Bouncing Balls
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Copyright 2006 Google Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
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See the License for the specific language governing permissions and
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<html>
<head>
<title>ExplorerCanvas Example 1</title>
<script type="text/javascript">
/*
ExplorerCanvas
Copyright 2006 Google Inc.
-------------------------------------------------------------------------------
DESCRIPTION
Firefox, Safari and Opera 9 support the canvas tag to allow 2D command-based
drawing operations. ExplorerCanvas brings the same functionality to Internet
Explorer; web developers only need to include a single script tag in their
existing canvas webpages to enable this support.
If you run into trouble, please look at the included example code to see how
to best implement this
ExplorerCanvas
Google Open Source:
<http://code.google.com>
<opensource@google.com>
Developers:
Emil A Eklund <emil@eae.net>
Erik Arvidsson <erik@eae.net>
Glen Murphy <glen@glenmurphy.com>
*/
// Copyright 2006 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Known Issues:
//
// * Patterns are not implemented.
// * Radial gradient are not implemented. The VML version of these look very
// different from the canvas one.
// * Clipping paths are not implemented.
// * Coordsize. The width and height attribute have higher priority than the
// width and height style values which isn't correct.
// * Painting mode isn't implemented.
// * Canvas width/height should is using content-box by default. IE in
// Quirks mode will draw the canvas using border-box. Either change your
// doctype to HTML5
// (http://www.whatwg.org/specs/web-apps/current-work/#the-doctype)
// or use Box Sizing Behavior from WebFX
// (http://webfx.eae.net/dhtml/boxsizing/boxsizing.html)
// * Optimize. There is always room for speed improvements.
// only add this code if we do not already have a canvas implementation
if (!window.CanvasRenderingContext2D) {
(function () {
// alias some functions to make (compiled) code shorter
var m = Math;
var mr = m.round;
var ms = m.sin;
var mc = m.cos;
// this is used for sub pixel precision
var Z = 10;
var Z2 = Z / 2;
var G_vmlCanvasManager_ = {
init: function (opt_doc) {
var doc = opt_doc || document;
if (/MSIE/.test(navigator.userAgent) && !window.opera) {
var self = this;
doc.attachEvent("onreadystatechange", function () {
self.init_(doc);
});
}
},
init_: function (doc) {
if (doc.readyState == "complete") {
// create xmlns
if (!doc.namespaces["g_vml_"]) {
doc.namespaces.add("g_vml_", "urn:schemas-microsoft-com:vml");
}
// setup default css
var ss = doc.createStyleSheet();
ss.cssText = "canvas{display:inline-block;overflow:hidden;" +
// default size is 300x150 in Gecko and Opera
"text-align:left;width:300px;height:150px}" +
"g_vml_\\:*{behavior:url(#default#VML)}";
// find all canvas elements
var els = doc.getElementsByTagName("canvas");
for (var i = 0; i < els.length; i++) {
if (!els[i].getContext) {
this.initElement(els[i]);
}
}
}
},
fixElement_: function (el) {
// in IE before version 5.5 we would need to add HTML: to the tag name
// but we do not care about IE before version 6
var outerHTML = el.outerHTML;
var newEl = el.ownerDocument.createElement(outerHTML);
// if the tag is still open IE has created the children as siblings and
// it has also created a tag with the name "/FOO"
if (outerHTML.slice(-2) != "/>") {
var tagName = "/" + el.tagName;
var ns;
// remove content
while ((ns = el.nextSibling) && ns.tagName != tagName) {
ns.removeNode();
}
// remove the incorrect closing tag
if (ns) {
ns.removeNode();
}
}
el.parentNode.replaceChild(newEl, el);
return newEl;
},
/**
* Public initializes a canvas element so that it can be used as canvas
* element from now on. This is called automatically before the page is
* loaded but if you are creating elements using createElement you need to
* make sure this is called on the element.
* @param {HTMLElement} el The canvas element to initialize.
* @return {HTMLElement} the element that was created.
