Updated EXA docs

Eric Anholt eta at lclark.edu
Sun Aug 7 10:16:07 PDT 2005

On Sun, 2005-08-07 at 09:33 -0700, Jesse Barnes wrote:
> I've updated the EXA documentation I wrote at 
> http://www.virtuousgeek.org/exa-driver.txt to include a better 
> description of the offscreen pitch and alignment fields (thanks Michael 
> and Adam!).  Please mail me if there's anything more you'd like to see.

I would nitpick it a bit:
"depends on your screen's pitch alignment constraints" ->
"should use the X value from the adjusted width based on virtualX, after
accounting for the accelerator's pitch alignment constraints."

In "every access to the framebuffer..." that sounds like it would cover
CPU accesses to the framebuffer, which doesn't make sense and isn't
true.  Instead, "Alignment settings for pixmaps, to allow for hardware
acceleration from and to them.  Not applied to all pixmaps -- the
visible screen is an exception, and thus Prepare* acceleration hooks
should test for these and fail appropriately."  offscreenByteAlign is
the value that the pixmap's offset from beginning of framebuffer must be
aligned to.  offscreenPitch is the value that the pitch of a pixmap must
be aligned to (also ALIGN_POT applies).

Stride is another name for pitch -- the offset from the beginning of one
line of the pixmap to the next)

In the xvideo bit about sizing, I would s/must/should/ -- I don't think
it's required, but I don't know.

Eric Anholt                                     eta at lclark.edu
http://people.freebsd.org/~anholt/              anholt at FreeBSD.org

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