Scroll encoder works incorrectly if the speed is <100%

[GUAN-Xihao]

Describe the bug
Part of the rendering area has not been updated while scrolling. (I can reproduce it on other software, but firefox is the most commonly used one.)

To Reproduce
Steps to reproduce the behavior:

1. xpra start :zz -d video
2. xpra attach ssh://xx:yy/zz
3. Currently, the speed should be Fixed Speed: Auto, Minimum Speed: 1% (default settings from GUI)
4. Open a Firefox (129.0.2), and then scroll up and scroll down the page very fast use mouse wheel.
5. The following is the incorrect rendering.
   
   And we found this is H264.

2024-12-13 15:22:35,097 video_encode('auto', XShmImageWrapper(BGRX: 0, 0, 1095, 554), typedict({'quality': 70, 'speed': 80, 'rgb_formats': ('YUV420P', 'YUV422P', 'YUV444P', 'NV12', 'GBRP', 'BGRX', 'RGBX', 'RGB', 'BGR'), 'lz4': True, 'alpha': False, 'av-delay': 0, 'window-size': (1095, 554), 'damage-time': 1560201.408667398, 'process-damage-time': 1560201.446648618, 'depth': 24})) image size: 1095x554 , encoder/csc size: 1094x554
2024-12-13 15:22:35,098 video_encode x264 encoder: h264 1094x554  result is     165 bytes,   682 MPixels/s, client options={'frame': 2, 'pts': 1163, 'csc': 'YUV420P', 'full-range': True}

6. No error was found around the operation logs. (note: with -d video)
7. The following combination is tested, all quality settings are auto.
   a . Encoding: Auto, Fixed Speed Auto, Result: incorrect. (effected encoder: H264)
   b . Encoding: H264, Fixed Speed Auto, Result: incorrect.
   b1. Encoding: H264, Fixed Speed Lowest Lentency (100%), Result: Looks good.
   b2. Encoding: H264, Fixed Speed Lowest Bandwidth (1%); Average (50%), Low lentency(70%) ( Result: Incorrect.
   c . Encoding: JPEG, Fixed Speed Auto, Result: Looks good.
   c2. Encoding: JPEG, Fixed Speed Lowest Bandwidth (1%), Result: Looks good.
   d . Encoding: VP8, Fixed Speed Auto, Result: Looks good.
   d2. Encoding: VP8, Fixed Speed Lowest Bandwidth (1%), Result: Looks good.

System Information (please complete the following information):

• Server OS: RockyLinux 8
• Client OS: Windows 11 with Intel 12th Gen iGPU only.
• Xpra Server Version 6.2.2
• Xpra Client Version 6.2.2 (Full build)

Additional context

1. NVENC is disabled on the server side.
2. It seems like I can reproduce it since at least 6.1.x. (To be double confirmed)
3. Not tested on NVGPU (TBD)'
4. It looks like if the window of Firefox is larger, it is easier to trigger the behaviour. (Most time I maximize Firefox to test)
5. The incorrect rendering will auto-recover while moving the mouse over the page and wiggling it a couple of times.

[totaam]

@GUAN-Xihao can you reproduce with / without opengl enabled? (--opengl=no|force)

This sounds like what 775d435 was meant to fix?
Do you have any desktop scaling enabled?
Can you change the scaling settings?

[GUAN-Xihao]

Retested with the following options:

1. Disconnect multiple monitors, only use one. Change the Windows Scale (HiDPI setting) to 100%, and sign off the PC, then relogin.
2. Run the following commands to verify if it is related to opengl or desktop scaling.

Xpra_cmd.exe attach ssh:// -d video --opengl=force --encoding=h264 --speed=1
Xpra_cmd.exe attach ssh:// -d video --opengl=no --encoding=h264 --speed=1
Xpra_cmd.exe attach ssh:// -d video --opengl=no --encoding=h264 --speed=1 --desktop-scaling=off
Xpra_cmd.exe attach ssh:// -d video --opengl=force --encoding=h264 --speed=1 --desktop-scaling=off

Result: all can reproduce the issue. This issue can not be workaround by opengl options or desktop scaling.

[totaam]

Please try --encodings=no-scroll.

[GUAN-Xihao]

Please try --encodings=no-scroll.

Yep, you've got it. All the following looks good. --encodings=no-scroll is the workaround.

Xpra_cmd.exe attach ssh:// -d video --opengl=force --encoding=h264 --speed=1 --encodings=no-scroll
Xpra_cmd.exe attach ssh:// -d video --opengl=no --encoding=h264 --speed=1 --encodings=no-scroll
Xpra_cmd.exe attach ssh:// -d video --opengl=no --encoding=h264 --speed=1 --desktop-scaling=off --encodings=no-scroll
Xpra_cmd.exe attach ssh:// -d video --opengl=force --encoding=h264 --speed=1 --desktop-scaling=off --encodings=no-scroll

[totaam]

FYI: as per the docs, you should never need to set --encoding=.
Use speed and quality instead.

[GUAN-Xihao]

FYI: as per the docs, you should never need to set --encoding=. Use speed and quality instead.

Got it, I just want to make sure it is H264 encoding. It would be equivalent if I set it via GUI Picture -> Encoding -> H.264, am I correct?

BTW, I tried the following is working well.

-d video --opengl=force --speed=1 --encodings=no-scroll

[totaam]

Got it, I just want to make sure it is H264 encoding.

Best to leave it to the xpra server, it usually knows best.

[GUAN-Xihao]

Got it, I just want to make sure it is H264 encoding.

Best to leave it to the xpra server, it usually knows best.

Thanks for clarifying it. Xpra server will choose the best encoding and mix using multiple encoding.
The reason why I try to force using H264 is due to test for this issue. It can only reproduce on H264 encoding (includes auto encoding if server uses H264). So, forcing H264 is for testing purposes.

Normal daily usage I will leave it as auto. (Maybe --no-scroll as for now?)

[totaam]

Makes sense!

[GUAN-Xihao]

Makes sense!

Hi totaam, I have edited the title from H264 to scroll. It should beklongs to the scroll encoding issue.