Universal 2D Game Assets and Absolute Node Positioning

Question

I have a question regarding universal game assets and absolute positioning of a SKNodes in Sprite Kit (iOS 8+).

I will try to present my problem through an example as follows:

Imagine a 2D top down game with a SKSpriteNode which represents a house. A house has multiple child SKSpriteNodes which represent chairs, desk, sofa, etc.

I have 3 versions of house asset:

• 1x - 200 x 200px (Non-retina iPads),
• 2x - 400 x 400px (Retina iPhones and iPads),
• 3x - 600 x 600px (iPhone 6 Plus).

Important: Child nodes (chairs, desk, etc.) positions are defined in a .plist file. Something like this (JSON representation):

children: [
    {
        position = {20,20};
    },
    ...
]

Since the position is defined in points and not in pixels, everything gets positioned like expected according to device screen scale. For 1x devices the position stays {20,20}, for 2x position is {40,40} and for 3x the position is {60,60}.

Problem:

The problem is that 200x200px and 400x400px assets are way to small for iPad devices in order to achieve similar look and feel on all devices.

Question:

How to successfully present/import assets in a way that would enable me to achieve similar (if not the same) look and feel on all devices/screen sizes without breaking child nodes positioning?

My takes:

Take 1:

I could simply use the existing 400x400px assets on Non-retina iPad devices and 600x600px assets on Retina iPad devices for the house node but the positioning of a child nodes would become broken. This is because the child position value wouldn't change and would still be {20,20} and {40,40} for iPad devices respectively, while the assets would be bigger. This would yield inaccurate child positions relative to the house node.

Take 2:

I could also scale the SKScene size (zoom effect) while using the normal 200x200px and 400x400px sized assets for iPad devices respectively. This works and it keeps the child nodes positioning working but the rendered quality of the scene/assets is not good as it should be. Also, this feels like a hack and we don't want that.

Take 3:

I could also use twice as big assets for iPad devices and double the child nodes position at the runtime. In this case I would use a 400x400px asset for non-retina iPad devices and a new 800x800px asset for retina iPad devices. While this looks great and keeps the child nodes positioning working, it seems like a really big hack fixing child node position during runtime with this:

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    position.x *= 2.0f;
    position.y *= 2.0f;
}

---

Thank you for taking the time to read the question!

Answer 1

I could simply use the existing 400x400px assets on Non-retina iPad devices and 600x600px assets on Retina iPad devices for the house node but the positioning of a child nodes would become broken. This is because the child position value wouldn't change and would still be {20,20} and {40,40} for iPad devices respectively, while the assets would be bigger. This would yield inaccurate child positions relative to the house node.

You can simply scale your house node (not the scene) to a larger size. All you need to do is set the scale on your house to a value that looks good on larger devices. And in fact, instead of checking for iPad we can come up with a formula that sets the scale depending on the size of the screen. Something like the code below should work. Note that it assumes your house is positioned perfectly on a iPhone 4 and it will consistently scale to all larger screens. Note that you really could pick any arbitrary size as your base case, but choosing the smallest screen and scaling up is easiest. Just be sure to provide larger textures so that the textures don't become blurry when scaled.

[house setScale:self.scene.size.width/320.0];

OR

You could use two nodes. A root node for holding the "actual" position, and then an image node child for displaying the image. This will allow you to separate your positional data from what's being displayed. You could resize and position your child image node however you want without messing with the actual position of the root node. You could even include this extra image node data in your JSON.

---

I could also scale the SKScene size (zoom effect) while using the normal 200x200px and 400x400px sized assets for iPad devices respectively. This works and it keeps the child nodes positioning working but the rendered quality of the scene/assets is not good as it should be. Also, this feels like a hack and we don't want that.

This option can definitely work if your App can handle the different aspect ratios in someway. For example you could allow scrolling the scene if the scene is scaled larger than the device screen. The loss in quality occurs because you are scaling the textures larger than their expected size. You need to provide larger textures to keep the quality high when zooming. In this case you could probably just use your 600x600 images (or maybe even larger) and let it scale with zoom. For example, in my RTS Sprite-Kit game for OS X I scale the entire scene so I get the same look across all devices. And I don't lose any quality because I make sure to provide very large textures so there is no loss in quality while scaling.

---

I could also use twice as big assets for iPad devices and double the child nodes position at the runtime. In this case I would use a 400x400px asset for non-retina iPad devices and a new 800x800px asset for retina iPad devices. While this looks great and keeps the child nodes positioning working, it seems like a really big hack fixing child node position during runtime with this:

This could also work, especially if your iPad requires custom layout. However, if possible avoid checking specifically for iPad and instead use the screen size to create layout rules so your nodes dynamically adjust on all screen sizes consistently (See the line of code above). Sometimes this is not possible if your iPad layout is very different from the iPhone, in which case you will have no choice but to check for iPad.

---

All three of these solution are good. I wouldn't consider any one of them "hacky." They all work for different purposes. You need to find the solution that works best for your game.

I would also recommend you see my two answers below. Not sure but they may help you with understanding universal positioning and scaling in Sprite Kit.

https://stackoverflow.com/a/25256339/2158465

https://stackoverflow.com/a/29171224/2158465

Good luck with your game, let me know if you have any questions.

Answer 2

There's no easy way to do what you want. One approach would be to use a fixed screen size on your devices. The iPhone 5 all the way up to iPhone 6+ all use a 16:9 aspect ratio for their screens. Whereas the iPad and iPhones 4s and earlier, all use a 4:3 screen aspect ratio.

Before presenting your GameScene, you can determine the screen's aspect ratio and then set a fixed view size like this for 16:9:

GameScene *startGame = [[GameScene alloc] initWithSize:CGSizeMake(736, 414)];
startGame.scaleMode = SKSceneScaleModeAspectFit;

or this for 4:3

GameScene *startGame = [[GameScene alloc] initWithSize:CGSizeMake(1024, 768)];
startGame.scaleMode = SKSceneScaleModeAspectFit;

The exact values really do not matter, only the ratios.

Knowing the exact screen size will allow you to place objects in more precise manner regardless of iPhone 5 screen or 6+ screen.

Answer 3

Using image assets, you can also specify iPad versions of an image.

However there's not really a way around adding some extra logic to your app, branching depending on whether or not your running on the iPad, and adjusting the position manually.

We could discuss how to best incorporate that though: I'm not a fan of this "if I'm not this device" checks all throughout the code. Create an abstract superclass and two subclasses, each handling layout (or whatever you may want to call it) for one interface idiom. You will the only need to check once (when instantiating these) and polymorphism will take care of the rest.

Answer 4

You can use a software as PaintCode to dynamically generate texture perfectly sized to your need.

All you have to do is to define the frame' dimensions for each of your devices.