[Bug 89416] UE4Editor crash after load project

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89416

--- Comment #7 from Jason Ekstrand <jason at jlekstrand.net> ---
(In reply to Matt Turner from comment #6)
> (In reply to Jason Ekstrand from comment #5)
> > (In reply to Uriy Zhuravlev from comment #4)
> > > Ok, alignment... maybe I can fix it.
> > 
> > Uriy,
> > The problem here is that the code originally assumed that the destination
> > would always be nicely aligned but the source may not.  When rgba8_copy
> > function started getting used for texture *download* via ReadPixels and
> > GetTexImage the assumption now fails and it is the source that is aligned
> > and not the destination.  To fix this we need to do one of two things. 
> > Either a) make the rgba8_copy function use unaligned reads (which would b
> > slower) or b) make two versions of the rgba8_copy function: one for upload
> > and one for download.
> 
> Basically, this all stems from the fact that there's no guarantee that the
> pointer given to glReadPixels/glGetTexImage is suitably aligned?
> 
> Do you have time to fix this before the release on Friday? Trying to figure
> if I need to work on this.

I think it would probably be more efficient if you did.  The above should be
enough of a brain dump on what needs to happen in the tiled_memcpy paths.  The
rest is writing suitable mmx code and you probably know more about that than I
do.  TBH: I'd probably be asking you on IRC what instructions to use anyway. 
If you don't want to bother with threading it through the tiled_memcpy code, I
can do that part quick enough.

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