<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>WebGL</title>
<!-- 顶点着色器 -->
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;
void main() {
gl_Position = vec4(aVertexPosition, 1.0);
}
</script>
<!-- 片段着色器 -->
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
void main() {
gl_FragColor = vec4(0, 1.0, 1.0, 1.0);
}
</script>
<script>
var gl;
var canvas;
var shaderProgram;
var vertexBuffer;
function createGLContext(canvas) {
var names = ["webgl", "experimental-webgl"];
var context = null;
for (var i = 0; i < names.length; i++) {
try {
context = canvas.getContext(names[i]);
} catch (e) { }
if (context) {
break;
}
}
if (context) {
context.viewportWidth = canvas.width;
context.viewportHeight = canvas.height;
} else {
alert("Failed to create WebGL context!");
}
return context;
}
function setupShaders() {
vertexShader = loadShaderFromDOM("shader-vs");
fragmentShader = loadShaderFromDOM("shader-fs");
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Failed to setup shaders");
}
gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
}
function loadShaderFromDOM(id) {
var shaderScript = document.getElementById(id);
if (!shaderScript) {
return null;
}
var shaderSource = "";
var currentChild = shaderScript.firstChild;
while (currentChild) {
if (currentChild.nodeType == 3) {
shaderSource += currentChild.textContent;
}
currentChild = currentChild.nextSibling;
}
var shader;
if (shaderScript.type == "x-shader/x-fragment") {
shader = gl.createShader(gl.FRAGMENT_SHADER);
} else if (shaderScript.type == "x-shader/x-vertex") {
shader = gl.createShader(gl.VERTEX_SHADER);
} else {
return null;
}
gl.shaderSource(shader, shaderSource);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
function setupBuffers() {
vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
var triangleVertices = [
-0.5, 0.5, 0.0,0.0,0.0,0.0,
0.5, 0.5, 0.0,0.0,0.0,0.0,
0.5, -0.5, 0.0,0.0,0.0,0.0,
-0.5, 0.5, 0.0,0.0,0.0,0.0,
0.5, -0.5, 0.0,0.0,0.0,0.0,
-0.5, -0.5, 0.0,0.0,0.0,0.0,
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
}
function draw() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 3, gl.FLOAT, false, 4*6, 0);
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
gl.drawArrays(gl.TRIANGLES, 0, 6);
}
function startup() {
canvas = document.getElementById("myGLCanvas");
gl = createGLContext(canvas);
setupShaders();
setupBuffers();
gl.clearColor(0.8, 0.4, 0.0, 0.5);
draw();
}
</script>
</head>
<body onload="startup();">
<canvas id="myGLCanvas" width="500" height="500"></canvas>
</body>
</html>
