Develop Reference

JavaScript canvas game development

Ive been having a really baffling slow down issue with the game I am working on probably because I am unsure how to handle graphics (most likely responsible for the slow down) in javascript without using a third party framework like Phaser/ImapactJS/EaselJS etc)*. The following is the low down on how I am approaching my graphics. I would be very thankful for some tips or methods on how to do this right.
My game is tile based - using tiles designed at 500x500 px because I want them to display decently on high definition devices.
I am using a spritesheet to load all (most of) my tiles before the main loop is run. This image is roughly 4000 x 4000 (keeping it below 4096 because the GPU cant handle texture sizes larger than that).
I then use the drawImage function to cycle through and draw each tile on a part of the canvas using information (w, h, x, y) stored in the tile array. I do this on every cycle of the main loop using my drawMap function.
The map is currently 6x6 tiles in size
A character spritesheet is also loaded and drawn on to the canvas after the map has been drawn. The character displays a different frame of the animation on every cycle of the main loop. There are sets of animations for the character each contained in the same spritesheet.
The character sprite sheet is roughly 4000x3500
The character is roughly 350x250 px
Other objects also use the same sprite sheet. Currently there is only one object.
Possibly helpful questions:
Am I using too many spritesheets or too few?
Should I only draw something if it's coordinates are in bounds of the screen?
How should I go about garbage collection? Do I need to set image objects to null when no longer in use?
Thanks in advance for input. I would just like to know if I am going about it the right way and pick your brains as how to speed it up enough.
*Note that I plan to port the JS game to cocoonJS which provides graphics acceleration for the canvas element on mobile.
** If interested please visit my Patreon page for fun!

You have asked lots of questions here, I'll address the ones I've run into.
I would like to start out by saying very clearly,
Use a profiler
Find out whether each thing you are advised to do, by anybody, is making an improvement. Unless we work on your code, we can only give you theories on how to optimise it.
How should I go about garbage collection? Do I need to set image objects to null when no longer in use?
If you are no longer using an object, setting its reference to null will probably mean it gets garbage collected. Having nulls around is not necessarily good but this is not within the scope of this question.
For high performance applications, you want to avoid too much allocation and therefore too much garbage collection activity. See what your profiler says - the chrome profiler can tell you how much CPU time the garbage collector is taking up. You might be OK at the moment.
I then use the drawImage function to cycle through and draw each tile on a part of the canvas using information (w, h, x, y) stored in the tile array. I do this on every cycle of the main loop using my drawMap function.
This is quite slow - instead consider drawing the current on screen tiles to a background canvas, and then only drawing areas which were previously obscured.
For example, if your player walks to the left, there is going to be a lot of tiles on the left hand side of the screen which have come into view; you will need to draw the background buffer onto the screen, offset to account for the movement, and then draw the missing tiles.
My game is tile based - using tiles designed at 500x500 px because I want them to display decently on high definition devices
If I interpret this right, your tiles are 500x500px in diameter, and you are drawing a small number of these on screen. and then for devices without such a high resolution, the canvas renderer is going to be scaling these down. You really want to be drawing pixels 1:1 on each device.
Would you be able, instead, to have a larger number of smaller tiles on screen - thereby avoiding the extra drawing at the edges? Its likely that the tiles around the edges will sometimes draw only a few pixels of one edge, and the rest of the image will be cropped anyway, so why not break them up further?
Should I only draw something if it's coordinates are in bounds of the screen?
Yes, this is a very common and good optimisation to take. You'll find it makes a big difference.
Am I using too many spritesheets or too few?
I have found that when I have a small number of sprite sheets, the big performance hit is when I frequently switch between them. If during one draw phase, you draw all your characters from character_sheet.png and then draw all the plants from plant_sheet.png you'll be ok. Switching between them can cause lots of trouble and you'll see a slow down. You will know this is happening if your profiler tells you that drawImage is taking a big proportion of your frame.

How can I increase map rendering performance in HTML Canvas?

We are developing a web-based game. The map has a fixed size and is procedually generated.
At the moment, all these polygons are stored in one array and checked whether they should be drawn or not. This requires a lot of performance. Which is the best rendering / buffering solution for big maps?
What I've tried:
Quadtrees. Problem: Performance still not as great because there are so many polygons.
Drawing sections of the map to offscreen-canvases. A test run: http://norizon.ch/repo/buffered-map-rendering/ Problem: The browser crashes when trying to buffer that much data and such big images (maybe 2000x2000) still seem to perform badly on a canvas.

