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<html>
<head>
<title>Learning WebGL &mdash; lesson 9</title>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<script type="text/javascript" src="glMatrix-0.9.5.min.js"></script>
<script type="text/javascript" src="webgl-utils.js"></script>
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
varying vec2 vTextureCoord;
uniform sampler2D uSampler;
uniform vec3 uColor;
void main(void) {
vec4 textureColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
gl_FragColor = textureColor * vec4(uColor, 1.0);
}
</script>
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;
attribute vec2 aTextureCoord;
uniform mat4 uMVMatrix;
uniform mat4 uPMatrix;
varying vec2 vTextureCoord;
void main(void) {
gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
vTextureCoord = aTextureCoord;
}
</script>
<script type="text/javascript">
var gl;
function initGL(canvas) {
try {
gl = canvas.getContext("experimental-webgl");
gl.viewportWidth = canvas.width;
gl.viewportHeight = canvas.height;
} catch (e) {
}
if (!gl) {
alert("Could not initialise WebGL, sorry :-(");
}
}
function getShader(gl, id) {
var shaderScript = document.getElementById(id);
if (!shaderScript) {
return null;
}
var str = "";
var k = shaderScript.firstChild;
while (k) {
if (k.nodeType == 3) {
str += k.textContent;
}
k = k.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, str);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
var shaderProgram;
function initShaders() {
var fragmentShader = getShader(gl, "shader-fs");
var vertexShader = getShader(gl, "shader-vs");
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Could not initialise shaders");
}
gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
shaderProgram.textureCoordAttribute = gl.getAttribLocation(shaderProgram, "aTextureCoord");
gl.enableVertexAttribArray(shaderProgram.textureCoordAttribute);
shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
shaderProgram.samplerUniform = gl.getUniformLocation(shaderProgram, "uSampler");
shaderProgram.colorUniform = gl.getUniformLocation(shaderProgram, "uColor");
}
function handleLoadedTexture(texture) {
gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
gl.bindTexture(gl.TEXTURE_2D, texture);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, texture.image);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.bindTexture(gl.TEXTURE_2D, null);
}
var starTexture;
function initTexture() {
starTexture = gl.createTexture();
starTexture.image = new Image();
starTexture.image.onload = function () {
handleLoadedTexture(starTexture)
}
starTexture.image.src = "star.gif";
}
var mvMatrix = mat4.create();
var mvMatrixStack = [];
var pMatrix = mat4.create();
function mvPushMatrix() {
var copy = mat4.create();
mat4.set(mvMatrix, copy);
mvMatrixStack.push(copy);
}
function mvPopMatrix() {
if (mvMatrixStack.length == 0) {
throw "Invalid popMatrix!";
}
mvMatrix = mvMatrixStack.pop();
}
function setMatrixUniforms() {
gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}
function degToRad(degrees) {
return degrees * Math.PI / 180;
}
var currentlyPressedKeys = {};
function handleKeyDown(event) {
currentlyPressedKeys[event.keyCode] = true;
}
function handleKeyUp(event) {
currentlyPressedKeys[event.keyCode] = false;
}
var zoom = -15;
var tilt = 90;
var spin = 0;
function handleKeys() {
if (currentlyPressedKeys[33]) {
// Page Up
zoom -= 0.1;
}
if (currentlyPressedKeys[34]) {
// Page Down
zoom += 0.1;
}
if (currentlyPressedKeys[38]) {
// Up cursor key
tilt += 2;
}
if (currentlyPressedKeys[40]) {
// Down cursor key
tilt -= 2;
}
}
var starVertexPositionBuffer;
var starVertexTextureCoordBuffer;
function initBuffers() {
starVertexPositionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, starVertexPositionBuffer);
vertices = [
-1.0, -1.0, 0.0,
1.0, -1.0, 0.0,
-1.0, 1.0, 0.0,
1.0, 1.0, 0.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
starVertexPositionBuffer.itemSize = 3;
starVertexPositionBuffer.numItems = 4;
starVertexTextureCoordBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, starVertexTextureCoordBuffer);
var textureCoords = [
0.0, 0.0,
1.0, 0.0,
0.0, 1.0,
1.0, 1.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), gl.STATIC_DRAW);
starVertexTextureCoordBuffer.itemSize = 2;
starVertexTextureCoordBuffer.numItems = 4;
}
function drawStar() {
gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, starTexture);
gl.uniform1i(shaderProgram.samplerUniform, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, starVertexTextureCoordBuffer);
gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, starVertexTextureCoordBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, starVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, starVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
setMatrixUniforms();
gl.drawArrays(gl.TRIANGLE_STRIP, 0, starVertexPositionBuffer.numItems);
}
function Star(startingDistance, rotationSpeed) {
this.angle = 0;
this.dist = startingDistance;
this.rotationSpeed = rotationSpeed;
// Set the colors to a starting value.
