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I'm writing an application where I will need a number of full screen bitmap backgrounds. Based on my naive reading of Supporting Multiple Screens in the Android documentation, to cover all my bases I should probably have 16 versions of each bitmap: all pairs of [ small, normal, large, xlarge ] and [ ldpi, mdpi, hdpi, xhdpi ]. This should reduce the work the CPU has to do for scaling the images, but will come at great storage cost.

However, this seems wildly inefficient for two reasons:

  1. Not all of these combinations are found in practice.
  2. As I'm just rendering vector art for each physical size (without respect for DPI), pairs like large/mdpi and normal/hdpi (which are both ~ 480x854 pixels) are duplicate files.

So, should I just provide really large images and let the system scale them down? Bite the bullet and provide a lot of duplicate images? Avoid the issue altogether and cobble some code solution with raw resources? Any other ideas? Thanks.

EDIT: Apparently you can create XML bitmap drawables which alias an actual bitmap. That solves the second inefficiency argument. Still, I wonder, what combinations of these do others provide in practice?

Hilton Campbell
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You would only provide images at different resolutions if you want that piece of art to be a constant size, regardless of the screen dpi it is displayed on. An icon or a button would be an example of this.

For the background images described here, you don't care what the image dpi is -- you only care what the x * y dimensions are. So you don't have to produce the cross-product of sizes vs. dpi. You only need consider the 4 screen size categories.

And within the 4 screen size categories, you only need store one of the larger sizes (xlarge or large) and let the framework scale that up or down as needed. You can also do the scaling programmatically, to ensure that you don't change the aspect ratio of your background, and you don't crop it.

See also Android game working on all screen sizes which will hopefully attract a better answer.

Community
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Peter vdL
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I would advise providing images for ldpi, mdpi, hdpi and optionally xhdpi (depending on your target users). That will allow you to cover the most commonly used resolutions just fine.

If you end up with the feeling that your application is getting too large (either by deciding to add all possible image sizes or other reasons), you can also look into allowing your application to be moved to an SD card. That way, storage won't be much of an issue anymore. (http://developer.android.com/guide/appendix/install-location.html)

tvkanters
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  • I'm worried that the size of the application itself will be too large. At what size should I provide these images? I don't want the OS to ever have to enlarge any of the drawables on any device. – Hilton Campbell Mar 22 '11 at 17:34