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Old 06-14-04, 12:29 PM   #1
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Join Date: Jun 2004
Posts: 4
Default nvidia driver calculates wrong Aspect Ratio

Dear all,

by using option "TwinView" together with option "TwinViewOrientation" "Below" I now managed to use my 1600x1200 15"-laptop-display together with my 1600x1200 external 20"-LCDisplay (which wasn´t possible one year ago on my laptop)! But the "nvidia" driver still has a tiny problem:

(II) NVIDIA(0): Virtual screen size determined to be 1600 x 2400
(**) NVIDIA(0): Display dimensions: (541, 406) mm
(WW) NVIDIA(0): Probed monitor is 200x310 mm, using Displaysize 541x406 mm
(**) NVIDIA(0): DPI set to (75, 150)

While the virtual screen size is determined correctly, and the size 541x406 (which I had to set manually using DisplaySize) is also correct for a single 20"-LCD, the "virtual" dimensions should be something like 541x812 giving a DPI of (75,75). The probed monitor has the correct aspect ratio, but it is much too small (giving too much dpi and thus e.g. too big fonts). The driver should also double the specified height, not only the detected (but too small) height of one of the two screens.

I am not allowed to correct this in the XF86Config using the line DisplaySize 541 812, because sometimes I use the laptop without the external screen (obviously these numbers would be wrong then).

As a bug fix, I thought to start the Xserver with the option -dpi 75. But on my SuSE 9.1 system a change of the following line
:0 local@tty1 /usr/X11R6/bin/X -nolisten tcp -br vt7
in the file /opt/kde3/share/config/kdm/Xservers is ignored. On the other hand, starting X from the console (/usr/X11R6/bin/X -dpi 75) makes XFree.0.log to report a successful change of the DPI:
(++) NVIDIA(0): DPI set to (75, 75)

One question:
- Where is the relevant SuSE file so that my change is not ignored any longer?

Three suggestions to NVidia:
- When is an Option "DPI" added to the list of XF86Config options?
- When does the nvidia driver calculate the virtual size of both screens correctly as it does now with the virtual resolution (simply adding both together according to the orientation, but take into account "clone")?
- And finally, does it make sense to have an additional DisplaySize option for the other LCD in TwinMode (something like "SecondDisplaySize")?

Thanks a lot for reading this and thinking a little bit about it (and maybe giving one or two answers).
hpt is offline   Reply With Quote
Old 07-17-04, 08:28 PM   #2
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Join Date: Jul 2004
Posts: 35
Default Re: nvidia driver calculates wrong Aspect Ratio

The bug is still there. Its effects range from mild irritation to total unusability of the system. Recommended steps to fix:

1. if DisplaySize is defined in Monitor section of XF86Config, assume that it defines the size of the primary monitor (not the entire TwinView desktop, like it currently does). Calculate different dimensions (or DPI) for X after each mode change, so that the DPI values in use are always that of the primary monitor, and that the display dimensions (of the TwinView desktop resolution) are totalTWDisplayWidth := displayWidth * desktopXSize / primaryMonitorXSize, and the same thing for height. This should get the DPI values correct for the primary screen.

2. if DisplaySize is not defined, assume 75x75 DPI (like X does), 96x96 DPI (possibly closer to actual value on modern systems) or whatever, as long as the pixels are square with that. Note that screen shape may change with different modes, but the pixels always are square. For example, 1920x1080 gives 1.78:1 mode here, but 1280x960 is 1.33:1, on the same monitor.

Thanks for awesome drivers! After getting my first NV card (FX5600) a couple of months ago, I quickly began getting rid of all the ATI hardware I had (was 100 % ATI at that time, except for one Matrox Millennium II in one of the servers). Now I have a couple of FX5900XT plus other NV cards and only my laptop has ATI now (and I hate it more and more every day, due to extremely bad drivers).

Keep up the good work!
Tronic is offline   Reply With Quote

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