SpriteKit Texture Atlas vs Image xcassets - ios

Question

I am making a game and I noticed that during some scenes, my FPS kept dropping around the 55-60FPS area (using texture atlas). This drove me nuts so I decided to put all my assets to the Images.xcassets folder and voila, steady 60FPS.
I thought this was a fluke or that I was doing something wrong, so I decided to start a new project and perform some benchmarks...
Apple's documentation says that using texture atlas's will improve app performance. Basically, allowing your app to take advantage of batch rendering. However...
The Test (https://github.com/JRam13/JSGlitch):
- (void)runTest
{
SKAction *spawn = [SKAction runBlock:^{
for (int i=0; i<10; i++) {
SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:#"Spaceship"];
sprite.xScale = 0.5;
sprite.yScale = 0.5;
sprite.position = CGPointMake(0, [self randomNumberBetweenMin:0 andMax:768]);
SKAction *action = [SKAction rotateByAngle:M_PI duration:1];
[sprite runAction:[SKAction repeatActionForever:action]];
SKAction *move = [SKAction moveByX:1200 y:0 duration:2];
[sprite runAction:move];
//notice I don't remove from parent (see test2 below)
[self addChild:sprite];
}
}];
SKAction *wait = [SKAction waitForDuration:.1];
SKAction *sequence = [SKAction sequence:#[spawn,wait]];
SKAction *repeat = [SKAction repeatActionForever:sequence];
[self runAction:repeat];
}
Results:
Tests repeatedly show that using the xcassets performed way better than the atlas counterpart in FPS. The atlas does seem to manage memory marginally better than the xcassets though.
Anybody know why these results show that images.xcassets has better performance than the atlas?
Some hypotheses I've come up with:
xcassets is just better optimized than atlasas.
atlasas are good at drawing lots of images in one draw pass, but have bigger overhead with repeated sprites. If true, this means that if your sprite appears multiple times on screen (which was the case in my original game), it is better to remove it from the atlas.
atlas sheets must be filled in order to optimize performance
Update
For this next test I went ahead and removed the sprite from parent after it goes offscreen. I also used 7 different images. We should see a huge performance gain using atlas due to the draw count but...

Answer 1

First, revise your test to match this :
for (int i=0; i<10; i++) {
SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:#"Spaceship"];
sprite.xScale = 0.5;
sprite.yScale = 0.5;
float spawnY = arc4random() % 768;
sprite.position = CGPointMake(0, spawnY);
SKAction *action = [SKAction rotateByAngle:M_PI duration:1];
[sprite runAction:[SKAction repeatActionForever:action]];
SKAction *move = [SKAction moveByX:1200 y:0 duration:2];
// next three lines replace the runAction line for move
SKAction *remove = [SKAction removeFromParent];
SKAction *sequence = [SKAction sequence:#[move, remove]];
[sprite runAction:sequence];
[self addChild:sprite];
}
Rerun your tests and you should notice that your framerate NEVER deteriorates as in your tests. Your tests were basically illustrating what happens when you never remove nodes, but keep creating new ones.
Next, add the following line to your ViewController when you set up your skview :
skView.showsDrawCount = YES;
This will allow you to see the draw count and properly understand where you are getting your performance boost with SKTextureAtlas.
Now, instead of having just one image , gather 3 images and modify your test by choosing a random one of those images each time it creates a node, you can do it something like this :
NSArray *imageNames = #[#"image-0", #"image-1", #"image-2"];
NSString *imageName = imageNames[arc4random() % imageNames.count];
In your code, create your sprite with that imageName each time through the loop. ie :
SKSpriteNode *sprite = [SKSpriteNode spriteNodeWithImageNamed:imageName];
In your SKTextureAtlas test, use that same imageName obviously to create each sprite.
Now... rerun your tests and take note of the draw count in each test.
This should give you a tangible example of what batch rendering is about with SKTextureAtlas.
It's no about rendering the same sprite image thousands of times.
It's about drawing many different sprites images in the same draw pass.
There is likely some overhead in getting this rendering optimization, but I think the draw count should be self explanatory as to why that overhead is moot when all things are considered.
Now, you can hypothesize some more :)
UPDATE
As mentioned in the comments, my post was to expose why your test was not a good test for the benefits of SKTextureAtlas and was flawed if looking to analyze it in a meaningful way. Your test was like testing for measles with a mumps test.
Below is a github project that I put together to pinpoint where an SKTextureAtlas is appropriate and indeed superior to xcassets.
atlas-comparison
Just run the project on your device and then tap to toggle between tests. You can tell when it's testing with SKTextureAtlas because the draw count will be 1 and the framerate will be 60fps.
I isolated what will be optimized with a SKTextureAtlas. It's a 60 frame animation and 1600 nodes playing that animation. I offset their start frames so that they all aren't on the same frame at the same time. I also kept everything uniform for both tests, so that it's a direct comparison.
It's not accurate for someone to think that using SKTextureAtlas will just optimize all rendering. It's optimization comes by reducing draw count via batch rendering. So, if your framerate slowdown is not something that can be improved via batch rendering, SKTexture atlas is the wrong tool for the job. right ?
Similar to pooling of objects, where you can gain optimization via not creating and killing your game objects constantly, but instead reusing them from a pool of objects. However if you are not constantly creating and killing objects in your game, pooling ain't gonna optimize your game.
Based on what I saw you describe as your game's issue in the discussion log , pooling is probably the right tool for the job in your case.