this.randomiseColors();
}
Star.prototype.draw = function (tilt, spin, twinkle) {
mvPushMatrix();
// Move to the star's position
mat4.rotate(mvMatrix, degToRad(this.angle), [0.0, 1.0, 0.0]);
mat4.translate(mvMatrix, [this.dist, 0.0, 0.0]);
// Rotate back so that the star is facing the viewer
mat4.rotate(mvMatrix, degToRad(-this.angle), [0.0, 1.0, 0.0]);
mat4.rotate(mvMatrix, degToRad(-tilt), [1.0, 0.0, 0.0]);
if (twinkle) {
// Draw a non-rotating star in the alternate "twinkling" color
gl.uniform3f(shaderProgram.colorUniform, this.twinkleR, this.twinkleG, this.twinkleB);
drawStar();
}
// All stars spin around the Z axis at the same rate
mat4.rotate(mvMatrix, degToRad(spin), [0.0, 0.0, 1.0]);
// Draw the star in its main color
gl.uniform3f(shaderProgram.colorUniform, this.r, this.g, this.b);
drawStar()
mvPopMatrix();
};
var effectiveFPMS = 60 / 1000;
Star.prototype.animate = function (elapsedTime) {
this.angle += this.rotationSpeed * effectiveFPMS * elapsedTime;
// Decrease the distance, resetting the star to the outside of
// the spiral if it's at the center.
this.dist -= 0.01 * effectiveFPMS * elapsedTime;
if (this.dist < 0.0) {
this.dist += 5.0;
this.randomiseColors();
}
};
Star.prototype.randomiseColors = function () {
// Give the star a random color for normal
// circumstances...
this.r = Math.random();
this.g = Math.random();
this.b = Math.random();
// When the star is twinkling, we draw it twice, once
// in the color below (not spinning) and then once in the
// main color defined above.
this.twinkleR = Math.random();
this.twinkleG = Math.random();
this.twinkleB = Math.random();
};
var stars = [];
function initWorldObjects() {
var numStars = 50;
for (var i=0; i < numStars; i++) {
stars.push(new Star((i / numStars) * 5.0, i / numStars));
}
}
function drawScene() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
mat4.perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0, pMatrix);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE);
gl.enable(gl.BLEND);
mat4.identity(mvMatrix);
mat4.translate(mvMatrix, [0.0, 0.0, zoom]);
mat4.rotate(mvMatrix, degToRad(tilt), [1.0, 0.0, 0.0]);
var twinkle = document.getElementById("twinkle").checked;
for (var i in stars) {
stars[i].draw(tilt, spin, twinkle);
spin += 0.1;
}
}
var lastTime = 0;
function animate() {
var timeNow = new Date().getTime();
if (lastTime != 0) {
var elapsed = timeNow - lastTime;
for (var i in stars) {
stars[i].animate(elapsed);
}
}
lastTime = timeNow;
}
function tick() {
requestAnimFrame(tick);
handleKeys();
drawScene();
animate();
}
function webGLStart() {
var canvas = document.getElementById("lesson09-canvas");
initGL(canvas);
initShaders();
initBuffers();
initTexture();
initWorldObjects();
gl.clearColor(0.0, 0.0, 0.0, 1.0);
document.onkeydown = handleKeyDown;
document.onkeyup = handleKeyUp;
tick();
}
</script>
</head>
<body onload="webGLStart();">
<a href="http://learningwebgl.com/blog/?p=1008">&lt;&lt; Back to Lesson 9</a><br />
<canvas id="lesson09-canvas" style="border: none;" width="500" height="500"></canvas>
<br/>
<input type="checkbox" id="twinkle" /> Twinkle<br/>
(Use up/down cursor keys to rotate, and <code>Page Up</code>/<code>Page Down</code> to zoom out/in)
<br/>
<br/>
<a href="http://learningwebgl.com/blog/?p=1008">&lt;&lt; Back to Lesson 9</a>
</body>
</html>