What do I need for 30bpp? [solved...?]

[Ant P.]

Hi.

I've got a screen that can do 30bpp modes (Dell U2410), a graphics card that should support it (R700 Radeon) and a choice between DVI or HDMI. I'm currently using the DVI connection and starting X with -depth 30 gives an error that the Radeon driver doesn't support 30bpp. Should I give up now, or do I just need a different cable?

[NeddySeagoon]

Ant P.

30 is a very strange number for colour depth. Its usually 1,8,15,16,24 and 32.

The U2410 specification does say Colour Support: 1.07 billion colours, which is 30 bits.
You need a lot more than just a video driver to do 30 bit colour. Xorg and your applications need to support it too.

Xorg actually uses 32 bit colour internally. Thats 8 bits each for RGB and Alpha, which is the transparency.
This fits in quite nicely with the way CPUs work, in bytes, words and double words. 8, 16 and 32 bits.
The numbers in my opening sentence are not random - fit with CPU internal operations.

HDMI and DVI both support 30 bpp. In fact, definitions for 36 and 48 bpp are in place.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

[chithanh]

To my knowledge, the U2410 supports 30-bit color only through the DisplayPort input. But I could be wrong there.

To what extent the radeon driver supports 30-bit I don't know, you will have to ask the upstream developers (#radeon on irc.freenode.net or their mailing list xorg-driver-ati@lists.x.org).

[Ant P.]

[Ant P.]

Half a dozen years late, but it looks like I can finally play with this stuff.

Current system:
- Radeon RX550 — xf86-video-amdgpu 18.0.1, kernel 4.15.12 (I believe xf86-video-radeon can also do 30bpp now too)
- xorg-server 1.19.99.901-r1, run with -depth 30 on the command line
- 2011 Dell U2410 on DVI, 2017 LG Ultra HD on DisplayPort

Results:
- GTK2 and Qt5 work fine, so does x11-terms/st, so that's 90% of my apps covered.
- GTK3 visually works fine.
- Firefox (GTK3) lags like hell, painful to even type this. It seems like it's software-rendering which is terrible for a hidpi screen.
- Electron-based apps seem to render garbage colours unless I convince them to use OpenGL rendering.
- Openbox renders the titlebar backgrounds and icons far too dark. The text is normal, oddly enough.
- The rest of my desktop pieces (tint2, compton {in both glx and xrender mode}, hsetroot) seem to have no problem.
- Had to uninstall SLiM as it crashes on startup. Doesn't faze me, I'm just running Xorg directly from runit now.
- Java (icedtea8) AWT dies with a Java-sized error explicitly saying it doesn't do 30bpp. No playing minecraft for a while…
- UT2004 gets killed at startup by the GCC SSP mechanism, which is kinda sad to see after it's survived the rest of the world changing from under it since my first Gentoo install. Any chance there's a FOSS engine project for it out there somewhere?
- Odamex draws only a black screen. These two use libsdl:1.2 (which I remember used to get horribly confused by compositing too), so maybe fixing that would fix them?
- other games I've tried seem to be fine
- Krita still sucks at gradients and refuses to draw one without visible banding (given a 32bpc-float colourspace). GIMP does too. Bah.
- MPV renders garbage, OBS segfaults. Maybe not ready for desktop use just yet...

[Ant P.]

Some more findings:

mpv --vo=vdpau was rendering garbage, but mpv --vo=opengl --hwdec=vdpau looks fine. I was using the former because amdgpu has broken page flip behaviour with the latter though, so I'll have to figure out a different workaround for that.

The firefox slowness was due to it deciding, behind my back, to disable all hardware acceleration for no reason.

Vulkan stuff just flat out crashes at startup, not that it was very safe previously.

Java works, albeit with some screen corruption, if I do this:

[Ant P.]

I've gone ahead and wrote this up in a slightly more coherent format on the wiki. If anyone else is in a position to do so, give it a try and see what breaks.

[q3cpma]

Hello, any updates about this? I'm about to pull the trigger on a nice Coloredge screen and want to know if some stuff got fixed in the meantime.

[Ant P.]

Not much to add, but I haven't had the urge to try again. Maybe I'll do another attempt.
The AMD drivers all work. I believe Nvidia was scared into adding 30bpp allowance to their non-Quadro cards shortly after Mesa got it.

imlib2-based software has problems, but imlib2 seems like abandonware in general and 30bpp isn't the only thing it struggles with.
libsdl1 still seems to be a problem, but upstream has been talking about preserving old games by writing a shim that proxies API calls to libsdl2. That might solve itself sooner or later.

[q3cpma]

Well, I don't need libsdl1, fortunately. imlib2 is required by sxiv and I use a patched sxiv as manga reader, so I'll need to migrate everything to imv, which might be painful; by the way, imlib2-1.6.0 was release a month ago, so it's not really abandonware. Did you bother writing a bug report on https://phab.enlightenment.org/ ?

I was more concerned about Vulkan outright not working, though.

[Delicates]

Stock nVIDIA drivers have worked fine for many years with X.Org via DisplayPort managing DCI 4k resolution at 30bpp.
The software is what's been taking a while to catch up.
I just tried it again now, and there seems to be a lot of improvement, but still a lot left for it to be usable.

What works:
* Qt5 seems to handle it now (previously it couldn't)
* LibreOffice works OK (was unusable before)
* VLC seems to work fine, even playing UHD videos full screen.
* Firefox and Thunderbird are "usable".
* Edit: Oracle Java works with the "opengl" trick mentioned above.

What's still broken:
* Firefox and Thunderbird are extremely slow/laggy - YouTube videos play at about 3 FPS regardless of selected resolution - This is probably the biggest showstopper.
* Windows title-bars are messed up in KDE - this is surprising considering the overall Qt5 improvement, and the rest of the GUI being fine.
* Oracle Java 1.8 throws an Unsupported bit depth exception. Edit: the "opengl" trick mentioned above works!
* Oracle Java 11.0.2 runs, but shows blank app window - perhaps the app needs to be recompiled. Edit: the "opengl" trick mentioned above works!
* GIMP seems to show images fine, but the interface is a bit messed up.
* Wine apps seem to be hit and miss, some apps run fine, some crash (e.g. notepad).

[Ztt3]

Fixed the 30bpp related bugs I found in imlib2 when using feh:
https://phab.enlightenment.org/T8799
https://phab.enlightenment.org/T8808
Feel free to test if the patches help with your imlib2 problems.