cocoa touch - Masking overlapping PNGs with each other in Objective C -

i have collection of uiimageviews, made pngs transparency.

i want able overlap these images on top of each other, show overlap, not entire image. image b placed on image a, want display image b image not transparent.

the uiimageviews move around.

so want use 1 png mask png, using objective c.

can done?

i don't know if ideal way accomplish this, using combination of masking , cropping.

so, example, check see if image transparent, if is, perform masking on 2 images. masking tutorial here

after you've masked images, perform cropping operation based on intersecting coordinates. check second answer here

in event that image not transparent, perform cropping operation without masking object. not sure if help, figure give start!