We Keep Coding

Make a multiple objects with javascript and png

I'm trying to get a spaceship animation scene with a group of comets going down.
//Create a comet div with img attached to it
var cometScene = function(spaceNo){
var b = document.createElement('div');
b.id = 'cometio';
var cometImage = document.createElement('img');
cometImage.setAttribute('src', 'images/comet1.png');
b.appendChild(cometImage);
document.getElementById('wrap').appendChild(b);
}
//Comet move
function cometMove(){
var comet = document.getElementById('cometio');
var pos = 0;
var interval = setInterval(scene, 3);
function scene(){
if (pos === 1000){
clearInterval(interval);
} else {
pos++;
comet.style.top = pos + 'px';
comet.style.left = pos + 'px';
}
}
setInterval(scene, 3)
}
But when I call a function cometScene(3) I'm not getting 3 similar objects. Also how these objects can be allocated across the whole screen as this is just a single div.
function main(){
var w = document.createElement('div');
w.id = 'wrap';
document.querySelector('body').appendChild(w);
astronautScene();
cometScene();
shaceshipScene();
cometMove();
astronautMove();
}

This it what I would do:
Give the comets a class instead of an id, because there can be more of them.
Because there can be multiple use a loop to iterate through them
To give them the ability to move freely, they need to have position:absolute or something similiar
Don't use the same variable for the position of all comets, because they could be in different positions
To get the current position just parse the currect top and left value to a Number
//Create a comet div with img attached to it
var cometScene = function(spaceNo) {
var b = document.createElement('div');
b.className = 'cometio';
var cometImage = document.createElement('img');
cometImage.setAttribute('src', 'images/comet1.png');
b.appendChild(cometImage);
document.getElementById('wrap').appendChild(b);
}
//Comet move
function cometMove() {
var comets = document.getElementsByClassName('cometio');
for (let i = 0; i < comets.length; i++) {
const comet = comets[i];
comet.style.top = "0px";
comet.style.left = "0px";
comet.style.position = "absolute";
var interval = setInterval(scene, 3);
function scene() {
let x = parseInt(comet.style.left);
let y = parseInt(comet.style.top);
if (x === 1000) {
clearInterval(interval);
} else {
comet.style.top = (1 + x) + 'px';
comet.style.left = (1 + y) + 'px';
}
}
}
//setInterval(scene, 3)don't start the interval twice
}
function main() {
var w = document.createElement('div');
w.id = 'wrap';
document.querySelector('body').appendChild(w);
//astronautScene();
cometScene();
//shaceshipScene();
cometMove();
//astronautMove();
}
main();

Expand the width of an element with a setTimeOut loop

I am trying to create a simple javascript animation that will expand the width of an element from 0px to a specified width. Although this is probably a pretty elementary problem for some, I just can't seem to figure out what I am doing wrong. Instead of the loop running and expanding the div as desired I am only able to expand the div by repeatedly firing the function manually.
Fiddle
Current js code:
var el = document.getElementById('h');
var btn = document.getElementById('button1');
var oswidth = el.offsetWidth;
var target_width = 100;
btn.onclick = function grow() {
var loop = setTimeout('grow(\'' + el + '\')', 20);
if (oswidth < target_width) {
oswidth += 5;
} else {
clearTimeout(loop);
}
el.style.width = oswidth + 'px';
}
And as always, thank you in advance!

Try this code.fiddle-https://jsfiddle.net/L8kLx7d2/
var el = document.getElementById('h');
var btn = document.getElementById('button1');
var oswidth = el.offsetWidth;
var target_width = 100;
var loop;
function grow() {
if (oswidth < target_width) {
oswidth += 5;
} else {
clearInterval(loop);
}
el.style.width = oswidth + 'px';
}
btn.onclick=function(){
loop=setInterval(grow, 1000)};

Try this:
var el = document.getElementById('h');
var btn = document.getElementById('button1');
var oswidth = el.offsetWidth;
var target_width = 100;
btn.onclick = function grow() {
if (oswidth < target_width) {
oswidth += 5;
el.style.width = oswidth + 'px';
setTimeout(grow, 20);
}
}
I'll leave it to you to puzzle over the differences.

