Creating Nine (9) Patch png files with Gradients

问题

I want to create a nine patch button background with a gradient for my android app. I was wondering how gradients work. I would think that the os would have to figure out how to apply the gradient as the button stretched and I'm guessing that information (a graphic vector equation) is not available in the 9 patch file? So is there a solution for this problem? Also, what about dithering, etc. I have created a few nine-patch button backgrounds, but none of them have a gradient. yet. Thanks in advance.

回答1:

Why do you want to use a 9-patch for that? 9-patches stretch an area of an image by copying/duplicating pixels. That will not work well with gradients. Have you considered using a GradientDrawable instead?

<shape android:shape="rectangle">
    <gradient android:startColor="..." android:endColor="..." />
</shape>

See shape drawables.

回答2:

As to your question about dithering, I didn't address that with my previous reply.

You'll have to enable dithering from your application code I'm afraid, as far as I know there is no way to do it from XML. You can use the setDither(true) call on your drawable, as documented here.

This will make for much nicer gradients, since it mitigates the banding artifacts you see on gradient images. I haven't tried this on shape drawables though, just PNG files.

Also, if you're targeting Gingerbread it may be worth reading Bitmap quality, banding and dithering. Apparently they snuck a change into 2.3 which addresses these issues.

来源：https://stackoverflow.com/questions/5140749/creating-nine-9-patch-png-files-with-gradients