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hello-webgl.html
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hello-webgl.html
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<html>
<head>
<title>Hello, WebGL (adopted from Learning WebGL lesson 2)</title>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
varying vec4 vColor;
void main(void) {
gl_FragColor = vColor;
}
</script>
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 positionAttr;
attribute vec4 colorAttr;
varying vec4 vColor;
void main(void) {
gl_Position = vec4(positionAttr, 1.0);
vColor = colorAttr;
}
</script>
<script>
var gl = null;
var viewportWidth = 0;
var viewportHeight = 0;
function initGL(canvas) {
try {
gl = canvas.getContext("webgl");
if (!gl)
gl = canvas.getContext("experimental-webgl");
if (gl) {
viewportWidth = canvas.width;
viewportHeight = canvas.height;
}
} catch (e) {
}
// Not the best error detection logic.
// Redirect to http://get.webgl.org in failure case.
if (!gl) {
alert("Could not initialise WebGL, sorry :-(");
}
}
function getShader(gl, id) {
var script = document.getElementById(id);
if (!script) {
return null;
}
var shader;
if (script.type == "x-shader/x-fragment") {
shader = gl.createShader(gl.FRAGMENT_SHADER);
} else if (script.type == "x-shader/x-vertex") {
shader = gl.createShader(gl.VERTEX_SHADER);
} else {
return null;
}
gl.shaderSource(shader, script.text);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
var program;
function initShaders() {
var vertexShader = getShader(gl, "shader-vs");
var fragmentShader = getShader(gl, "shader-fs");
program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
alert("Could not initialise shaders");
}
gl.useProgram(program);
program.positionAttr = gl.getAttribLocation(program, "positionAttr");
gl.enableVertexAttribArray(program.positionAttr);
program.colorAttr = gl.getAttribLocation(program, "colorAttr");
gl.enableVertexAttribArray(program.colorAttr);
}
var buffer;
function initGeometry() {
buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
// Interleave vertex positions and colors
var vertexData = [
// X Y Z R G B A
0.0, 0.8, 0.0, 1.0, 0.0, 0.0, 1.0,
// X Y Z R G B A
-0.8, -0.8, 0.0, 0.0, 1.0, 0.0, 1.0,
// X Y Z R G B A
0.8, -0.8, 0.0, 0.0, 0.0, 1.0, 1.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertexData), gl.STATIC_DRAW);
}
function drawScene() {
gl.viewport(0, 0, viewportWidth, viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
// There are 7 floating-point values per vertex
var stride = 7 * Float32Array.BYTES_PER_ELEMENT;
// Set up position stream
gl.vertexAttribPointer(program.positionAttr, 3, gl.FLOAT, false, stride, 0);
// Set up color stream
gl.vertexAttribPointer(program.colorAttr, 4, gl.FLOAT, false, stride, 3 * Float32Array.BYTES_PER_ELEMENT);
gl.drawArrays(gl.TRIANGLES, 0, 3);
}
function webGLStart() {
var canvas = document.getElementById("lesson02-canvas");
initGL(canvas);
initShaders()
initGeometry();
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.disable(gl.DEPTH_TEST);
drawScene();
}
</script>
</head>
<body onload="webGLStart();">
A simple example adopted from Giles
Thomas' <a href="http://learningwebgl.com/blog/?p=134">Learning WebGL
Lesson 2</a>. It has been modified to eliminate dependencies on all
external libraries, and to use a single buffer object for all of the
geometric data.
<br>
<br>
<canvas id="lesson02-canvas" style="border: none;" width="500" height="500"></canvas>
</body>
</html>