You can call the grow function in setInterval
JS:
var el = document.getElementById('h');
var btn = document.getElementById('button1');
var oswidth = el.offsetWidth;
var target_width = 100;
function grow() {
var loop = setTimeout('grow(\'' + el + '\')', 20);
if (oswidth < target_width) {
oswidth += 5;
} else {
clearTimeout(loop);
}
el.style.width = oswidth + 'px';
}
setInterval(grow, 1000);
Demo: http://jsfiddle.net/lotusgodkk/jeq834de/1/

There are three solutions. The first is using recursive setTimeout:
function grow(time) {
if (oswidth < target_width) {
oswidth += 5;
el.style.width = oswidth + 'px';
setTimeout(function() {grow(time);}, time);
}
}
The second is to use setInterval as described in the answer of K K.
The third is my personal favorite, using the transition css attribute.

Why does chrome struggle to display lots of images on a canvas when the other browsers don't?

We're working with the HTML5 canvas, displaying lots of images at one time.
This is working pretty well but recently we've had a problem with chrome.
When drawing images on to a canvas you seem to reach a certain point where the performance degrades very quickly.
It's not a slow effect, it seems that you go right from 60fps to 2-4fps.
Here's some reproduction code:
// Helpers
// https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Math/random
function getRandomInt(min, max) { return Math.floor(Math.random() * (max - min + 1)) + min; }
// http://www.paulirish.com/2011/requestanimationframe-for-smart-animating/
window.requestAnimFrame = (function () { return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) { window.setTimeout(callback, 1000 / 60); }; })();
// https://github.com/mrdoob/stats.js
var Stats = function () { var e = Date.now(), t = e; var n = 0, r = Infinity, i = 0; var s = 0, o = Infinity, u = 0; var a = 0, f = 0; var l = document.createElement("div"); l.id = "stats"; l.addEventListener("mousedown", function (e) { e.preventDefault(); y(++f % 2) }, false); l.style.cssText = "width:80px;opacity:0.9;cursor:pointer"; var c = document.createElement("div"); c.id = "fps"; c.style.cssText = "padding:0 0 3px 3px;text-align:left;background-color:#002"; l.appendChild(c); var h = document.createElement("div"); h.id = "fpsText"; h.style.cssText = "color:#0ff;font-family:Helvetica,Arial,sans-serif;font-size:9px;font-weight:bold;line-height:15px"; h.innerHTML = "FPS"; c.appendChild(h); var p = document.createElement("div"); p.id = "fpsGraph"; p.style.cssText = "position:relative;width:74px;height:30px;background-color:#0ff"; c.appendChild(p); while (p.children.length < 74) { var d = document.createElement("span"); d.style.cssText = "width:1px;height:30px;float:left;background-color:#113"; p.appendChild(d) } var v = document.createElement("div"); v.id = "ms"; v.style.cssText = "padding:0 0 3px 3px;text-align:left;background-color:#020;display:none"; l.appendChild(v); var m = document.createElement("div"); m.id = "msText"; m.style.cssText = "color:#0f0;font-family:Helvetica,Arial,sans-serif;font-size:9px;font-weight:bold;line-height:15px"; m.innerHTML = "MS"; v.appendChild(m); var g = document.createElement("div"); g.id = "msGraph"; g.style.cssText = "position:relative;width:74px;height:30px;background-color:#0f0"; v.appendChild(g); while (g.children.length < 74) { var d = document.createElement("span"); d.style.cssText = "width:1px;height:30px;float:left;background-color:#131"; g.appendChild(d) } var y = function (e) { f = e; switch (f) { case 0: c.style.display = "block"; v.style.display = "none"; break; case 1: c.style.display = "none"; v.style.display = "block"; break } }; var b = function (e, t) { var n = e.appendChild(e.firstChild); n.style.height = t + "px" }; return { REVISION: 11, domElement: l, setMode: y, begin: function () { e = Date.now() }, end: function () { var f = Date.now(); n = f - e; r = Math.min(r, n); i = Math.max(i, n); m.textContent = n + " MS (" + r + "-" + i + ")"; b(g, Math.min(30, 30 - n / 200 * 30)); a++; if (f > t + 1e3) { s = Math.round(a * 1e3 / (f - t)); o = Math.min(o, s); u = Math.max(u, s); h.textContent = s + " FPS (" + o + "-" + u + ")"; b(p, Math.min(30, 30 - s / 100 * 30)); t = f; a = 0 } return f }, update: function () { e = this.end() } } }
// Firefox events suck
function getOffsetXY(eventArgs) { return { X: eventArgs.offsetX == undefined ? eventArgs.layerX : eventArgs.offsetX, Y: eventArgs.offsetY == undefined ? eventArgs.layerY : eventArgs.offsetY }; }
function getWheelDelta(eventArgs) { if (!eventArgs) eventArgs = event; var w = eventArgs.wheelDelta; var d = eventArgs.detail; if (d) { if (w) { return w / d / 40 * d > 0 ? 1 : -1; } else { return -d / 3; } } else { return w / 120; } }
// Reproduction Code
var stats = new Stats();
document.body.appendChild(stats.domElement);
var masterCanvas = document.getElementById('canvas');
var masterContext = masterCanvas.getContext('2d');
var viewOffsetX = 0;
var viewOffsetY = 0;
var viewScaleFactor = 1;
var viewMinScaleFactor = 0.1;
var viewMaxScaleFactor = 10;
var mouseWheelSensitivity = 10; //Fudge Factor
var isMouseDown = false;
var lastMouseCoords = null;
var imageDimensionPixelCount = 25;
var paddingPixelCount = 2;
var canvasDimensionImageCount = 50;
var totalImageCount = Math.pow(canvasDimensionImageCount, 2);
var images = null;
function init() {
images = createLocalImages(totalImageCount, imageDimensionPixelCount);
initInteraction();
renderLoop();
}
function initInteraction() {
var handleMouseDown = function (eventArgs) {
isMouseDown = true;
var offsetXY = getOffsetXY(eventArgs);
