Re: xsrc/59952: xsetwallpaper: server/client endian mismatch

["Michael van Elst via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR xsrc/59952; it has been noted by GNATS.

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: xsrc/59952: xsetwallpaper: server/client endian mismatch
Date: Wed, 4 Feb 2026 06:57:11 -0000 (UTC)

 gnats-admin%NetBSD.org@localhost ("Adrian Chadd via gnats") writes:
 
 > Well, my next diff is handling servers that aren't ARGB. :-P
 > 
 > I'm tempted to lean in here and not bswap at all but let x11 do it. I
 > believe that's what the API is meant to encourage.
 
 
 XCreateImage() gets you an XImage suited for the display and visual.
 You then create the pixel data in the appropriate format and
 XPutImage() transfers it to the server.
 
 XInitImage() lets you create an XImage yourself for the format you
 specify. If the characteristics of the image (for example, byte_order
 and bitmap_unit) differ from what the server requires, XPutImage()
 makes the necessary conversions.
 
 XImage contains pointers to pixel manipulation functions (that
 XInitImage will initialize). So you should not modify the XImage
 structure yourself after it is initialized or created by some
 Xlib function.
 
 The pixel depth is nothing that could be converted automatically,
 operations with different depths always fail with a BadMatch.
 
 You can render a XYBitmap to a deeper display because the XYBitmap
 is seen as pixels in background (0-bits) and foreground (1-bits)
 color. So there is no depth conversion taking place between pixel
 values.
 
 Saying that, automatic conversions was never popular. Any conversion
 is slow, especially when done with single pixel operations. The code
 I've seen that relied on this was usually handling small pre-rendered
 images in a user interface (like button imagery). Everything else would
 convert the data once when loading or generating an image and not
 every time when it gets rendered for refreshing a window. Something
 like xsetwallpaper probably doesn't care, as rendering is done only once.