I am about to port an application to OSX from win32. I need to do very simple but very high quality perspective warps on bitmaps. Before I get stuck into learning it is OpenGL the right API to use? Can you get it to interpolate every pixel in a large source bitmap?
The first advantage you get is with openGL your graphics code will be with a common graphics API for both machines.
Then any future changes in the graphics routines will not require a total rewrite as if you used native direct X, and then converted it to native OS-X code.