lastMouseCoords = [
offsetXY.X,
offsetXY.Y
];
};
var handleMouseUp = function (eventArgs) {
isMouseDown = false;
lastMouseCoords = null;
}
var handleMouseMove = function (eventArgs) {
if (isMouseDown) {
var offsetXY = getOffsetXY(eventArgs);
var panX = offsetXY.X - lastMouseCoords[0];
var panY = offsetXY.Y - lastMouseCoords[1];
pan(panX, panY);
lastMouseCoords = [
offsetXY.X,
offsetXY.Y
];
}
};
var handleMouseWheel = function (eventArgs) {
var mouseX = eventArgs.pageX - masterCanvas.offsetLeft;
var mouseY = eventArgs.pageY - masterCanvas.offsetTop;
var zoom = 1 + (getWheelDelta(eventArgs) / mouseWheelSensitivity);
zoomAboutPoint(mouseX, mouseY, zoom);
if (eventArgs.preventDefault !== undefined) {
eventArgs.preventDefault();
} else {
return false;
}
}
masterCanvas.addEventListener("mousedown", handleMouseDown, false);
masterCanvas.addEventListener("mouseup", handleMouseUp, false);
masterCanvas.addEventListener("mousemove", handleMouseMove, false);
masterCanvas.addEventListener("mousewheel", handleMouseWheel, false);
masterCanvas.addEventListener("DOMMouseScroll", handleMouseWheel, false);
}
function pan(panX, panY) {
masterContext.translate(panX / viewScaleFactor, panY / viewScaleFactor);
viewOffsetX -= panX / viewScaleFactor;
viewOffsetY -= panY / viewScaleFactor;
}
function zoomAboutPoint(zoomX, zoomY, zoomFactor) {
var newCanvasScale = viewScaleFactor * zoomFactor;
if (newCanvasScale < viewMinScaleFactor) {
zoomFactor = viewMinScaleFactor / viewScaleFactor;
} else if (newCanvasScale > viewMaxScaleFactor) {
zoomFactor = viewMaxScaleFactor / viewScaleFactor;
}
masterContext.translate(viewOffsetX, viewOffsetY);
masterContext.scale(zoomFactor, zoomFactor);
viewOffsetX = ((zoomX / viewScaleFactor) + viewOffsetX) - (zoomX / (viewScaleFactor * zoomFactor));
viewOffsetY = ((zoomY / viewScaleFactor) + viewOffsetY) - (zoomY / (viewScaleFactor * zoomFactor));
viewScaleFactor *= zoomFactor;
masterContext.translate(-viewOffsetX, -viewOffsetY);
}
function renderLoop() {
clearCanvas();
renderCanvas();
stats.update();
requestAnimFrame(renderLoop);
}
function clearCanvas() {
masterContext.clearRect(viewOffsetX, viewOffsetY, masterCanvas.width / viewScaleFactor, masterCanvas.height / viewScaleFactor);
}
function renderCanvas() {
for (var imageY = 0; imageY < canvasDimensionImageCount; imageY++) {
for (var imageX = 0; imageX < canvasDimensionImageCount; imageX++) {
var x = imageX * (imageDimensionPixelCount + paddingPixelCount);
var y = imageY * (imageDimensionPixelCount + paddingPixelCount);
var imageIndex = (imageY * canvasDimensionImageCount) + imageX;
var image = images[imageIndex];
masterContext.drawImage(image, x, y, imageDimensionPixelCount, imageDimensionPixelCount);
}
}
}
function createLocalImages(imageCount, imageDimension) {
var tempCanvas = document.createElement('canvas');
tempCanvas.width = imageDimension;
tempCanvas.height = imageDimension;
var tempContext = tempCanvas.getContext('2d');
var images = new Array();
for (var imageIndex = 0; imageIndex < imageCount; imageIndex++) {
tempContext.clearRect(0, 0, imageDimension, imageDimension);
tempContext.fillStyle = "rgb(" + getRandomInt(0, 255) + ", " + getRandomInt(0, 255) + ", " + getRandomInt(0, 255) + ")";
tempContext.fillRect(0, 0, imageDimension, imageDimension);
var image = new Image();
image.src = tempCanvas.toDataURL('image/png');
images.push(image);
}
return images;
}
// Get this party started
init();
And a jsfiddle link for your interactive pleasure:
http://jsfiddle.net/BtyL6/14/
This is drawing 50px x 50px images in a 50 x 50 (2500) grid on the canvas. I've also quickly tried with 25px x 25px and 50 x 50 (2500) images.
We have other local examples that deal with bigger images and larger numbers of images and the other browser start to struggle with these at higher values.
As a quick test I jacked up the code in the js fiddle to 100px x 100px and 100 x 100 (10000) images and that was still running at 16fps when fully zoomed out. (Note: I had to lower the viewMinScaleFactor to 0.01 to fit it all in when zoomed out.)
Chrome on the other hand seems to hit some kind of limit and the FPS drops from 60 to 2-4.
Here's some info about what we've tried and the results:
We've tried using setinterval rather than requestAnimationFrame.
If you load 10 images and draw them 250 times each rather than 2500 images drawn once each then the problem goes away. This seems to indicate that chrome is hitting some kind of limit/trigger as to how much data it's storing about the rendering.
We have culling (not rendering images outside of the visual range) in our more complex examples and while this helps it's not a solution as we need to be able to show all the images at once.
We have the images only being rendered if there have been changes in our local code, against this helps (when nothing changes, obviously) but it isn't a full solution because the canvas should be interactive.
In the example code we're creating the images using a canvas, but the code can also be run hitting a web service to provide the images and the same behaviour (slowness) will be seen.
We've found it very hard to even search for this issue, most results are from a couple of years ago and woefully out of date.
If any more information would be useful then please ask!
EDIT: Changed js fiddle URL to reflect the same code as in the question. The code itself didn't actually change, just the formatting. But I want to be consistent.
EDIT: Updated jsfiddle and and code with css to prevent selection and call requestAnim after the render loop is done.

