Since Android 4.3 (Jelly Bean) we can now make use of the res/mipmap
folders to store "mipmap" images.
For example, Chrome for Android stores its icons in these folders instead of the more normal res/drawable
folders.
How are these mipmap images different from the other familiar drawable images?
I see that in my manifest, we use the @mipmap/
qualifier, instead of @drawable/
, which makes sense given the resource folder name:
<activity
android:name=".MipmapDemp"
android:icon="@mipmap/ic_launcher" />
References:
The Android 4.3 APIs document has the following to say:
Using a mipmap as the source for your bitmap or drawable is a simple way to provide a quality image and various image scales, which can be particularly useful if you expect your image to be scaled during an animation.
Android 4.2 (API level 17) added support for mipmaps in the Bitmap class—Android swaps the mip images in your Bitmap when you've supplied a mipmap source and have enabled setHasMipMap(). Now in Android 4.3, you can enable mipmaps for a BitmapDrawable object as well, by providing a mipmap asset and setting the android:mipMap attribute in a bitmap resource file or by calling hasMipMap().
I don't see anything in there that helps me to understand.
XML Bitmap resources have an android:mipMap
property:
Boolean. Enables or disables the mipmap hint. See setHasMipMap() for more information. Default value is false.
This does not apply to launcher icons as far as I can see.
The question was raised on Google Groups (The purpose of resource name "mipmap"?!), to which Romain Guy replied:
It's useful to provide an image at a larger resolution that would normally be computed (for instance, on an mdpi device, Launcher might want the larger hdpi icon to display large app shortcuts.)
I feel like this almost makes sense of it, but not quite.
I'm still inclined to go with Randy Sugianto's follow up:
What are the advantages of this? Is there any guide how to use mipmaps, probably for better launcher icons?
Of course, Wikipedia has a page for "Mipmap", which refers to an older technique invented in 1983, that I can't quite relate to the current Android implementation.
Should we be storing all our app icons in res/mipmap
folders these days, and what are the guidelines for these mipmap images?
Update #1
Here's a blog post that tries to explain it a bit.
But the image used in that blog post shows what looks like one file with many logos in it. This is not what I see in Chrome's mipmap folder.
Chrome's mipmap-hdpi
folder contains three images. One is the Chrome logo, on its own.
Strangely, it is 72x72, not 48x48 which I would expect to see.
Perhaps that is all there is to this - we just need to keep bigger icons in the mipmap folders?
Update #2
The Android Developers Blog post of 23/10/2014 again confirms the idea of using the mipmap
folders for application icons:
When talking about the Nexus 6 screen density, the author writes:
It’s best practice to place your app icons in mipmap- folders (not the drawable- folders) because they are used at resolutions different from the device’s current density. For example, an xxxhdpi app icon can be used on the launcher for an xxhdpi device.
Update #3
Note that Android Studio creates the ic_launcher.png
icons in the mipmap...
folders rather than the drawable...
folders that Eclipse used to create them in.
Citation from this article.
https://plus.google.com/105051985738280261832/posts/QTA9McYan1L
The Android implementation of mipmaps in 4.3 is exactly the technique from 1983 explained in the Wikipedia article :)
Although this is described as a technique for 3D graphics (as it mentions "viewing from a distance"), it applies just as well to 2D (translated as "drawn is a smaller space", i.e. "downscaled").
For a concrete Android example, imagine you have a View with a certain background drawable (in particular, a
BitmapDrawable
). You now use an animation to scale it to 0.15 of its original size. Normally, this would require downscaling the background bitmap for each frame. This "extreme" downscaling, however, may produce visual artifacts.You can, however, provide a mipmap, which means that the image is already pre-rendered for a few specific scales (let's say 1.0, 0.5, and 0.25). Whenever the animation "crosses" the 0.5 threshold, instead of continuing to downscale the original, 1.0-sized image, it will switch to the 0.5 image and downscale it, which should provide a better result. And so forth as the animation continues.
This is a bit theoretical, since it's actually done by the renderer. According to the source of the Bitmap class, it's just a hint, and the renderer may or may not honor it.
I'm not quite sure why this would be especially suitable for application icons, though. Although Android on tablets, as well as some launchers (e.g. GEL), request an icon "one density higher" to show it bigger, this is supposed to be done using the regular mechanism (i.e.
drawable-xxxhdpi
, &c).It seems Google have updated their docs since all these answers, so hopefully this will help someone else in future :) Just came across this question myself, while creating a new (new new) project.
TL;DR: drawables may be stripped out as part of dp-specific resource optimisation. Mipmaps will not be stripped.
(from http://developer.android.com/tools/projects/index.html#mipmap)
There are two distinct uses of mipmaps:
For launcher icons when building density specific APKs. Some developers build separate APKs for every density, to keep the APK size down. However some launchers (shipped with some devices, or available on the Play Store) use larger icon sizes than the standard 48dp. Launchers use getDrawableForDensity and scale down if needed, rather than up, so the icons are high quality. For example on an hdpi tablet the launcher might load the xhdpi icon. By placing your launcher icon in the mipmap-xhdpi directory, it will not be stripped the way a drawable-xhdpi directory is when building an APK for hdpi devices. If you're building a single APK for all devices, then this doesn't really matter as the launcher can access the drawable resources for the desired density.
The actual mipmap API from 4.3. I haven't used this and am not familiar with it. It's not used by the Android Open Source Project launchers and I'm not aware of any other launcher using.
Here is my two cents in trying to explain the difference. There are two cases you deal with when working with images in Android:
You want to load an image for your device density and you are going to use it "as is", without changing its actual size. In this case you should work with drawables and Android will give you the best fitting image.
You want to load an image for your device density, but this image is going to be scaled up or down. For instance this is needed when you want to show a bigger launcher icon, or you have an animation, which increases image's size. In such cases, to ensure best image quality, you should put your image into mipmap folder. What Android will do is, it will try to pick up the image from a higher density bucket instead of scaling it up. This will increase sharpness (quality) of the image.
Thus, the rule of thumb to decide where to put your image into would be: