Question

My app consists of a round ball whose radius I have specified as 35 pixels in the code. The user muse prevent the ball from colliding with other balls.

I have drawn an 800 px by 800 px vector graphic with 72 ppi resolution that I want to use as the bitmap for this image.

What sizes do I scale the image to for the drawable-ldpi, -mdpi and -hdpi folders so that the bitmap is the same size on all devices and also so that the collision detection works fine ? i.e. The app calculates the ball to be 35 pixels but the screen shows a smaller or larger image so the collisions will be all wrong and the user won’t know what’s going on.

I really don’t know much about this so any help will be hugely appreciated.

Answer 1

From the android developer guide:

To create alternative bitmap drawables for different densities, you
should follow the 3:4:6:8 scaling ratio between the four generalized
densities. For example, if you have a bitmap drawable that’s 48×48
pixels for medium-density screen (the size for a launcher icon), all
the different sizes should be:

36x36 for low-density
48x48 for medium-density
72x72 for high-density
96x96 for extra high-density

Also, one of the best practices for supporting multiple screen resolutions is: “Do not use hard-coded pixel values in your application code”.

Since your applications deals with pixel values at runtime, you might want to read the section Additional Density Considerations and below that section.