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.
Related
I'm trying to get a nice knob/dial that can be rotated to send a value back to the server via websockets.
The basic premise works well, I got the code from the web.
I am trying to modify the code so that I get a prettier knob. I've been successful by placing the canvas inside a couple of divs which display static images, while the canvas rotates a translucent image in response to mouse/touch events.
The additions that I made to the code work well on the desktop (I'm running Firefox 45.0.2) but do not work at all on an iPad (Safari, iOS 9.3.5) and only partially on an iPhone (iOS 10.2.1)
On the iPhone, the knob rotates in the opposite direction to that expected, and often only horizontal movement will start the knob rotating.
I'm not using (nor do I want to use) any libraries such as jquery.
The code below will work as is. However, removing the comment marks in the body section will cause the problems I indicated.
(Oh and to forestall any comments, the black background and odd text colour is just there to so that you can see the translucent element without the static backgrounds)
I'm not at all experienced with jscript and can only just manage to follow what the code is doing at the moment. (one of the reasons I don't want to use additional libraries)
I suspect that the problem lies with how the touch event coordinates are interpreted, but I can't test them in any way.
Any help or suggestions would be appreciated.
HTML Code:
<!DOCTYPE html>
<html>
<head>
<title>Stepper example</title>
<meta name="viewport" content="width=device-width, initial-scale=0.7">
<style>
body {
text-align: center; background-color: black;
color: red
}
.container{
position: relative;
background: url(step_background.png);
width: 480px;
height: 480px;
margin: auto;
z-index:1;
}
.knob{
position: relative;
top: 59px;
background: url(knob_bg.png);
width: 362px;
height:362px;
margin:auto;
z-index:2;
}
#stepper{
position: relative;
}
</style>
<script>
var MIN_TOUCH_RADIUS = 20;
var MAX_TOUCH_RADIUS = 200;
var CANVAS_WIDTH = 362, CANVAS_HEIGHT = 362;
var PIVOT_X = 181, PIVOT_Y = 181;
var plate_angle = 0;
var plate_img = new Image();
var click_state = 0;
var last_angle_pos = 0;
var mouse_xyra = {x:0, y:0, r:0.0, a:0.0};
var ws;
plate_img.src = "knob_fg.png";
function init() {
var stepper = document.getElementById("stepper");
var ctx = stepper.getContext("2d");
stepper.width = CANVAS_WIDTH;
stepper.height = CANVAS_HEIGHT;
stepper.addEventListener("touchstart", mouse_down);
stepper.addEventListener("touchend", mouse_up);
stepper.addEventListener("touchmove", mouse_move);
stepper.addEventListener("mousedown", mouse_down);
stepper.addEventListener("mouseup", mouse_up);
stepper.addEventListener("mousemove", mouse_move);
ctx.translate(PIVOT_X, PIVOT_Y);
rotate_plate(plate_angle);
}
function connect_onclick() {
if(ws == null) {
ws = new WebSocket('ws://'+ window.location.hostname + ':81/', ['arduino']);
document.getElementById("ws_state").innerHTML = "CONNECTING";
ws.onopen = ws_onopen;
ws.onclose = ws_onclose;
ws.onmessage = ws_onmessage;
ws.onerror = function(){ alert("websocket error " + this.url) };
}
else
ws.close();
}
function ws_onopen() {
document.getElementById("ws_state").innerHTML = "<font color='blue'>CONNECTED</font>";
document.getElementById("bt_connect").innerHTML = "Disconnect";
rotate_plate(plate_angle);
}
function ws_onclose() {
document.getElementById("ws_state").innerHTML = "<font color='gray'>CLOSED</font>";
document.getElementById("bt_connect").innerHTML = "Connect";
ws.onopen = null;
ws.onclose = null;
ws.onmessage = null;
ws = null;
rotate_plate(plate_angle);
}
function ws_onmessage(e_msg) {
e_msg = e_msg || window.event; // MessageEvent
plate_angle = Number(e_msg.data);
rotate_plate(plate_angle);
//alert("msg : " + e_msg.data);
}
function rotate_plate(angle) {
var stepper = document.getElementById("stepper");
var ctx = stepper.getContext("2d");
ctx.clearRect(-PIVOT_X, -PIVOT_Y, CANVAS_WIDTH, CANVAS_HEIGHT);
ctx.rotate(-angle / 180 * Math.PI);
ctx.drawImage(plate_img, -PIVOT_X, -PIVOT_Y);
ctx.rotate(angle / 180 * Math.PI);
/*
Currently, the angle displayed and sent as a message appears to be set such that movement in a clockwise direction
reports a negative number. Needs to be looked at, probably by changing "angle.toFixed" to "-angle.toFixed"
*/
if(ws && (ws.readyState == 1))
ws.send(plate_angle.toFixed(4) + "\r\n");
ws_angle = document.getElementById("ws_angle");
ws_angle.innerHTML = angle.toFixed(1);