In Canary this code freezes it on my computer. As to why this happens in Chrome the simple answer is that it uses a different implementation than f.ex. FF. In-depth detail I don't know, but there is obviously room for optimizing the implementation in this area.
I can give some tip however on how you can optimize the given code to make it run in Chrome as well :-)
There are several things here:
You are storing each block of colors as images. This seem to have a huge performance impact on Canary / Chrome.
You are calling requestAnimationFrame at the beginning of the loop
You are clearing and rendering even if there are no changes
Try to (addressing the points):
If you only need solid blocks of colors, draw them directly using fillRect() instead and keep the color indexes in an array (instead of images). Even if you draw them to an off-screen canvas you will only have to do one draw to main canvas instead of multiple image draw operations.
Move requestAnimationFrame to the end of the code block to avoid stacking.
Use dirty flag to prevent unnecessary rendering:
I modified the code a bit - I modified it to use solid colors to demonstrate where the performance impact is in Chrome / Canary.
I set a dirty flag in global scope as true (to render the initial scene) which is set to true each time the mouse move occur:
//global
var isDirty = true;
//mouse move handler
var handleMouseMove = function (eventArgs) {
// other code
isDirty = true;
// other code
};
//render loop
function renderLoop() {
if (isDirty) {
clearCanvas();
renderCanvas();
}
stats.update();
requestAnimFrame(renderLoop);
}
//in renderCanvas at the end:
function renderCanvas() {
// other code
isDirty = false;
}
You will of course need to check for caveats for the isDirty flag elsewhere and also introduce more criteria if it's cleared at the wrong moment. I would store the old position of the mouse and only (in the mouse move) if it changed set the dirty flag - I didn't modify this part though.
As you can see you will be able to run this in Chrome and in FF at a higher FPS.
I also assume (I didn't test) that you can optimize the clearCanvas() function by only drawing the padding/gaps instead of clearing the whole canvas. But that need to be tested.
Added a CSS-rule to prevent the canvas to be selected when using the mouse:
For further optimizing in cases such as this, which is event driven, you don't actually need an animation loop at all. You can just call the redraw when the coords or mouse-wheel changes.
Modification:
http://jsfiddle.net/BtyL6/10/