*/
initElement: function (el) {
el = this.fixElement_(el);
el.getContext = function () {
if (this.context_) {
return this.context_;
}
return this.context_ = new CanvasRenderingContext2D_(this);
};
// do not use inline function because that will leak memory
el.attachEvent('onpropertychange', onPropertyChange);
el.attachEvent('onresize', onResize);
var attrs = el.attributes;
if (attrs.width && attrs.width.specified) {
// TODO: use runtimeStyle and coordsize
// el.getContext().setWidth_(attrs.width.nodeValue);
el.style.width = attrs.width.nodeValue + "px";
} else {
el.width = el.clientWidth;
}
if (attrs.height && attrs.height.specified) {
// TODO: use runtimeStyle and coordsize
// el.getContext().setHeight_(attrs.height.nodeValue);
el.style.height = attrs.height.nodeValue + "px";
} else {
el.height = el.clientHeight;
}
//el.getContext().setCoordsize_()
return el;
}
};
function onPropertyChange(e) {
var el = e.srcElement;
switch (e.propertyName) {
case 'width':
el.style.width = el.attributes.width.nodeValue + "px";
el.getContext().clearRect();
break;
case 'height':
el.style.height = el.attributes.height.nodeValue + "px";
el.getContext().clearRect();
break;
}
}
function onResize(e) {
var el = e.srcElement;
if (el.firstChild) {
el.firstChild.style.width = el.clientWidth + 'px';
el.firstChild.style.height = el.clientHeight + 'px';
}
}
G_vmlCanvasManager_.init();
// precompute "00" to "FF"
var dec2hex = [];
for (var i = 0; i < 16; i++) {
for (var j = 0; j < 16; j++) {
dec2hex[i * 16 + j] = i.toString(16) + j.toString(16);
}
}
function createMatrixIdentity() {
return [
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]
];
}
function matrixMultiply(m1, m2) {
var result = createMatrixIdentity();
for (var x = 0; x < 3; x++) {
for (var y = 0; y < 3; y++) {
var sum = 0;
for (var z = 0; z < 3; z++) {
sum += m1[x][z] * m2[z][y];
}
result[x][y] = sum;
}
}
return result;
}
function copyState(o1, o2) {
o2.fillStyle = o1.fillStyle;
o2.lineCap = o1.lineCap;
o2.lineJoin = o1.lineJoin;
o2.lineWidth = o1.lineWidth;
o2.miterLimit = o1.miterLimit;
o2.shadowBlur = o1.shadowBlur;
o2.shadowColor = o1.shadowColor;
o2.shadowOffsetX = o1.shadowOffsetX;
o2.shadowOffsetY = o1.shadowOffsetY;
o2.strokeStyle = o1.strokeStyle;
o2.arcScaleX_ = o1.arcScaleX_;
o2.arcScaleY_ = o1.arcScaleY_;
}
function processStyle(styleString) {
var str, alpha = 1;
styleString = String(styleString);
if (styleString.substring(0, 3) == "rgb") {
var start = styleString.indexOf("(", 3);
var end = styleString.indexOf(")", start + 1);
var guts = styleString.substring(start + 1, end).split(",");
str = "#";
for (var i = 0; i < 3; i++) {
str += dec2hex[Number(guts[i])];
}
if ((guts.length == 4) && (styleString.substr(3, 1) == "a")) {
alpha = guts[3];
}
} else {
str = styleString;
}
return [str, alpha];
}
function processLineCap(lineCap) {
switch (lineCap) {
case "butt":
return "flat";
case "round":
return "round";
case "square":
default:
return "square";
}
}
/**
* This class implements CanvasRenderingContext2D interface as described by
* the WHATWG.
* @param {HTMLElement} surfaceElement The element that the 2D context should
* be associated with
*/
function CanvasRenderingContext2D_(surfaceElement) {
this.m_ = createMatrixIdentity();
this.mStack_ = [];
this.aStack_ = [];
this.currentPath_ = [];
// Canvas context properties
this.strokeStyle = "#000";
this.fillStyle = "#000";
this.lineWidth = 1;
this.lineJoin = "miter";
this.lineCap = "butt";
this.miterLimit = Z * 1;
this.globalAlpha = 1;
this.canvas = surfaceElement;
var el = surfaceElement.ownerDocument.createElement('div');
el.style.width = surfaceElement.clientWidth + 'px';
el.style.height = surfaceElement.clientHeight + 'px';
el.style.overflow = 'hidden';
el.style.position = 'absolute';
surfaceElement.appendChild(el);
this.element_ = el;
this.arcScaleX_ = 1;
this.arcScaleY_ = 1;
};
var contextPrototype = CanvasRenderingContext2D_.prototype;
contextPrototype.clearRect = function() {
this.element_.innerHTML = "";
this.currentPath_ = [];
};
contextPrototype.beginPath = function() {
// TODO: Branch current matrix so that save/restore has no effect
// as per safari docs.
