Ah…I never played this game and seeing mockup gives me better picture what you need.
My idea was :
1. you pick point on screen
2. pressing widget zooms whole screen and centers to this point
3. pressing widget again returns it back to normal state
This is easy, because I already did these function and I can re-use them
Harder way, but maybe better for you could be to improve zoom widget. In this case…(like Alex said) you can make selection on the screen. This selection can be copied to widget’s background in each screen update.
For this I must find more time