}
function check_update_xyra(event, mouse_xyra) {
var x, y, r, a;
var min_r, max_r, width;
if(event.touches) {
var touches = event.touches;
x = (touches[0].pageX - touches[0].target.offsetLeft) - PIVOT_X;
y = PIVOT_Y - (touches[0].pageY - touches[0].target.offsetTop);
}
else {
x = event.offsetX - PIVOT_X;
y = PIVOT_Y - event.offsetY;
}
/* cartesian to polar coordinate conversion */
r = Math.sqrt(x * x + y * y);
a = Math.atan2(y, x);
mouse_xyra.x = x;
mouse_xyra.y = y;
mouse_xyra.r = r;
mouse_xyra.a = a;
if((r >= MIN_TOUCH_RADIUS) && (r <= MAX_TOUCH_RADIUS))
return true;
else
return false;
}
function mouse_down(event) {
if(event.target == stepper)
event.preventDefault();
if(event.touches && (event.touches.length > 1))
click_state = event.touches.length;
if(click_state > 1)
return;
if(check_update_xyra(event, mouse_xyra)) {
click_state = 1;
last_angle_pos = mouse_xyra.a / Math.PI * 180.0;
}
}
function mouse_up() {
click_state = 0;
}
function mouse_move(event) {
var angle_pos, angle_offset;
if(event.touches && (event.touches.length > 1))
click_state = event.touches.length;
if(!click_state || (click_state > 1))
return;
if(!check_update_xyra(event, mouse_xyra)) {
click_state = 0;
return;
}
event.preventDefault();
angle_pos = mouse_xyra.a / Math.PI * 180.0;
if(angle_pos < 0.0)
angle_pos = angle_pos + 360.0;
angle_offset = angle_pos - last_angle_pos;
last_angle_pos = angle_pos;
if(angle_offset > 180.0)
angle_offset = -360.0 + angle_offset;
else
if(angle_offset < -180.0)
angle_offset = 360 + angle_offset;
plate_angle += angle_offset;
rotate_plate(plate_angle);
}
window.onload = init;
</script>
</head>
<body>
<h2>
Smart Expansion / Stepper Motor<br><br>
Angle <font id="ws_angle" color="blue">0</font><br><br>
<!--
<div class="container">
<div class="knob">
-->
<canvas id="stepper"></canvas>
<!--
</div>
</div>
-->
<br><br>
WebSocket <font id="ws_state" color="gray">CLOSED</font>
</h2>
<p><button id="bt_connect" type="button" onclick="connect_onclick();">Connect</button></p>
</body>
</html>
I might need to add an additional comment to give the link to the backgound image
knob_bg.png
knob_fg.png
So, after managing to find out how to debug html on an ios device via firefox on windows, I have managed to find out what was causing my code to fail.
The problem was in the function check_update_xyra(event, mouse_xyra)
Specifically the lines :
x = (touches[0].pageX - touches[0].target.offsetLeft) - PIVOT_X;
y = PIVOT_Y - (touches[0].pageY - touches[0].target.offsetTop);
The target.offsetxxx was returning a value of 0. This made the radian value (r) to be out of bounds which caused the function to return false, or in the case of the iPhone caused the touch event to behave strangely.
The reason for for the offsets coming back as 0 was because I did not factor in the fact that they provided the offset from the targets parent only, not the document as a whole.
I managed to fix this by adding some code to add the offsets for all parent elements then used that sum to calculate new x and y coordinates.
My code change follows.
However, if anyone has a more elegant method of calculating the offsets, I would appreciate it.
Cheers...
function check_update_xyra(event, mouse_xyra) {
var x, y, r, a;
var tgtoffleft = 0;
var tgtofftop = 0;
var min_r, max_r, width;
if(event.touches) {
var touches = event.touches;
// Bit of code to calculate the actual Left and Top offsets by adding offsets
// of each parent back through the hierarchy
var tgt = event.touches[0].target;
while (tgt) {
tgtoffleft = tgtoffleft + tgt.offsetLeft;
tgtofftop = tgtofftop + tgt.offsetTop;
tgt = tgt.offsetParent;
}
// x = (touches[0].pageX - touches[0].target.offsetLeft) - PIVOT_X;
// y = PIVOT_Y - (touches[0].pageY - touches[0].target.offsetTop);
x = (touches[0].pageX - tgtoffleft) - PIVOT_X;
y = PIVOT_Y - (touches[0].pageY - tgtofftop);
}
else {
x = event.offsetX - PIVOT_X;
y = PIVOT_Y - event.offsetY;
}
/* cartesian to polar coordinate conversion */
r = Math.sqrt(x * x + y * y);
a = Math.atan2(y, x);
mouse_xyra.x = x;
mouse_xyra.y = y;
mouse_xyra.r = r;
mouse_xyra.a = a;
if((r >= MIN_TOUCH_RADIUS) && (r <= MAX_TOUCH_RADIUS))
return true;
else
return false;
}
I'm using setInterval to call a function that animates a fractal on a HTML5 canvas. There is also a slider to allow the user to change the quality of the fractal. Everything works fine until I start changing the slider. When I change it, the fractal animation becomes choppy, and eventually the "drawFractal" function stops being called.
