android live wallpaper rescaling

Question

I am learning how to make live wallpapers, but I have a dilemma I'm sure all who start off have as well.

There is so many resolution screen sizes, how can I just make one set of artwork to be rescaled in code for all versions? I know it's been done as I seen the images in the apk's on a lot of them and they get rescaled.

If it was just one image that did not need any positioning that would be easy, but my problem is I have to get the background image rescaled to fit all devices, I also have animations that fit in a certain x and y position on that background image to fit in place so it looks like the whole background is being animated but only parts of it is (my way of staying away from 300 images of frame by frame live wallpapers).

So the background image needs to be rescaled and the animations need to be rescaled as well to the exact percentage as the background image and they need to sit in a specific x and y position.

Any help would be appreciated so I can get this going.

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I tired a few things, figured I would make a scaler for everything example: int scaler; then in onSurfaceChanged scaler = width /1024; //if the bigger image is 1024. that will give me a ratio to work with everywhere. then scale accordingly using scaleBitmap by multiplying the scaler by the image height and width, and also use the same scaler for positioning example image x lets say is at 50, scale it using the same thing x = scaler * 50; that should take care of scaling and positioning, just how to translate all this into java is the next lesson, since I'm new to java, I used to program for flash and php but this is a lot different, take some getting used to. Next thing is how to pan the width, when you move your screen from side to side how to make the image show is the next puzzle I have figure out. Right now it just shows the same width no matter what even though the width is double what the surface shows. If you got an answer or somewhere I can find out the info on this one that would be greatly appreciated.

Answer 1

Well, um, all I can say is "Welcome to the real world." You get your screen dimensions passed to you via onSurfaceChanged, and yes, it is your job to figure out how to scale everything based on this data. That's why they pay us the big bucks. :-) You will want to make sure your resources are large enough to fit the biggest display you intend to support, so you will always be shrinking things (which distorts much less than expanding things).

Suggest starting with "best practices for screen independence" here: http://developer.android.com/guide/practices/screens_support.html

Additional comments in re your request for more help...

1. You cannot (necessarily) scale your artwork just using the width, because you need to support multiple aspect ratios. If the screen proportions do not match your artwork, you must decide if you want to distort your artwork, leave blank spaces, etc.
2. I'm not sure how to interpret your trouble passing around the screen dimensions. Most of us put all of our active code within a single engine class, so our methods can share data via private variables. For example, in the Cube wallpaper in the SDK, onSurfaceChanged() sets mCenterX for later use in drawCube(). I suggest beginning with a similar, simple approach.
3. Handling scrolling takes some "intelligence" and a careful assessment of the data you receive via onOffsetsChanged(). xStep indicates how many screens your launcher supports. Normally xStep will be 0.25, indicating 5 screens (i.e. xOffset = 0, 0.25, 0.5, 0.75, or 1) but it can be any value from 0 to 1; 0.5 would indicate 3 screens. xPixels gives you an indication of how much the launcher "wants" you to shift your imagery based on the screen you're on; normally you should respect this. On my phone, the launcher "desires" a virtual wallpaper with twice the pixels of the physical screen, so each scroll is supposed to shift things only one quarter of one screen's pixels. All this, and more, is documented in http://developer.android.com/reference/android/app/WallpaperManager.html This is not "easy" coding--apps are easier than wallpaper. :-)

Good luck...George

P.S. I'll throw in one more thing: somewhere along the line you might want to retrieve the "desired minimum width" of the wallpaper desired by the launcher, so you can explicitly understand the virtualization implicit in xPixels. For example, in my engine constructor, I have

mContext = getApplicationContext();
mWM = WallpaperManager.getInstance(mContext);
mDW = mWM.getDesiredMinimumWidth();

My device has 320 pixel width; I get mDW = 640; as I scroll from screen to screen, xPixels changes by 80 each time...because four scrolls (across five screens) is supposed to double the amount of revealed artwork (this effect is called "parallax scrolling"). The rightmost section has xPixels equals 0; the center (of five) sections has xPixels = -160, etc.