this.currentPath_ = [];
};
contextPrototype.moveTo = function(aX, aY) {
this.currentPath_.push({type: "moveTo", x: aX, y: aY});
this.currentX_ = aX;
this.currentY_ = aY;
};
contextPrototype.lineTo = function(aX, aY) {
this.currentPath_.push({type: "lineTo", x: aX, y: aY});
this.currentX_ = aX;
this.currentY_ = aY;
};
contextPrototype.bezierCurveTo = function(aCP1x, aCP1y,
aCP2x, aCP2y,
aX, aY) {
this.currentPath_.push({type: "bezierCurveTo",
cp1x: aCP1x,
cp1y: aCP1y,
cp2x: aCP2x,
cp2y: aCP2y,
x: aX,
y: aY});
this.currentX_ = aX;
this.currentY_ = aY;
};
contextPrototype.quadraticCurveTo = function(aCPx, aCPy, aX, aY) {
// the following is lifted almost directly from
// http://developer.mozilla.org/en/docs/Canvas_tutorial:Drawing_shapes
var cp1x = this.currentX_ + 2.0 / 3.0 * (aCPx - this.currentX_);
var cp1y = this.currentY_ + 2.0 / 3.0 * (aCPy - this.currentY_);
var cp2x = cp1x + (aX - this.currentX_) / 3.0;
var cp2y = cp1y + (aY - this.currentY_) / 3.0;
this.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, aX, aY);
};
contextPrototype.arc = function(aX, aY, aRadius,
aStartAngle, aEndAngle, aClockwise) {
aRadius *= Z;
var arcType = aClockwise ? "at" : "wa";
var xStart = aX + (mc(aStartAngle) * aRadius) - Z2;
var yStart = aY + (ms(aStartAngle) * aRadius) - Z2;
var xEnd = aX + (mc(aEndAngle) * aRadius) - Z2;
var yEnd = aY + (ms(aEndAngle) * aRadius) - Z2;
// IE won't render arches drawn counter clockwise if xStart == xEnd.
if (xStart == xEnd && !aClockwise) {
xStart += 0.125; // Offset xStart by 1/80 of a pixel. Use something
// that can be represented in binary
}
this.currentPath_.push({type: arcType,
x: aX,
y: aY,
radius: aRadius,
xStart: xStart,
yStart: yStart,
xEnd: xEnd,
yEnd: yEnd});
};
contextPrototype.rect = function(aX, aY, aWidth, aHeight) {
this.moveTo(aX, aY);
this.lineTo(aX + aWidth, aY);
this.lineTo(aX + aWidth, aY + aHeight);
this.lineTo(aX, aY + aHeight);
this.closePath();
};
contextPrototype.strokeRect = function(aX, aY, aWidth, aHeight) {
// Will destroy any existing path (same as FF behaviour)
this.beginPath();
this.moveTo(aX, aY);
this.lineTo(aX + aWidth, aY);
this.lineTo(aX + aWidth, aY + aHeight);
this.lineTo(aX, aY + aHeight);
this.closePath();
this.stroke();
};
contextPrototype.fillRect = function(aX, aY, aWidth, aHeight) {
// Will destroy any existing path (same as FF behaviour)
this.beginPath();
this.moveTo(aX, aY);
this.lineTo(aX + aWidth, aY);
this.lineTo(aX + aWidth, aY + aHeight);
this.lineTo(aX, aY + aHeight);
this.closePath();
this.fill();
};
contextPrototype.createLinearGradient = function(aX0, aY0, aX1, aY1) {
var gradient = new CanvasGradient_("gradient");
return gradient;
};
contextPrototype.createRadialGradient = function(aX0, aY0,
aR0, aX1,
aY1, aR1) {
var gradient = new CanvasGradient_("gradientradial");
gradient.radius1_ = aR0;
gradient.radius2_ = aR1;
gradient.focus_.x = aX0;
gradient.focus_.y = aY0;
return gradient;
};
contextPrototype.drawImage = function (image, var_args) {
var dx, dy, dw, dh, sx, sy, sw, sh;
// to find the original width we overide the width and height
var oldRuntimeWidth = image.runtimeStyle.width;
var oldRuntimeHeight = image.runtimeStyle.height;
image.runtimeStyle.width = 'auto';
image.runtimeStyle.height = 'auto';
// get the original size
var w = image.width;