Here is the slider HTML:
<input type="range" id="qualitySlider" min="1" max="10"></input>
Here is the javascript (it just generates a fractal):
var count = 0.5;
var slider = document.getElementById("qualitySlider");
var g = document.getElementById("drawingCanvas").getContext("2d");
function drawFractal() {
var cellSize = Math.ceil(slider.value);
//canvas is 700 by 400
g.fillStyle = "black";
g.clearRect(0, 0, 700, 400);
//Eveything from here to the end of this function generates the fractal
var imagC = Math.cos(count)*0.8;
var realC = Math.sin(count)*0.5;
for (x = 0; x < 700; x+=cellSize) {
for (y = 0; y < 400; y+=cellSize) {
var yCoord = (x / 700.0 - 0.5)*3;
var xCoord = (y / 400.0 - 0.5)*3;
var real = xCoord;
var imag = yCoord;
var broken = 0;
for (i = 0; i < 8; i++) {
var temp = real*real - imag*imag + realC;
imag = 2*imag*real + imagC;
real = temp;
if (real*real + imag*imag >= 4) {
broken = true;
break;
}
}
if (!broken) {
g.fillRect(x, y, cellSize, cellSize);
}
}
}
count = count + 0.04;
}
setInterval(drawFractal, 60);
I just need the "drawFractal" function to be called reliably every 60 milliseconds.
This is my improved code. I just used requestAnimationFrame to recursively call the "drawFractal" function. I also restricted the animation to 24 frames/sec with the setTimeout function.
var count = 0.5;
var qualitySlider = document.getElementById("qualitySlider");
var g = document.getElementById("drawingCanvas").getContext("2d");
function drawFractal() {
var cellSize = Math.ceil(qualitySlider.value);
//canvas is 700 by 400
g.fillStyle = "black";
g.clearRect(0, 0, 700, 400);
var imagC = Math.cos(count)*0.8;
var realC = Math.sin(count)*0.5;
for (x = 0; x < 700; x+=cellSize) {
for (y = 0; y < 400; y+=cellSize) {
var yCoord = (x / 700.0 - 0.5)*3;
var xCoord = (y / 400.0 - 0.5)*3;
var real = xCoord;
var imag = yCoord;
var broken = 0;
for (i = 0; i < 8; i++) {
var temp = real*real - imag*imag + realC;
imag = 2*imag*real + imagC;
real = temp;
if (real*real + imag*imag >= 4) {
broken = true;
break;
}
}
if (!broken) {
g.fillRect(x, y, cellSize, cellSize);
}
}
}
count = count + 0.04;
setTimeout(function() {
requestAnimationFrame(drawFractal);
}, 41);
}
drawFractal();
You are using setInterval() to call drawFractal every 60 ms, and then every time drawFractal is executed, you're calling setInterval() again, which is unnecessary. You now have two timers attempting to draw fractals every 60 ms... then you'll have 4, then 8, etc.
You need to either (1) call setInterval() once at the start of program execution and not call it again, or (2) switch to using setTimeout(), and call it at the end of each drawFractal().
I'd use the second option, just in case your fractal ever takes more than 60 ms to draw.
I'm working on the project where I need to do some kind of screen calibration.
This calibration works in the way that when the plus button is pressed "credit card" is zoomed in and when the minus button is pressed it is zoomed out for 0.5mm.
Everything works fine but when button is clicked "credit card" is just zoomed in or zoomed out for 0.5mm, so I need to keep clicking to change zoom further. I want zoom to be constant when mouse key is pressed and to stop zooming when released.
There is my JavaScript code:
var c = document.querySelector('.card'),
m = document.querySelector('.m'),
p = document.querySelector('.p'),
s = document.querySelector('.s'),
r = document.querySelector('.r'),
w = c.style.width = '54mm';
m.addEventListener('click', function() {
w = c.style.width = parseFloat(w) - 0.5 + 'mm';
});
p.addEventListener('click', function() {
w = c.style.width = parseFloat(w) + 0.5 + 'mm';
});
s.addEventListener('click', function() {
r.innerHTML = 54 / parseFloat(w);
});
You can look at JSFiddle to see the code that I'm using now. Can somebody help me with the integration of this function in the existing code?
You need to setup event listeners a little bit different. This is my solution - I belive it's quite clear:
var c = document.querySelector('.card'),
m = document.querySelector('.m'),
p = document.querySelector('.p'),
s = document.querySelector('.s'),
r = document.querySelector('.r'),
w = c.style.width = '54mm';
var min = false;
var max = false;
m.addEventListener('mousedown', function(event) {
min = true;
});
m.addEventListener('mouseup', function(event) {
min = false;
});
p.addEventListener('mousedown', function() {
max = true;
});
p.addEventListener('mouseup', function() {
max = false;
});
s.addEventListener('click', function() {
r.innerHTML = 54 / parseFloat(w);
});
setInterval(function() {
if(min) {
w = c.style.width = parseFloat(w) - 0.5 + 'mm';
}
}, 100);
setInterval(function() {
if(max) {
w = c.style.width = parseFloat(w) + 0.5 + 'mm';
}
},100);
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;
};
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.