LibDRM Cloned Monitor Support

[Rob Clark]

On Tue, Nov 11, 2014 at 12:19 PM, Rian Quinn <rianquinn at gmail.com> wrote:
> What exactly is the correct way to support cloned monitors using LibDRM. As
> I see it, there are two methods:
>
> - Use the connector array in drmModeSetCrtc
> - Use one crtc per connector, but share the same framebuffer.
>
> Right now I am using option #2 as it seems to be the most flexible, but my
> current issue is that on laptops, the connector for the laptop's main screen
> is only retuning 1 mode (tested on a Lenovo, and an HP folio), which means
> that your unlikely to find a common mode between the laptop monitor, and an
> external screen (monitor or projector).

#2 is the method that will work on all hw..  usually DE's will pick
the closest matching modes between the two connectors/outputs, and
truncate edges on the smaller display (via non-zero x/y offset).  Some
hw may support upscaling to fit, although that isn't really exposed in
a completely standard way at the moment.

BR,
-R

> So with the above problem, right now the only thing that I know to do would
> be to set the resolution of the laptop monitor and external monitor to be
> their "preferred" resolution, and then copy and scale for "cloned mode"
> which seems like a terrible idea considering the laptop monitor should be
> able to set itself to some more basic resolutions (like 800x600).
>
> - Rian
>
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