18th Feb 2009
Edit: Thanks to Kevin Luck for pointing out a flaw with the code in my original post (there was an extra assignment taking place, which caused the byte count to increase). Remove that and ternary will match if/else on a bytes-used basis. I’ll keep this post up here regardless, just ignore everything from this point on
16th Jan 2009
This evening I managed to find time to push a lot of updates through for PixelBlitz. This fixes some serious bugs that I introduced last year when trying to optimise the speed of the renderer. It also brings in new methods in the BlitzMath class (my favourite being the excellent wrapValue() function!), the new Box2D Physics classes (lots more on this to come) and the starting classes for BlitzGrid, BlitzDraw and BlitzWorld.
More importantly I’ve started putting the examples source code into Google Code, which I’ve tested and it all compiles against this latest build. So far all of my demos from last year are converted and working, including this new little Shoot-em-up Test. Use the cursor keys to move and control to fire. Firing doesn’t actually do anything, you can’t die, the aliens can’t die either, but I think it shows the potential speed a PixelBlitz game can have, and I’m not even starting to push it yet.
Get the latest release from Google Code including the rough and ready source for the demo game above, you’ll see the start of the new Collision Group system in there, which I’ll be evolving this year.
19th Sep 2008
Tonight I updated the PixelBlitz Engine with a small but significant feature. I attacked the issue of redundant redrawing of elements, and updated both the PixelSprite and RenderLayer classes so they no longer refresh all of their content if nothing has actually changed since the last render call.
Sounds simple and it is, but it makes a world of difference to the speed of things.
I’ve been researching how beneficial adding a dirty rect system in the engine would be. The problem I have is that it’s all dependant on the type of game. For example a vertical shooter, with a scrolling background and bullets flying everywhere, would have no benefit at all – if anything the extra calculations may even slow it down. But in a sedate game, especially one with large (overlapping) objects, it could be a dream.
So, still in two minds really – perhaps it’s something we allow the user to disable at will.
For now I’m going to optimise the 2DRenderer further by making it only copyPixels() from the area of the RenderLayer that has changed. At the moment it grabs a full sized layer even if the layer only contains say a 64×64 sprite somewhere.
Anyway until then the new code is available in svn.
19th Sep 2008
While planning some new routines for the PixelBlitz engine tonight one thing struck me – is it actually worth it?
There are a number of articles across the web about pixel blitting in AS3 (most of them at 8-bit Rocket but I did wonder if anyone had actually done some tests to see just what difference it makes in real-world terms.
After all, why mess around “blitting” things about if using a Sprite or MovieClip is just as fast anyway? Infact you could easily argue that using a native Flash display object gives you far more control (as you get to play with scaling, alpha, rotation, animation, sound events and more, easily).
Another thing also struck me – when building up the display for render the AVM will automatically use a dirty rectangles system. If you’ve got two overlapping movieclips then it won’t waste time drawing pixels that would otherwise be obscured by the one in front. Traditional blitting on the other hand doesn’t care about this, it’ll gleefully copyPixel() until the cows come home, pasting image after image on-top of each other (PixelBlitz suffers from this issue too).
[ Side note: It’s true we could add a similar dirty rectangles system to Pixel Blitz, to avoid copying data when it’s guaranteed to be overwritten further up the chain – but this is not something we’ve found a fast way to do yet (the potential alpha channel of a bitmap causing the most problems), the overhead of sorting and checking for overlaps is always taking longer than just brute-force copying everything each time (if you can help, email me!) ]
Tonight I decided to write two simple tests. They would measure the speed of the AVMs dirty rectangle system vs. raw bitmapdata copypixel power. I was interested in 3 things – the overall time it took to run the test, the amount of memory it used and the average fps rate.
I took a 550 x 400 sized stage published at 30 fps. All tests were run using the Debug version of the Player (9.0 r 124). The test consisted of creating an array of X number of sprites (to test the AVM) and PixelSprites (to test blitting). Each sprite was 50×50 in size and contained an alpha channel. I then drew all of the sprites onto the stage and moved them along by 4 pixels per frame, if they hit the left of the stage they wrapped around to the right again. The Sprites had cacheAsBitmap set to true (see note below)
Then I ran the tests multiple times, with varying numbers of fish, for varying durations, recording the data at each step and averaging it out.
I agree that this is in no way a truly “scientific” test, but I wanted a general “feeling” as a result, to see if this was an avenue still worth walking down or not.
With 500 sprites both the standard Sprite and the blit method kept a solid 30 fps frame rate. Using Sprites consumed 15MB of RAM, using blits 11MB.
At 1000 sprites we’re still at a consistent 30 fps, but there is noticeable “tearing” in the visuals as the sprites move across the stage. It’s not terrible, but you can easily see it. The standard method is now using 20MB while the blit is using 14MB.
2500 sprites and we see both techniques struggle to keep-up with the 30 fps rate. The traditional Sprites actually outpace the blitting at 23 fps vs 21 fps, but the memory consumption is more than doubled, 35MB vs. 15MB.
At 5000 sprites they are both starting to feel the strain, each level pegging at 12 fps. But the standard Sprites technique is using a staggering 58MB, while the blit is only up to 20MB.
