Re: [patch] add "underwave" face attribute

[Aurélien Aptel]

Time for some updates.

I've fixed most of the bugs related to X11/Windows but I think I'll
have to change the approach to underwave.

Drawing chunk of waves (when width of the underwave < width of one
wave) often ends up with (little) artifacts due to rounding problem.
To have a perfect wave no matter the position or size I should clip
the region of the underwave and only draw full waves, letting the
clipping do the work.

On X11, I know how to change the clipping region but I don't know how
to restore it. The clipping region is stored in the GC but it *can't*
be requested with XGetGCValues() [1]. I could just remove the clipping
region altogether when I'm done it but I'm pretty sure this will have
some side effects. I've asked about it on stackoverflow[2] but I
haven't got any satisfying answer yet.

On Windows, I've looked at the GDI documentation[3] (which is what
w32term.c currently use) on MSDN and it looks doable.

On Mac OSX, I still don't know if my patch compile/works (could
someone please report back?). I haven't looked at the clipping stuff
either. I was hoping someone who actually knows what he's doing in
Objective C/COCOA could help me.

1: http://tronche.com/gui/x/xlib/GC/XGetGCValues.html
2: 
http://stackoverflow.com/questions/9037676/how-can-i-limit-the-surface-in-which-xlib-graphics-primitives-draw
3: http://msdn.microsoft.com/en-us/library/dd145203%28v=vs.85%29.aspx