What is the difference between XYPixmap, ZPixmap, XImage, XShmImage and Bitmap in X?

Question

The only fact I know is that XImage is stored on the client side and the pixmaps are stored on the server side. Is it so simple?

Then what is XY and Z Pixmaps and why X needs so many types of image formats?

Why there is no XY and Z Images?

And what is Bitmap in the context of Xlib and why there is a function XCreateBitmapFromData that returns Pixmap handle? (or pointer? or structure?)

Trigeminal

Answer 1

From the X11 protocol specification:

The data for a pixmap is said to be in XY format if it is organized as a set of bitmaps representing individual bit planes, with the planes appearing from most-significant to least-significant in bit order.

Which means for an RGB image you have all the red channel data followed by the green and then blue instead of the more traditional RGB triplets (ZPixmap).

Hackler

Not very clear (as all X11 documentations) and in addition does not looks trustworthy. Maybe some detailed description will be better. For example, why the planes must contain R, G and B bytes? Maybe they are bit planes and the first plane contains only the first bit of every pixel, the second - second and so on? – Trigeminal

Yeah, it's not majorly clear but I think that's a description of how you'd probably use an XY format pixmap in real life. The more practical answer is "this is not the image format you are looking for". – Hackler