Questions about possible EXA Composite acceleration for savage

Alex Deucher alexdeucher at
Mon Apr 14 12:08:23 PDT 2008

On Mon, Apr 14, 2008 at 2:56 PM, Alex Villací­s Lasso
<a_villacis at> wrote:
> I am currently studying the feasibility of implementing Composite
>  acceleration for the savage driver. The 3D hardware available has two
>  texture units, which require power-of-two dimensions to work (both width
>  and height). From what I could see, setting the POT flag only sets up a
>  POT source pitch, but does nothing for the height. What could happen if
>  I use the next bigger power-of-two height as the texture height? Does
>  EXA guarantee that I will not overrun into the next stored texture, or not?
>  Another question: apparently the POT flag has effect on the reported
>  texture pitch, not on the actual image width
>  (PixmapPtr->drawable->width). What is stored on the right of the true
>  width? Is it garbage, or does EXA guarantee it to be some constant
>  value, or that it will always be covered by the mask texture or source
>  alpha channel? How should this be handled if the driver needs to repeat
>  the source texture, as apparently required by a source texture of 1x1
>  and a destination coordinate of, say 28, 15? Note that, even though 1 is
>  a power of two, EXA still honors the pitch alignment of 128 bytes (one
>  tile pitch).
>  This might be easier to answer for me if I could examine existing source
>  code for some other driver that has both EXA Composite acceleration and
>  the POT requirement. Do you know whether any of the existing drivers
>  meet both requirements?

the kdrive ati driver supports composite on r128 which only supports
POT textures:
KAA is very similar to EXA.


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