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What do I need for 30bpp? [solved...?]
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Ant P.
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PostPosted: Sat Nov 17, 2012 7:17 pm    Post subject: What do I need for 30bpp? [solved...?] Reply with quote

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?


Last edited by Ant P. on Mon Apr 16, 2018 3:35 pm; edited 1 time in total
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NeddySeagoon
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PostPosted: Sat Nov 17, 2012 8:03 pm    Post subject: Reply with quote

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.
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chithanh
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PostPosted: Sat Nov 17, 2012 8:06 pm    Post subject: Reply with quote

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).
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Ant P.
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PostPosted: Sat Nov 17, 2012 10:49 pm    Post subject: Reply with quote

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

This seems to be the case, from what I've been reading. I've got an AMD E450 attached via DP, but I don't use that as a desktop and my main PC only has the other two.

I'll forget about it for now, I only started looking because someone in another thread was having problems with 30bpp on nvidia-drivers... wanted to see if I could reproduce the bug :)
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Ant P.
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PostPosted: Mon Apr 16, 2018 3:34 pm    Post subject: Reply with quote

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...
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Ant P.
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PostPosted: Thu Apr 19, 2018 3:23 pm    Post subject: Reply with quote

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:
Code:
export _JAVA_OPTIONS='-Dsun.java2d.opengl=true'


I've tried other libsdl1.2 things and found the same black screen problem with them, so if nothing else at least it's fixable in one place.
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Ant P.
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PostPosted: Fri Apr 20, 2018 9:48 pm    Post subject: Reply with quote

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.
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