Pixmap data. This is abstracted in the sense that the code here does not care what the data points to (hence the void). The module using this data should know whether it is these point to png data or image data of whatever form. The module is not required to use all these fields - as png data includes transparancy, it will generally not use the mask fields and instead just put its data into the appropriate image fields.
As images can now be of variable size (and potentially re-sized), the size information is stored here.
Definition in file image.h.