var h = image.height;
// and remove overides
image.runtimeStyle.width = oldRuntimeWidth;
image.runtimeStyle.height = oldRuntimeHeight;
if (arguments.length == 3) {
dx = arguments[1];
dy = arguments[2];
sx = sy = 0;
sw = dw = w;
sh = dh = h;
} else if (arguments.length == 5) {
dx = arguments[1];
dy = arguments[2];
dw = arguments[3];
dh = arguments[4];
sx = sy = 0;
sw = w;
sh = h;
} else if (arguments.length == 9) {
sx = arguments[1];
sy = arguments[2];
sw = arguments[3];
sh = arguments[4];
dx = arguments[5];
dy = arguments[6];
dw = arguments[7];
dh = arguments[8];
} else {
throw "Invalid number of arguments";
}
var d = this.getCoords_(dx, dy);
var w2 = sw / 2;
var h2 = sh / 2;
var vmlStr = [];
var W = 10;
var H = 10;
// For some reason that I've now forgotten, using divs didn't work
vmlStr.push(' <g_vml_:group',
' coordsize="', Z * W, ',', Z * H, '"',
' coordorigin="0,0"' ,
' style="width:', W, ';height:', H, ';position:absolute;');
// If filters are necessary (rotation exists), create them
// filters are bog-slow, so only create them if abbsolutely necessary
// The following check doesn't account for skews (which don't exist
// in the canvas spec (yet) anyway.
if (this.m_[0][0] != 1 || this.m_[0][1]) {
var filter = [];
// Note the 12/21 reversal
filter.push("M11='", this.m_[0][0], "',",
"M12='", this.m_[1][0], "',",
"M21='", this.m_[0][1], "',",
"M22='", this.m_[1][1], "',",
"Dx='", mr(d.x / Z), "',",
"Dy='", mr(d.y / Z), "'");
// Bounding box calculation (need to minimize displayed area so that
// filters don't waste time on unused pixels.
var max = d;
var c2 = this.getCoords_(dx + dw, dy);
var c3 = this.getCoords_(dx, dy + dh);
var c4 = this.getCoords_(dx + dw, dy + dh);
max.x = Math.max(max.x, c2.x, c3.x, c4.x);
max.y = Math.max(max.y, c2.y, c3.y, c4.y);
vmlStr.push("padding:0 ", mr(max.x / Z), "px ", mr(max.y / Z),
"px 0;filter:progid:DXImageTransform.Microsoft.Matrix(",
filter.join(""), ", sizingmethod='clip');")
} else {
vmlStr.push("top:", mr(d.y / Z), "px;left:", mr(d.x / Z), "px;")
}
vmlStr.push(' ">' ,
'<g_vml_:image src="', image.src, '"',
' style="width:', Z * dw, ';',
' height:', Z * dh, ';"',
' cropleft="', sx / w, '"',
' croptop="', sy / h, '"',
' cropright="', (w - sx - sw) / w, '"',
' cropbottom="', (h - sy - sh) / h, '"',
' />',
'</g_vml_:group>');
this.element_.insertAdjacentHTML("BeforeEnd",
vmlStr.join(""));
};
contextPrototype.stroke = function(aFill) {
var lineStr = [];
var lineOpen = false;
var a = processStyle(aFill ? this.fillStyle : this.strokeStyle);
var color = a[0];
var opacity = a[1] * this.globalAlpha;
var W = 10;
var H = 10;
lineStr.push('<g_vml_:shape',
' fillcolor="', color, '"',
' filled="', Boolean(aFill), '"',
' style="position:absolute;width:', W, ';height:', H, ';"',
' coordorigin="0 0" coordsize="', Z * W, ' ', Z * H, '"',
' stroked="', !aFill, '"',
' strokeweight="', this.lineWidth, '"',
' strokecolor="', color, '"',
' path="');
var newSeq = false;
var min = {x: null, y: null};
var max = {x: null, y: null};
for (var i = 0; i < this.currentPath_.length; i++) {
var p = this.currentPath_[i];
if (p.type == "moveTo") {
lineStr.push(" m ");
var c = this.getCoords_(p.x, p.y);
lineStr.push(mr(c.x), ",", mr(c.y));
} else if (p.type == "lineTo") {
lineStr.push(" l ");
var c = this.getCoords_(p.x, p.y);