7,500 sprites all moving at once and both techiques are virtually bought to their knees managing just 8 fps each. Given the amount of data moving this isn’t totally surprising. The blit technique at this point is literally copying 18.7 million pixels around in memory. The AVMs internal dirty rectangle is feeling the full force of what’s going on however, and is now consuming 237MB of RAM vs. the blit techniques 25MB.
10,000 sprites crashes the Debug player for both versions, it literally runs out of memory
As I mentioned at the start, the Sprite version had cacheAsBitmap set to true. This is the main cause of the huge amount of RAM being used. As our Sprite only contained a single Bitmap this wasn’t needed. By removing this setting the amount of RAM used dropped, ending up only a few MB higher than the straight blit method.
So what can we pull from this?
First of all, the AVM dirty rectangles implementation is pretty damn sweet! But brute-force blitting is equally as fast in this test case. Logic tells us that adding redraw aware optimisation to our blit engine should increase this gap in our favour significantly.
NEVER enable cacheAsBitmap on a Sprite or MovieClip if all it contains is bitmap data.
The blit engine uses less memory. If you need to cache vector Sprites in your game, then it uses considerably less memory!
No-one really needs a game with 7,500 fish swimming around in it 😉
Maybe the test wasn’t “real world” enough – even at the 1000 sprite level (at which both methods kept a 30 fps frame rate) we were still moving 2.5 million pixels around a 550 x 400 stage. That’s enough to fill the stage 11 times over (and still have some spare). Is this likely in a real game? Well no, I don’t believe so – but it isn’t that far off either. Games are getting bigger (we published one at 800×600 today for example), and if you had a game featuring multiple layers going on (foreground, player, background, distance, etc) with alpha showing through them all, then it doesn’t take long to start using pixels in the millions range.
There are instances when I believe it’s just easier to deal with things on a blit level – for example building up a large n-way scrolling tilemap, where you constantly need to redraw the scroll buffers. Doing the same by placing (and updating) hundreds of Sprites would be an exercise in pain I wouldn’t wish on anyone.
Is a combination of both worlds the way to go? Quite possibly. While I loathe using the timeline (or Movieclips in general) for anything, they do offer Flash animators a rich featured tool-set that let’s them create vibrant moving games. Whereas the blit method requires graphic artists trained in the way of the pixel, and I believe those are a dying (and expensive) breed indeed. Creating quality animations at that level is time-consuming and costly. But as we’ve seen, animating on a vector level introduces both resource and speed issues into your game.
What about collision detection? Well we all know this pretty much sucks in Flash. So we have to roll our own methods anyway. For pixel perfect collision detection we need to inspect the elements on a pixel level (surprise surprise), at least with the blit technique we’re already operating on that level, so there’s no extra draw() overhead involved.
Are AS3 Sprites “evil” for those of you trying to create arcade style games? No, I don’t believe so. They can hold their own in the speed stakes thanks to the power of the AVM, but you do have to watch yourself and be very careful re: memory consumption.
Is “blitting” really that much faster the using normal Sprites? No, it isn’t. It does have less memory overhead and a “cleaner” feel to it, but it’s no speed demon in comparison.
Would a hybrid solution work? (i.e. a fully blitted tilemap with Movieclips characters on-top) – yes, absolutely!
Don’t feel that because you have travelled down the “blit” route you need to have the whole game living there. If you can mix and match your game logic and most importantly your collision systems, then there’s no harm in splitting these elements up, using both at once.
P.S. If you’ve got some ideas or concepts on optimising blit level drawing, please get in touch. I’ve been reading a lot about this recently (what I can find at least) but it’s always good to pick someone’s brain.
16th Sep 2008
sergej wrote a comment to my BlitzMouse post saying that if you right-clicked the custom pointer gets lost until the page is refreshed. Here is some simple code to work around this.
In your main SWF make sure you import ContextMenu and ContextMenuEvent. Then add 2 new global vars:
private var rightClickContext:ContextMenu;
private var contextOpen:Boolean;
and within your init (or constructor) add this:
rightClickContext = new ContextMenu();
this.contextMenu = rightClickContext;
rightClickContext.addEventListener(ContextMenuEvent.MENU_SELECT, contextMenuOpen, false, 0, true);
“this” is a Sprite in this case, but any valid display object (that has access to the contextMenu) will do. The “contextMenuOpen” function is literally just the following:
private function contextMenuOpen(event:ContextMenuEvent):void
contextOpen = true;
and finally, in your main game loop, just check the state of this var and reset accordingly:
if (contextOpen && mouse.isDown)
When the context menu is opened (by a right-click on Windows) it fires the ContextMenuEvent.MENU_SELECT event, which we capture and set a boolean for accordingly. While the menu is open we can do nothing about the standard mouse pointer, but in our main loop we can listen out for a mouse click (mouse.isDown) and then hide the pointer again accordingly.
I’ve not tested this on a Mac (where you can command-click to get the context menu up) so if anyone reading can do so, please let me know if it works.
The SWF below should allow you access to the context menu, but upon clicking the SWF again the custom pointer should return (assuming you click within the limit zone!)
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