Changing the starting point of the X draw

Luc Verhaegen libv at
Mon Apr 3 05:44:37 PDT 2006

On Mon, Apr 03, 2006 at 08:02:31AM -0300, Colin Nickerson wrote:
> Hi everyone.
> I have recently started work on a DIY projector.  I have made a mistake and
> have lost the signal to 1/8 of my screen (128 pixels to the far left).  I
> can still get a 800x600 projector out of it though.
> Is it possible to modify the X codebase to start drawing at, lets say,
> location (128,0) to (128+res_w, 0+res_h).  If this is possible, where should
> I start looking?  I'm not sure if this would be usefull for anyone else, but
> if I get it working I would also like to submit a patch for this.
> Thanks,
> Colin

You're probably talking about poking with modelines here. You can for 
instance, take a gtf generated 1024x600

Modeline "1024x600_60.00"  48.96  1024 1064 1168 1312  600 601 604 622  -HSync +Vsync

Then adjust the horizontal active video:
Modeline "800x600_60.00"  48.96  800 1064 1168 1312  600 601 604 622  -HSync +Vsync

Then move the H sync forward:
Modeline "800x600_60.00"  48.96  800 840 944 1312  600 601 604 622  -HSync +Vsync

You should now have 800x600 shifted to the right. Feel free to move both 
HSyncStart and HSyncEnd up in increments of 8 until you get the desired 

YMMV though, as not all drivers nor all hardware combinations support 

Luc Verhaegen.

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