lineStr.push(mr(c.x), ",", mr(c.y));
} else if (p.type == "close") {
lineStr.push(" x ");
} else if (p.type == "bezierCurveTo") {
lineStr.push(" c ");
var c = this.getCoords_(p.x, p.y);
var c1 = this.getCoords_(p.cp1x, p.cp1y);
var c2 = this.getCoords_(p.cp2x, p.cp2y);
lineStr.push(mr(c1.x), ",", mr(c1.y), ",",
mr(c2.x), ",", mr(c2.y), ",",
mr(c.x), ",", mr(c.y));
} else if (p.type == "at" || p.type == "wa") {
lineStr.push(" ", p.type, " ");
var c = this.getCoords_(p.x, p.y);
var cStart = this.getCoords_(p.xStart, p.yStart);
var cEnd = this.getCoords_(p.xEnd, p.yEnd);
lineStr.push(mr(c.x - this.arcScaleX_ * p.radius), ",",
mr(c.y - this.arcScaleY_ * p.radius), " ",
mr(c.x + this.arcScaleX_ * p.radius), ",",
mr(c.y + this.arcScaleY_ * p.radius), " ",
mr(cStart.x), ",", mr(cStart.y), " ",
mr(cEnd.x), ",", mr(cEnd.y));
}
// TODO: Following is broken for curves due to
// move to proper paths.
// Figure out dimensions so we can do gradient fills
// properly
if(c) {
if (min.x == null || c.x < min.x) {
min.x = c.x;
}
if (max.x == null || c.x > max.x) {
max.x = c.x;
}
if (min.y == null || c.y < min.y) {
min.y = c.y;
}
if (max.y == null || c.y > max.y) {
max.y = c.y;
}
}
}
lineStr.push(' ">');
if (typeof this.fillStyle == "object") {
var focus = {x: "50%", y: "50%"};
var width = (max.x - min.x);
var height = (max.y - min.y);
var dimension = (width > height) ? width : height;
focus.x = mr((this.fillStyle.focus_.x / width) * 100 + 50) + "%";
focus.y = mr((this.fillStyle.focus_.y / height) * 100 + 50) + "%";
var colors = [];
// inside radius (%)
if (this.fillStyle.type_ == "gradientradial") {
var inside = (this.fillStyle.radius1_ / dimension * 100);
// percentage that outside radius exceeds inside radius
var expansion = (this.fillStyle.radius2_ / dimension * 100) - inside;
} else {
var inside = 0;
var expansion = 100;
}
var insidecolor = {offset: null, color: null};
var outsidecolor = {offset: null, color: null};
// We need to sort 'colors' by percentage, from 0 > 100 otherwise ie
// won't interpret it correctly
this.fillStyle.colors_.sort(function (cs1, cs2) {
return cs1.offset - cs2.offset;
});
for (var i = 0; i < this.fillStyle.colors_.length; i++) {
var fs = this.fillStyle.colors_[i];
colors.push( (fs.offset * expansion) + inside, "% ", fs.color, ",");
if (fs.offset > insidecolor.offset || insidecolor.offset == null) {
insidecolor.offset = fs.offset;
insidecolor.color = fs.color;
}
if (fs.offset < outsidecolor.offset || outsidecolor.offset == null) {
outsidecolor.offset = fs.offset;
outsidecolor.color = fs.color;
}
}
colors.pop();
lineStr.push('<g_vml_:fill',
' color="', outsidecolor.color, '"',
' color2="', insidecolor.color, '"',
' type="', this.fillStyle.type_, '"',
' focusposition="', focus.x, ', ', focus.y, '"',
' colors="', colors.join(""), '"',
' opacity="', opacity, '" />');
} else if (aFill) {
lineStr.push('<g_vml_:fill color="', color, '" opacity="', opacity, '" />');
} else {
lineStr.push(
'<g_vml_:stroke',
' opacity="', opacity,'"',
' joinstyle="', this.lineJoin, '"',
' miterlimit="', this.miterLimit, '"',
' endcap="', processLineCap(this.lineCap) ,'"',
' weight="', this.lineWidth, 'px"',
' color="', color,'" />'
);
}
lineStr.push("</g_vml_:shape>");
this.element_.insertAdjacentHTML("beforeEnd", lineStr.join(""));
this.currentPath_ = [];
