Develop Reference

How multiple canvas elements affect performance?

I'm trying to make a simple game (view from above) on canvas. Please tell me, which is faster:
1) Draw everything on one <canvas> and calculate the areas that need to be redrawn.
2) Draw certain parts of the scene on different <canvas> elements and update each only if necessary. In the it variant, probably, I can also use a partial redraw.
For example, I could draw a map on one element, enemies on the second, and a cursor and etc on the third. When moving enemies, I could only redraw the second canvas.
Please explain in as much detail as possible which option is better and why. And could you please advise books that can deepen my knowledge on this issue? For beginners.

Most canvas games will use a sort of layering that you are describing. The furthest forward layer would be the HUD, either by a seperate canvas or HTML elements and this would only change if something happened to it, such as someone upgrading their player. Then after that it depends on how they draw the canvas. The simplest way would be to simply draw the portions of the map and obstacles are on the screen.

Use one canvas, trust me. If you have a sprite that does nothing but sit there it is still getting drawn 60 times a second so it makes no difference if it is moving or not changing or not if it exists on screen it is getting drawn regardless of change.

Can this sequence be done in HTML5?

I certainly don't expect anyone to actually provide a working solution for this. My question at this point is a simple one: can this be done with an HTML5 canvas, or would I be spinning my wheels in the attempt?
I'm a programmer, but my forte is in PHP, JavaScript, traditional HTML, etc. ...I haven't had a chance to play with HTML5 yet.
The elements you see in the example, I can save out as individually as necessary. So to make the blocks rotate around the center, I was thinking I save a square image with the block in the appropriate corner, respectively. Then rotating the image would pivot around center appropriately, unless you can set a point of origin on an image a la PhotoShop.
The KineticJS library looks promising for this type of animation as well, but I'll leave the recommendations to you fine folks.
Anyway, here is the example I want to replicate:

I won't give any library recommendations for the same reasons that #Diodeus points out, but maybe I can help your selection process. What you're trying to do can be done multiple ways in the browser right now: Canvas, SVG, and/or CSS3 animations.
Your example above is basically a few vector graphics composed together with a gradient on your center "pie timer". Because of this I would lean towards using S V G, especially if you want to allow interactions with your component (each SVG element can have event handlers).
The canvas element is better for "pixel by pixel" control of your visual content on the page. Adding content in the canvas doesn't grow the DOM (like with SVG) so it will normally perform better, but you lose things like native event handlers and animations that you will end up having to re-implement on your own.
More about the choice between SVG and Canvas, and an SVG animation example
Once you have the components in the page, they'll need to be wired up and animated. The animation can be broken down into:
Scaling
Background color fading
Rotation
"Weird gradient pie timer" example with CSS3
These can be done with CSS animations, SVG animations, or with plain old javascript. The choice depends on what you'll be animating. If I was selecting a library I would want to find one that tried to use the newer methods (SVG/CSS3) when it can, and gracefully degrade when it cannot.
I would be weary of libraries that try to re-implement things that are already available natively in the browser. Relying more on the browser instead of your own code to do things like animations means that the browser can optimize its operations and use things like hardware acceleration to improve your performance.
Hopefully this can aid your library selection. Remember, libraries come and go all the time so don't get too attached to one. An ideal implementation should allow for you to easily swap out your animation or display code without having to touch other unrelated pieces.

Sure, it's not all that difficult when you break it down into pieces.
Here are some technologies and techniques to get you started.
You use Canvas by (1) displaying some drawings, (2) erasing, (3) displaying some new drawings
When you do this redrawing rapidly, you get animated effects like your image shows.
Html Canvas uses a context to draw with (think of it as the pen for the canvas)
drawing a path: context.beginPath + context.moveTo + context.lineTo will define a path that creates your "fan blade" polygons. You can use context.fillStyle to fill the polygons with you colors.
fading: context.globalAlpha will change the opacity of new drawings
rotating: context.translate(centerX,centerY) + context.rotate(radianAngle) will rotate new drawings (like your rotating polygons, your tick-marks, )
scaling: context.translate(centerX,centerY) + context.scale(scaleX,scaleY) will scale your polygons.
arcs: context.arc(centerX,centerY,radius,beginningAngle,endingAngle) will draw an arc with a specified centerpoint and sweeping from a beginning angle to an ending angle.
math: circleCircumferenceX = centerX+radius*Math.cos(radianAngle) circleCircumferenceY = centerY+radius*Math.sin(radianAngle) uses trigonometry to calculate an xy coordinate on the circumference of a circle. You can combine this trig + Math.random to place your "speckles" in an arc around your centerpoint.

