From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Richter Subject: Re: 3.16, i915: less colors in X? Date: Sun, 22 Jun 2014 00:51:55 +0200 Message-ID: <53A60C8B.3090106@rus.uni-stuttgart.de> References: <20140621202901.GA3840@amd.pavel.ucw.cz> <7569_1403385738_53A5F78A_7569_14810_1_2527490.06bevSLs0l@merkaba> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from hydra.rus.uni-stuttgart.de (hydra.rus.uni-stuttgart.de [129.69.192.3]) by gabe.freedesktop.org (Postfix) with ESMTP id CA79A6E388 for ; Sat, 21 Jun 2014 15:52:03 -0700 (PDT) In-Reply-To: <7569_1403385738_53A5F78A_7569_14810_1_2527490.06bevSLs0l@merkaba> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: intel-gfx@lists.freedesktop.org, Martin@lichtvoll.de List-Id: intel-gfx@lists.freedesktop.org Hi Martin, >> I'm trying to figure out how to ask X what color depth it is using...? > > I think: > > martin@merkaba:~> xdpyinfo | grep -i "depth of root" > depth of root window: 24 planes > > but am not completely sure. > >> This is thinkpad x60 with Debian 6.0.9. AFAIK the 830GM chipset does not offer any support for hardware dithering. Whether the panel in the x60 does I do not know, though. However, what is remarkable is that graphics on a 16 bit(!) screen may look more pleasing than graphics on a 24 bit screen, at least for such ancient machines. The reason is that the panel cuts the bitdepth down from 8 to 6 bits, without any dithering, just by cutting off the LSBs. However, if you select a 16bpp mode to begin with, some desktop environments (specifically gnome) apply a dithering of their own, even though the output is only 5 bit per component. This is at least what I see here on the IBM R31 and the Fujitsu S6010: Gnome desktop at 16bpp looks better than the desktop at 8bpp, due to the lack of hardware dithering. The X11 intel driver had an option "Dac6Bit" to signal the 6 bit panel resolution to X (even though the display pipeline operates in 8 bit mode), but I have never seen this working in the past time. It seems not to be supported anymore. Probably that's the culprit. Martin, you should probably test Ville's alm_fixes5 kernel branch, its support for the 830GM chipset of the X30 is in my experience much better than that of the drm-intel-nightly or official kernels. Greetings, Thomas