This was a legitimate bug in chrome.
https://code.google.com/p/chromium/issues/detail?id=247912
It has now been fixed and should be in a chrome mainline release soon.

variable throwing 'undefined' error, cannot figure out

I'm using Raphael.js. Everytime i load the page i get an error that reads:
con is undefined
x = con.x
I looked up con in the Raphael documentation, and this is what i found:
var con = R._getContainer.apply(0, arguments),
container = con && con.container,
x = con.x,
y = con.y,
width = con.width,
height = con.height;
//...
con is clearly defined here. Here is the code I am trying to load:
var paper = new Raphael(ele('canvas_container'), 500, 500);
window.onload = function() {
var circle = paper.circle(100,100,100);
for (i = 0; i < 5; i++) {
var multiplier = i * 5;
paper.circle(250 + (2 * multiplier), 100 + multiplier, 50 - multiplier);
}
}
Has anyone else gotten this error? Is this a bug in the version of Raphael that I have or is there some other problem?

Try moving the paper instantiation inside your window's load function:
window.onload = function() {
var paper = new Raphael(ele('canvas_container'), 500, 500);
var circle = paper.circle(100,100,100);
for (i = 0; i < 5; i++) {
var multiplier = i * 5;
paper.circle(250 + (2 * multiplier), 100 + multiplier, 50 - multiplier);
}
}
If you try to get an element by its id before the DOM is ready, getElementById won't return anything. As you can see here, trying your code on an empty document shows the same result.