Spinning wheel or 360 degree rotation wheel

I am looking for some jquery plugin or any code examples for multiple spinning wheels or 360 degree rotation wheels. Attached is the demo image for which, I am looking for the solution, where all the wheel can be rotate and This is basically develop birthdate selection somewhat like desktop and mobile application...But I need for my web application. I am using PHP & Apache web server.
Thanks in advance for any idea or sameple code or similer solution to moving forward
-Himanshu

I don't know of any ready made solutions, but I can point you in two directions you can go:
You can make an image for each of the 3 different wheels with the correct sizes and next use css3 transformations to rotate the specific wheels with javascript ( https://developer.mozilla.org/en/CSS/transform#rotate )
The other option is to look into the html5 canvas tag and draw the wheels onto it by hand. Here is a tutorial which covers making a roulette game on a canvas tag, which is quite different from your requirements, but does describe the necessary techniques. http://www.switchonthecode.com/tutorials/creating-a-roulette-wheel-using-html5-canvas

Yes HTML5 canvas rotate() is the way to go with this. My site http://www.dougtesting.net has a winning wheel that uses canvas rotation, but only for one wheel image. The code is fully commented so you may find it a useful starting point.
For your project you would probably need multiple images that are rendered to the canvas and rotated to the desired angles. Also you will probably need to look in to a mouseDown, mouseMove, and mouseUp code to allow the user to drag the wheels to the desired locations, with the code being able to tell you the values pointed at (something the code in my winning wheel can also do).

I am not aware of a jQuery plugin that does exactly what you ask. In terms of browser compatibility, I recommend you to take a look at the excellent RaphaelJS JavaScript library. It allows you to draw and rotate a wheel using vector graphics. Best of all, this library is IE6+ compatible and works in most if not all modern webbrowsers, including tablets and mobile phones.
To ease the creation of the necessary vector graphics, you can draw the wheel in a vector image editor of your choice (e.g. Illustrator, Inkscape, etc..) and save the vector image as SVG file. A very convenient online companion tool called ReadySetRaphael takes an SVG file as input and produces the necessary JavaScript to draw the graphics automatically.
If you have the path of the vector graphic as an object in JavaScript, it is easy to rotate it with the Element.rotate() method.

Although I am not sure if a plugin exists for this purpose;In my current project we have made a context menu using the canvas api which is not that different from your requirement, if not a bit more complex. Therefore, I highly recommend using the HTML5 Canvas api to do this, if you are not restricted from it. You can use a few ideas from the interactive flower tutorial.
http://www.html5canvastutorials.com/labs/html5-canvas-interactive-flower/
This should help too if you're interested in bringing jQuery into play.
http://www.elated.com/res/File/articles/development/javascript/snazzy-animated-pie-chart-html5-jquery/

Adding sizing handles to drawn object in canvas

I have a full screen canvas I am drawing to, and I've set it up to allow the user to drag and drop objects that are within the canvas.
I also want to enable them to select an object, and then 'resize handlers' show up (the little circles in the corners) to allow them to click/drag and resize them.
I can code this manually by drawing circles in each corner and detect a click, etc.... but was wondering if anyone has any better way to do this? Maybe there's a library out there that already handles this?
Any help is appreciated!

There isn't any simpler way than doing it yourself or getting a library to do it for you.
I wrote a tutorial here on the use of sizing handles. That should get you started if you plan to make your own.

Redraw lots of objects on Canvas HTML

Is there a quick and efficient way to move lots of objects in canvas? Basically if there are around 1000 objects and I want to move all of them at once to emulate scrolling, it is very slow to redraw every single object by calling drawImage() 1000+ times.
Is there anyway to optimize this? I have an example link of the problem (and that's only with 100 objects): http://craftyjs.com/isometric/

Since canvas doesn't provide fast low level bitmap copying it's hard to do stuff in multiple layers and scroll for example the whole background at once and then only render the edges.
So what can you do? In short, nothing. Especially not when scrolling, sure you can do tricks with multiple canvases when you have a more or less static background but for moving objects there are hardly any performance improving tricks.
So, you've go to wait for Hardware Acceleration shipping in all majors browsers, I know this sounds ridiculous but I'm too waiting for that :/
The problem is that the canvas was never designed for game stuff. It was designed as, well, basically some kind of on the fly drawing thing, guess the designers had Photoshop clones in mind, but definitely not games, let alone the fact that there's no fast clear operation proves that, there's not even optimization in place when clearing the whole canvas with the same color.

If the images are already composited, not moving relative to one another, and defined by a rectangular region, then using canvas.drawImage() with a canvas as the first parameter and drawing to a sub-region should be significantly faster than re-drawing all the objects.
You could also just layer multiple canvases and slide the top canvas with the objects in HTML to scroll them.
Edit: Having really looked at your example, it seems to me that it should be implemented similar to Google Maps: create tiles of canvases and slide them left/right on the HTML page; once a canvas has been slid off the screen entirely (for example, off the left edge), move it to the other side (to the right edge) and re-use it for drawing. With this you will only need to re-draw whatever objects overlap the canvases that are moving on the edges.

You can draw all objects on a second, off-screen canvas and then only blit the whole canvas (drawImage() accepts canvas element).
However, if you're targeting desktop browsers, then this shouldn't be necessary. I've implemented tile engine (source) that simply redraws whole scene and naive implementation turned out to be pretty fast.

What I did to solve this problem was I had 10 squares on my screen and I wanted to animate them on a white background. So I drew a white rectangle over the canvas to clear the canvas so the animation would work. Does that make sense?
#Ivo By the way I read on http://www.w3.org/TR/html5/the-canvas-element.html that canvas was made for applications like games because it was a solution to get rid of the dependency on a external engine. Canvas is built in so it's kind of like a flash player built into your browser powered by JavaScript. I think it's fascinating.

You can use tiled rendering.
http://www.gamesfrommars.fr/demojsv2/ (better viewed with Chrome)