(posting comments as an answer for convenience)
One idea could be, when the user is translating the map, to re-use the part that will still be in view, and to draw only the stripe(s) that are no longer corrects.
I believe (do you confirm ?) that the most costly operation is the drawing, not to find which polygon to draw.
If so, you should use your QuadTree to find the polygons that are within the strips. Notice that, given Javascript's overhead, a simple 2D bucket that contains the polygons that are within a given (x,y) tile might be faster to use (if the cost of the quadtree is too high).
Now i have a doubt about the precise way you should do that, i'm afraid you'll have to experiment / benchmark, and maybe choose a prefered browser.
Problems :
• Copying a canvas on itself can be very slow depending on devices/Browsers. (might require to do 2 copy, in fact)
• Using an offscreen canvas can be very slow depending on devices/Browsers. (might not use hardware acceleration when off-screen).
If you are drawing things on top of the map, you can either use a secondary canvas on top of the map canvas, or you'll be forced to use an off-screen canvas that you'll copy on each frame.

I have tried a lot of things and this solution turned out to be the best for us.
Because our map has a fixed size, it is calculated server-side.
One big image atlas with all the required tiles will be loaded at the beginning of the game. For each image on the atlas, a seperate canvas is created. The client loads the whole map data into one two-dimensional array. The values determine, which tile has to be loaded. Maybe it would be even better if the map was drawn on a seperate canvas, so that only the stripes have to be painted. But the performance is really good, so we won't change that.
Three conclusions:
Images are fast. GetImageData is not!
JavaScript has not yet great support for multi threading, so we don't calculate the map client-side in game-time.
Quadtrees are fast. Arrays are faster.

Non-blocking "intersects" in KineticJs

I am in the middle of process of making a HTML5 game. Now I have a problem related to performance.
I have some irregular Shapes. So detecting if {x,y} is in the Shape or not using a custom function is near impossible(At least as I think).
There are two big Shapes, so I need to call Shape.intersects({x,y}) twice for multiple times per second to detect if current {x,y} is in the shape or not.
{x,y} are variable and are not touch/mouse events. So I can not use onmousemove,etc events.
Each twice call of Shape.intersects({x,y}) on Nexus 5 has a ~45ms overhead. ~45ms each 100ms! This make some hiccups in game experience.
The most straight solution is to make Shape.intersects({x,y}) non-blocking. But how? or do anyone have any idea around this problem?
I am using Kinetic v5.0.1
RESULT:
.intersects will re-generate the Shape in memory, this is why it is very costly. According the to the #MarkE answer below, using native canvas function context.isPointInPath(x, y) would be very efficient. But:
Note that this will only work for the last path (after using beginPath()). If you need to iterate several paths (ie. shapes) you need to re-construct the paths (no need to stroke or fill though). This is perhaps a reason why some don't use it.
Source: https://stackoverflow.com/a/17268669/172163
In my shapes, I had solid colors. Also there are multiple shapes dynamically generated. so I ended up with context.getImageData(x, y, 1, 1) to get the color of specific pixel, and if it is the color of my Shapes are not. It is more efficient than .intersects(). It costs only ~3ms.

Why intersects gives you a performance hit (pun intended!)
Internally, KineticJS uses context.getImageData to do hit-tests in the intersects method.
getImageData provides pixel-perfect hit testing but it's slow on mobile devices (as you've discovered).
To answer your question:
No, you cannot run KineticJS's internal methods on a background worker thread.
But...
If you really need to squeeze performance out of hit-testing, you can write your own custom hit-test.
One possibility for such a custom hit test would be to maintain 2 offscreen html5 canvas elements that mirror your 2 irregular shapes.
That way you can use canvas's context.isPointInPath(x,y) to do your hit-testing.
The importance is that isPointInPath uses GPU acceleration and is therefore quite fast.
If you feel ambitious you could even create an asynchronous background worker thread to execute isPointInPath while your UI thread continues.
You mention the Nexus5. You can spawn a background worker thread with Android's AsyncTask.
Your background task can return the results of your hit-test using it's onPostExecute(Result) callback which invokes on the UI thread.
http://developer.android.com/reference/android/os/AsyncTask.html
Good luck with your project!

Canvas optimization when pixel changes are known

I am currently working on a web application where only single pixel changes are known, which are implemented like an event:
function pixelChanged(x, y, color)
These need to be drawn to a canvas. I have tried two methods to accomplish this:
draw pixels directly with fillRect
memorize pixels and put them on the canvas with putImageData every few microseconds
Now both of these methods seem to have a poor performance. The first one results in many redraws, the second one redraws the whole image, even if only a little area changed.
My specific question is, if there is a better method to implement this (maybe something like 1., but in some way delayed ?).
And if not, which method of these should I prefer ? How can I optimize it in this case ?
Thanks in advance and best regards,
copy

The approach I took is to break a large image into an NxN grid and redraw the specific areas that have changed. I found a decent size that balances the # of redraws vs the size of a redraw to be around 50x50px. If you need the exact optimal number for maximum px/sec drawn, I have it somewhere from benchmarks.
So if you have a 60x60 change, you'd be re-drawing between 4 and 9 50x50 squares.

Checkout this article with different approaches for canvas-optimization. I'd suggest you to combine several optimizations and see how it goes. Please note that our eye doesn't recognize frequent pixel changes on big area, so it make sense to buffer your pixel changes and draw several changes at once. Also please note that browser need several milliseconds to apply your changes, so don't make interval too small.

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)