Raphael.js expects there to be a hard coded HTML element on the page with the name of the Raphael canvas (ie: "canvas_container"). If the HTML element is created during run time (dynamically in your JavaScript code), it will throw this error.
R._engine.create = function () {
var con = R._getContainer.apply(0, arguments),
container = con && con.container,
x = con.x,
y = con.y,
width = con.width,
height = con.height;
if (!container) {
throw new Error("SVG container not found.");
}
var cnvs = $("svg"),
css = "overflow:hidden;",
isFloating;
x = x || 0;
y = y || 0;
width = width || 512;
height = height || 342;
$(cnvs, {
height: height,
version: 1.1,
width: width,
xmlns: "http://www.w3.org/2000/svg"
});
if (container == 1) {
cnvs.style.cssText = css + "position:absolute;left:" + x + "px;top:" + y + "px";
R._g.doc.body.appendChild(cnvs);
isFloating = 1;
} else {
cnvs.style.cssText = css + "position:relative";
if (container.firstChild) {
container.insertBefore(cnvs, container.firstChild);
} else {
container.appendChild(cnvs);
}
}
container = new R._Paper;
container.width = width;
container.height = height;
container.canvas = cnvs;
container.clear();
container._left = container._top = 0;
isFloating && (container.renderfix = function () {});
container.renderfix();
return container;
};

Javascript News Scroller

see the news scroller on the top of this site
http://track.dc.gov/Agency/DH0
Any idea what library/functions this site uses to implment such a smooth scroller?

They have a very nicely formatted block of code you can study. Open your favorite JS debugger when you visit the site, wait for everything to get moving, and then press "Break All" or the equivalent in your debugger. You'll see something like the following:
Dashboard.UI.EndlessLine = function() {
var me = this;
me.jq = $(me);
me.classNames = { CONTAINER: "uiEndless", VIEW: "uiEndlessView", CANVAS: "uiEndlessCanvas", TILE: "uiEndlessTile" };
var canvas = null;
var view = null;
var tiles = null;
var x = 0;
var xx = 0;
var canvasWidth = 0;
var step = 1;
var delay = 40;
me.initialize = function(container, data, handler) {
required(container, "container");
required(data, "data");
required(handler, "handler");
container.addClass(me.classNames.CONTAINER);
view = newDiv(me.classNames.VIEW);
canvas = newDiv(me.classNames.CANVAS);
view.append(canvas);
container.append(view);
x = 0;
xx = 0;
canvasWidth = 0;
tiles = me.populateTiles(data, handler);
container.click(function() {
if (me.started()) me.stop(); else me.start();
});
};
me._resize = function(size) {
};
var moveId = 0;
me.start = function() {
me.stop();
me.tick();
}
me.stop = function() {
if (moveId > 0) clearTimeout(moveId);
moveId = 0;
}
me.started = function() {
return moveId > 0;
};
me.tick = function() {
var tile = tiles.current();
var width = tile.calculatedWidth;
if (x < width - step) {
x += step;
} else {
x = 0;
tile.css("left", canvasWidth + "px");
if (tiles.advance()) {
xx = 0;
canvasWidth = 0;
do {
current = tiles.current();
width = current.calculatedWidth;
current[0].style.left = canvasWidth + "px";
canvasWidth += width;
} while (!tiles.advance());
} else {
canvasWidth += width;
}
}
canvas[0].style.left = -(xx) + "px";
xx += step;
moveId = setTimeout(me.tick, delay);
}
me.populateTiles = function(data, handler) {
var tiles = new Dashboard.Core.List();
var viewWidth = view.contentWidth();
var maxHeight = 0;
each(data, function() {
var tile = newDiv(me.classNames.TILE);
handler.call(this, tile);
tile.css({ left: canvasWidth + "px", top: 0 });
canvas.append(tile);
var width = tile.outerWidth();
var height = tile.outerHeight();
if (maxHeight < height) maxHeight = height;
tile.calculatedWidth = width;
canvasWidth += width; // getting width may only be done after the element is attached to DOM
tiles.append(tile);
view.height(height);
});
return tiles.createCycle();
}
}
I'm impressed -- everything looks professional and nicely namespaced.
Update: If you want an explanation of how it works, focus on the tick method defined above. Glossing over all the details (cause I haven't really studied it myself), it calculates a step size, moves the message element to the left by the some amount, and schedules the next tick call for 40 milliseconds in the future.

jQuery enthusiast, Remy Sharp, has his own Marquee Plugin that you can implement pretty easily. You can gather deeper details of it on his blog or by visiting the demo page.
For Mootools users, there's Mooquee.
You can also view the actual code for this example online at http://track.dc.gov/Resource/Script/ - do a search for "uiEndless" to find the target-scripting.