};
contextPrototype.fill = function() {
this.stroke(true);
}
contextPrototype.closePath = function() {
this.currentPath_.push({type: "close"});
};
/**
* @private
*/
contextPrototype.getCoords_ = function(aX, aY) {
return {
x: Z * (aX * this.m_[0][0] + aY * this.m_[1][0] + this.m_[2][0]) - Z2,
y: Z * (aX * this.m_[0][1] + aY * this.m_[1][1] + this.m_[2][1]) - Z2
}
};
contextPrototype.save = function() {
var o = {};
copyState(this, o);
this.aStack_.push(o);
this.mStack_.push(this.m_);
this.m_ = matrixMultiply(createMatrixIdentity(), this.m_);
};
contextPrototype.restore = function() {
copyState(this.aStack_.pop(), this);
this.m_ = this.mStack_.pop();
};
contextPrototype.translate = function(aX, aY) {
var m1 = [
[1, 0, 0],
[0, 1, 0],
[aX, aY, 1]
];
this.m_ = matrixMultiply(m1, this.m_);
};
contextPrototype.rotate = function(aRot) {
var c = mc(aRot);
var s = ms(aRot);
var m1 = [
[c, s, 0],
[-s, c, 0],
[0, 0, 1]
];
this.m_ = matrixMultiply(m1, this.m_);
};
contextPrototype.scale = function(aX, aY) {
this.arcScaleX_ *= aX;
this.arcScaleY_ *= aY;
var m1 = [
[aX, 0, 0],
[0, aY, 0],
[0, 0, 1]
];
this.m_ = matrixMultiply(m1, this.m_);
};
/******** STUBS ********/
contextPrototype.clip = function() {
// TODO: Implement
};
contextPrototype.arcTo = function() {
// TODO: Implement
};
contextPrototype.createPattern = function() {
return new CanvasPattern_;
};
// Gradient / Pattern Stubs
function CanvasGradient_(aType) {
this.type_ = aType;
this.radius1_ = 0;
this.radius2_ = 0;
this.colors_ = [];
this.focus_ = {x: 0, y: 0};
}
CanvasGradient_.prototype.addColorStop = function(aOffset, aColor) {
aColor = processStyle(aColor);
this.colors_.push({offset: 1-aOffset, color: aColor});
};
function CanvasPattern_() {}
// set up externs
G_vmlCanvasManager = G_vmlCanvasManager_;
CanvasRenderingContext2D = CanvasRenderingContext2D_;
CanvasGradient = CanvasGradient_;
CanvasPattern = CanvasPattern_;
})();
} // if
</script>
<script type="text/javascript">
var canvas, ctx;
var particles = [];
var NUM_PARTICLES = 20;
function Particle() {
this.x = Math.random() * canvas.width;
this.y = Math.random() * canvas.height;
this.xvel = Math.random() * 5 - 2.5;
this.yvel = Math.random() * 5 - 2.5;
}
Particle.prototype.update = function() {
this.x += this.xvel;
this.y += this.yvel;
this.yvel += 0.1;
if (this.x > canvas.width || this.x < 0) {
this.xvel = -this.xvel;
}
if (this.y > canvas.height || this.y < 0) {
this.yvel = -this.yvel;
}
}
function loop() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
for(var i = 0; i < NUM_PARTICLES; i++) {
particles[i].update();
ctx.beginPath();
ctx.moveTo(particles[i].x, particles[i].y);
ctx.lineTo(particles[i].x - particles[i].xvel,
particles[i].y - particles[i].yvel);
ctx.stroke();
ctx.closePath();
}
setTimeout(loop, 10);
}
function load() {
canvas = document.getElementById("cv");
ctx = canvas.getContext("2d");
for(var i = 0; i < NUM_PARTICLES; i++) {
particles[i] = new Particle();
}
ctx.lineWidth = "2";
ctx.strokeStyle = "rgb(255, 255, 255)";
loop();
}
</script>
<style>
body {
background-color:black;
margin:50px;
text-align:center;
}
canvas {
border:1px solid #444;
}
</style>
</head>
<body onload="load();">
<canvas id="cv" width="400" height="300"></canvas>
</body>
</html>
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