drmModeSetCrtc and how to use x,y

[Rian Quinn]

With respect to Windows XDDM, in the past I was able to map more than one
display to a single framebuffer by leveraging width, height, stride, and
then adding an offset to the framebuffer's char*. I can see how this would
work with dumb buffers as they are basically a simple linear ARGB buffer,
but how does this work with respect to GBM buffers that are tiled?

My initial thought was to use the x,y in drmModeSetCrtc. Basically, I could
create a framebuffer in GBM that spanned multiple displays. From there, I
could use drmModeSetCrtc to tell the CRTC where, within the framebuffer, to
get it's data. Is that the proper use of x,y in drmModeSetCrtc, and if so,
does it handle the titling issues behind the scenes?

Also, are there any limitations with a design like that. For example, is it
possible to create GBM buffers that span 6 monitors wide?

Thanks,
- Rian
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