Bug 5753 - Gradients show banding with rdesktop
Summary: Gradients show banding with rdesktop
Status: CLOSED FIXED
Alias: None
Product: ThinLinc
Classification: Unclassified
Component: | rdesktop (deprecated) (show other bugs)
Version: trunk
Hardware: PC Unknown
: P2 Normal
Target Milestone: 4.9.0
Assignee: Henrik Andersson
URL:
Keywords: derfian_tester, relnotes
Depends on:
Blocks:
 
Reported: 2015-12-15 13:07 CET by Karl Mikaelsson
Modified: 2018-02-27 09:59 CET (History)
2 users (show)

See Also:
Acceptance Criteria:


Attachments
Sample gradient with banding from WordPad (108.65 KB, image/png)
2015-12-15 13:07 CET, Karl Mikaelsson
Details

Description Karl Mikaelsson cendio 2015-12-15 13:07:36 CET
Created attachment 661 [details]
Sample gradient with banding from WordPad

Windows 2012 R2, CentOS 7 x86_64, ThinLinc-4.5.0post-4970

How to reproduce:

 - Connect to Windows server with tl-run-rdesktop.
 - Start WordPad.
 - Zoom out until you see the background gradient on each side of the empty document.

The gradient should be smooth, but it's showing clear banding, which would indicate a bit depth problem. The attached image shows the problem clearly. This warning from rdesktop is most likely the problem:

> WARNING: Remote desktop does not support colour depth 24; falling back to 16

Pierre mentioned something about Windows moving to 32-bit color instead of 24.
Comment 1 Karl Mikaelsson cendio 2017-10-18 12:57:22 CEST
https://github.com/rdesktop/rdesktop/pull/177
Comment 3 Karl Mikaelsson cendio 2017-12-12 18:44:22 CET
Vendor drop r32951 introduces support for 32-bit color.
Comment 4 Samuel Mannehed cendio 2017-12-29 14:28:12 CET
I can't reproduce the original problem with rdesktop from 4.5.0, 4.7.0 and 4.8.0 (and obviously not 4.8.0post). Connecting to the Windows Server 2012 lab environment.
Comment 5 Karl Mikaelsson cendio 2018-01-12 14:20:53 CET
(In reply to comment #4)
> I can't reproduce the original problem with rdesktop from 4.5.0, 4.7.0 and
> 4.8.0 (and obviously not 4.8.0post). Connecting to the Windows Server 2012 lab
> environment.

As in the server supports 24-bit color? I believe this bug report was based on the assumption that a server could support 32-bit but not 24-bit color. I believe that this could very well be a bad assumption though.
Comment 6 Karl Mikaelsson cendio 2018-01-15 14:15:20 CET
To some extent, this problem is still unsolved and probably unsolvable. Running "rdesktop -a 16 ..." will still give you banding artifacts in gradients. We need to control the server side to be able to introduce dithering or other techniques to combat the banding.
Comment 7 Karl Mikaelsson cendio 2018-01-30 09:42:53 CET
I just got this message when connecting to our Windows 2012R2 cluster:

> Remote desktop does not support colour depth 24; falling back to 32

So it appears that there ARE systems that support 32- but not 24-bit color. This means that we're not falling back to 16-bit color if there are better alternatives present. The banding still occurs at 16-bit but that's acceptable.

I haven't yet seen any problems with running 32-bit colors so the color conversion routines seem to work as expected. I'm considering this bug tested.
Comment 8 Karl Mikaelsson cendio 2018-02-23 10:05:51 CET
Forgot release notes.

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