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Old 12-05-09, 06:47 AM   #1
kleptophobiac
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Default Artifically limiting usable resolution in X or WM to compensate for overscan?

I have a CRT HDTV that I'm feeding via a DVI->HDMI cable. The video is crisp and good, the colors are accurate, and the vertical refresh syncing works. Hurray.

The only problem is that my display overscans like nobody's business, and I can't see about 100px on either side and about 40px on the top and bottom. That means all of my navigational content is where I can't see it. Scroll bars, menu bars, nav bars, control icons, blah blah blah. It's pretty miserable.

I don't really care to try and do anything fancy. I don't need 1:1 pixel mapping - this is an analog screen, it just doesn't matter. I don't need to get my full resolution - 1920x1080 is already way more than I need for basic media playback and internet browsing.

Is there an easy way to have an effective resolution below that represented by the display mode? Effectively the goal is to just ignore the existence of all of the pixels outside of a predefined window.

I've done a lot of google searching and found that there are fairly extremely in-depth solutions involving custom modelines and ignoring EDID values. These seem like they're aimed at people who are really trying to be accurate about this business and get exactly placement and 1:1 mapping. I just don't care. Surely there's a simpler way. Does anybody know what that is? My vague feeling is that this is something that should be taken care of either at the X level or the window manager level, but certainly not the application level.

Any help is very much appreciated!
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Old 12-05-09, 07:35 AM   #2
thefirstm
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Default Re: Artifically limiting usable resolution in X or WM to compensate for overscan?

There is an Overscan setting in nvidia-settings, at least if you use a (very) recent driver version...
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Old 12-05-09, 12:44 PM   #3
kleptophobiac
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Default Re: Artifically limiting usable resolution in X or WM to compensate for overscan?

Quote:
Originally Posted by thefirstm View Post
There is an Overscan setting in nvidia-settings, at least if you use a (very) recent driver version...
Is that active for all output connections, and work to reduce (and not just increase) overscan? If so, that really is a new and very exciting feature. I know that it exists for svideo output, but that's been there for ages.

I'll check up on that immediately, thanks.

EDIT:
Seems that I'm running the latest 190.42 drivers, but there's no overscan control for DVI output. Any thoughts on another means to crop the usable screen area?

Thanks!
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Old 12-05-09, 01:26 PM   #4
AaronP
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Default Re: Artifically limiting usable resolution in X or WM to compensate for overscan?

You can try configuring your display for a smaller resolution using nvidia-settings, and then going into the properties page for the display, enabling "Force Full GPU Scaling", and setting the scaling method to "Centered".
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Old 12-05-09, 03:33 PM   #5
kleptophobiac
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Default Re: Artifically limiting usable resolution in X or WM to compensate for overscan?

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Originally Posted by AaronP View Post
You can try configuring your display for a smaller resolution using nvidia-settings, and then going into the properties page for the display, enabling "Force Full GPU Scaling", and setting the scaling method to "Centered".
Huh, I never noticed that option before. It seems to work pretty well when I have an LCD connected to DVI, but when it's the CRT television it doesn't seem to do anything. I'll bet the TV does some scaling as well.

I spent some time biting the bullet and just taking the custom modeline approach. It worked out quite well, though it took some time. For anyone who is curious, I started with the standard 1280x720 modeline that matched the pixel clock reported by EDID on my television, and then increased the front and back porch while decreasing the resolution by a corresponding amount. Thus both the horizontal and vertical scan time remained constant, but the resolution got smaller.

Now my display is perfectly sized and centered. In case anybody has a 37" Toshiba HF85 television and is trying to use linux with DVI... the modeline is:

Modeline "1160x672" 74.25 1160 1334 1374 1650 672 696 701 750 +hsync +vsync

But I'm guessing nobody else in the world has this combination.

Thanks guys!
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