Android: Maintaining image resource size

I know there are tons of questions on this topic, but I tried searching through tons of "android dpi" posts and read the online documentation but haven't found the exact question that I have.

If I want to create a button (or any image resource) that will take up the same space on the screen on all devices - how do I do that?

I understand that there are specific screen sizes and dpi's that Android looks at etc. but I don't quite understand how big a specific image should be to look right on any screen.

Say that I have the followi开发者_JS百科ng setup for my drawable and layout folders (Application is only landscape):

res/drawable-ldpi/button.png (120 dpi)
res/drawable-mdpi/button.png (160 dpi)
res/drawable-hdpi/button.png (240 dpi)

res/layout-small/main.xml - button is set to 100dp
res/layout-normal/main.xml - button is set to 100dp
res/layout-large/main.xml - button is set to 100dp

Say I have a button that I want to be 100dp on any screen. Following the 3:4:6 scale ratio rule it seems that if I have a button resource that's 100px wide for the mdpi density I should make another button for the ldpi density that's 75px, and one for the hdpi density that's 150px. Is that correct? Do I create the 75px button at 120dpi, the 100px button at 160dpi and the 150px button at 240dpi and then just say android:layout_width="100dp" in all three layout files? Or do I make all three buttons 100px at the different dpi's?

Now what if I have that button 9 patched. Do I have to create the button three times at 120dpi, 160dpi and 240dpi all of which are 100px in size? Or do I just create one 9 patched button at 100px and 160dpi and place it in the mdpi drawable folder?

The online documentation is a bit confusing for me so I'm looking for a simplified answer.

This is for Android versions 1.6+ (Not the new stuff for 3.2 etc)

Thanks for your help ... I just want a button to take up the same space on a 3.7" screen as a 7" screen and not be blurry!

Did you sort this? Afaik, and from my experience, don't change the dpi when creating the images in say, Photoshop. I always left mine at standard which is 72 I think. Regardless, I don't think it matters if you set it to a million.

The px values you mentioned are correct for l m and h. I would leave the mdpi qualifier off the folder name though; I'm unsure of the protocol if on an xhdpi device there is no drawable folder with no xhdpi qualifier and no folder without qualifiers.

Workflow: Create your images at 75, 100 and 150. Put 75 in ldpi folder, 100 in drawables folder with no qualifier, and 150 in hdpi. Leave your layouts as they are now, with the 100dp. They should scale correctly. That said, I don't think you need to specify the image size if you're using the full resolution.

Comments to address inaccuracies in my answer are always welcome, even years down the line.