Normally a pixmap has its own memory buffer to store pixels, attached to the header information that describes the width, height, pitch etc.
An alternative is that you have this header information pointing to some other pre-existing block of memory, that is associated with some other pixmap. So the two pixmap headers sort of share the same pixmap pixels. Then using that `window within a pixmap`, you can just deal with what is within that window, like a clipped window, and ignore what's outside of it.
An alternative is that you have this header information pointing to some other pre-existing block of memory, that is associated with some other pixmap. So the two pixmap headers sort of share the same pixmap pixels. Then using that `window within a pixmap`, you can just deal with what is within that window, like a clipped window, and ignore what's outside of it.