X11 - XCreateImage, Visual * vis parameter

Question

I'm working with X11 and I've been looking for the reason why, in every program I've seen trying to create an image with XCreateImage, the parameter vis is set to "CopyFromParent".

I've already see this question in stackoverflow.

But the examples also use the same value. ¿Could anyone explain me the reason? Thank you

Answer 1

It's one of Xlib's classes which says "copy the Visual class Type from the parent". Visual Type being "DirectColor", "PsuedoColor", "red_mask", "green_mask", "blue_mask", etc.

http://tronche.com/gui/x/xlib/window/visual-types.html#Visual

CopyFromParent is a flag saying "copy these values from the, typically the main display window - XOpenDisplay(NULL).