertexShaderSource,fragShaderSource);
//开始绘制,显示器显示结果
//获取顶点着色器的位置变量apos即aposLocation指向apos变量。
var aposLocation = gl.getAttribLocation(program,'apos');
var data=new Float32Array([0.5,0.5,-0.5,0.5,-0.5,-0.5,0.5,-0.5]);
//创建缓冲区对象
var buffer=gl.createBuffer();
//绑定缓冲区对象,激活buffer
gl.bindBuffer(gl.ARRAY_BUFFER,buffer);
//顶点数组data数据传入缓冲区
gl.bufferData(gl.ARRAY_BUFFER,data,gl.STATIC_DRAW);
//缓冲区中的数据按照一定的规律传递给位置变量apos
gl.vertexAttribPointer(aposLocation,2,gl.FLOAT,false,0,0);
//允许数据传递
gl.enableVertexAttribArray(aposLocation);
gl.drawArrays(gl.TRIANGLES,0,4);
//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>