Problems with monitor calibration and MergedFB/TwinView

Graeme Gill graeme2 at
Sat Aug 12 21:18:44 PDT 2006

A number of my users are reporting problems with color management
and multiple monitors when running their under NVidia TwinView, or MergedFB.

Screen calibration works for standard X11 multiscreen because both
normal X11 protocol requests, and XFree86-VidModeExtension Video LUT
access can be directed at any particular screen.

When Xinerama is running, things also work fine, because while
Xinerama makes it look like there is only a single screen
as far as normal X11 graphic operations are concerned, it
provides an extension to report the actual number of underlying
screens, and extensions like XFree86-VidModeExtension aren't
affected by Xinerama, and continue to allow access to the
individual screens Video LUTs. An assumption has to be made
that the Xinerama screen number corresponds to the
XFree86-VidModeExtension screen number.

Can anybody describe how NVidia TwinView and MergeFB work, or
point to relevant documentation that covers how applications
can discover how many underlying screens there are when either of
these multi-monitor modes are running, and how this interacts with
accessing the individual screens Video LUTs using the
XFree86-VidModeExtension ?

If it's not possible to access individual screens Video LUTs when
running TwinView/MergeFB using XFree86-VidModeExtension, is there
an alternate extension available to allow this, or if there isn't,
is there some way of the client detecting that TwinView/MergeFB
is running, and at least more elegantly reporting that color
management is not supported in such configurations ?

Is there an email contact at NVidia and at ATI who I can discuss
these issues with ?

Also, can anyone point to some documentation that defines the
XFree86-VidModeExtension functions supported by each
major & minor XFree86-VidModeExtension version ?

	Graeme Gill.

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