garageCube

dear all,

it seems like an easy task, but i just can't find how to do it...

how can i use a image (i.e. square) as a "keyhole" mask, so that the image below the shape is seen just where the square is? and the rest is masked and invisible?

of course i can create black PNGs with a hole. but on resizing and rotation the border will show and i whould need huuuuge images to aviod that.

so i would like to have the option to "invert" the alpha on a PNG. can this be done??

thanks a lot!