I'm trying to create a cover for my magazine that has a chalk board with writing on. I want the user to be able to erase the writing with their finger but can't figure out how to do it. All i can do is draw a solid colour over the top. What i want is for the finger swipe to erase the .png image instead. wondered if it can be done using a mask but I can only get a mask to reveal solid colour not an image.