New KDE(4) looks bad on our X-terminals

[dksayers]

We use X-terminal hardware to connect to a Linux server running kubuntu 7.10 and all is fine. When I upgrade to any kubuntu with the new kde (4) we seem to have issues. The main problem is shading and colors. It seems that with most of our X-Terminals where there should be clean shading there are either black or white dots to compensate for the shading. We do have one terminal that displays the screen cleanly. Doing an xdpyinfo and comparing shows there are some differences between the 2 types of different terminals.

Good Terminal:
=============
vendor string: The X.Org Foundation
X.Org version: 6.8.99.903


Bad Terminal:
============
vendor string: The XFree86 Project, Inc
XFree86 version: 4.3.0.1
Missing X extensions:
DPMS
MIT-SHM
RENDER
XFIXES
XFree86-Misc
XFree86-VidModeExtension
XInputExtension
XKEYBOARD
XTEST


To demonstrate the problem I ran up a System settings window and took a screen shot of the window from both the good and bad terminals. One can see the results at:

http:www.cis.net.au/kde/kde.html

Is there any way of configuring or de-tuning kde so it will work on these X-Termials. I would prefer to stay with KDE even though I have proven that these issues do not occur with ubuntu 9.04 (gnome).

[dksayers]

Re: New KDE(4) looks bad on our X-terminals

OPPS, sorry the URL didnt work due to typeo. Hope this one works.

http://www.cis.net.au/kde/kde.html

[Teunis]

Re: New KDE(4) looks bad on our X-terminals

It's many years ago I last had the wrangle screen settings but I notice the screen #0 depths differences.

32 bit is what I see on the 'good' screen, the pixelated one seems to dither emulate (thanks ChrisLilley!) with less available bits.

[ChrisLilley]

Re: New KDE(4) looks bad on our X-terminals

The bad result is because of dithering.
http://en.wikipedia.org/wiki/Dither

The dithering is caused by the use of a 16 bit visual instead of a 24 or 32 bit one, so it has only 32 levels of each of red, green, and blue. Other values are simulated with a dot pattern, (which looks like crap).

screen #0:
 dimensions:  1280x1024 pixels (325x260 millimeters)
 resolution:  100x100 dots per inch
 depths (2):  1, 16
 root window id:  0x25
 depth of root window:  16 planes

The 'good' terminal on the other hand has

screen #0:
 dimensions:  1280x1024 pixels (342x271 millimeters)
 resolution:  95x96 dots per inch
 depths (7):  16, 1, 4, 8, 15, 24, 32
 root window id:  0x49
 depth of root window:  16 planes
 number of colormaps:  minimum 1, maximum 1

So although the root window is 16 bits, the X server can create windows at other depths (24, 32) on request. Presumably the linux server is requesting 24 or 32 bits, which gives you the correct looking result.

(It might be that background images are dithered, even on the good terminal, due to the root window being only 16 bits.)

Its not clear why you didn't get dithering with Kubuntu 7.10; perhaps it supported 16 bit visuals directly (which would give banding, but not dithering) while perhaps KDE4, if it can't find a 24 or 32 bit visual, automatically dithers to 256 colours or something horrid like that.

[dksayers]

Re: New KDE(4) looks bad on our X-terminals

Many thanks for the prod in the right direction. I thought I would try lowering the resolution on the bad X-Terminals and the problem still exists. The reason I thought this would help was with less resolution there would be more (video) memory for higher color. This has indeed done what I thought and an xdpyinfo now shows 24 bit color. This however has not fixed the 'dithering' issue.
The new xdypinfo snippet looks like:

screen #0:
 dimensions:  1024x768 pixels (260x195 millimeters)
 resolution:  100x100 dots per inch
 depths (2):  1, 24
 root window id:  0x25
 depth of root window:  24 planes
 number of colormaps:  minimum 1, maximum 1
 default colormap:  0x22
 default number of colormap cells:  256
 preallocated pixels:  black 0, white 16777215
 options:  backing-store NO, save-unders NO
 largest cursor:  1024x768

As Chris suggested, this does not fully explain why the problem does not occur in Kubuntu 7.10 or ubuntu 9.04 (gnome).

[flarson]

Re: New KDE(4) looks bad on our X-terminals

One difference I noticed was that the "bad" display had openGL support. Could it be that it is trying to use anti-aliasing or something that it is picking up from the server, which it didn't get in the earlier version?