WebGl高级编程--创建基本的WebGL示例
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2022-03-10 17:07:31
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<!DOCTYPE HTML>
<html lang="en">
<head>
<title> Load Shaders From DOM</title>
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;
void main() {
gl_Position = vec4(aVertexPosition, 3.1);//Z 坐标
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
void main() {
gl_FragColor = vec4(0.0, 0.0, 1.0, 0.5);//决定三角形颜色
}
</script>
<script src="webgl-debug.js"></script>
<script type="text/javascript">
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 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;//返回某个元素之后紧跟的节点:
}
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 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 setupBuffers() {
vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
var triangleVertices = [
0.0, 0.5, 4,//z坐标为4，此时少了一块，与gl_Position = vec4(aVertexPosition, 3.1);//Z 坐标有关
-0.5, -0.5, 1.0,
0.5, -0.5, 1.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
vertexBuffer.itemSize = 3;
vertexBuffer.numberOfItems = 3;
}
function draw() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
vertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.numberOfItems);
}
function startup() {
canvas = document.getElementById("WebGLCanvas");
gl = WebGLDebugUtils.makeDebugContext(createGLContext(canvas));
setupShaders();
setupBuffers();
gl.clearColor(1.0, 0.0, 0.0, 0.5);//可改变背景颜色
draw();
}
</script>
</head>
<body οnlοad="startup();">
<canvas id = "WebGLCanvas" width="500" height="500"></canvas>
</body>
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