[MPlayer-dev-eng] Re: [MPlayer-users] ssa reader for mplayer using vf_overlay

[Robert Henney]

On Sat, Oct 01, 2005 at 10:08:05AM -0400, Jason Tackaberry wrote:
> On Sat, 2005-10-01 at 03:35 -0400, Robert Henney wrote:
> > 	UPDATE: did some further testing before sending this mail and
> > 	came up with a pattern.  if the y value passed with the
> > 	invalidate command is ODD, then this strange color shift
> > 	always happens, but never when it's EVEN.
> 
> Ah, yes, this does make sense. :)  I'll add some code to vf_overlay
> which internally aligns the coordinates given to multiples of 2.  I can
> reproduce the problem here.

in the meantime I'm just accounting for that in my code by clearing the 
least significant bit of the y value I pass, and things are looking
good.

> >     // 'mem' is pointer to overlay memory
> [...]
> > 	pW = (unsigned long*)mem + 4 + imagex + (y+imagey) * screenwidth;
> 
> The BGRA buffer is offset 16 bytes from the shmem address, so it looks
> like you should be adding 16, rather than 4.

that's half the purpose of that cast there.  longs on my system are 4
bytes, so since the cast takes precedence then any integer value applied
to it will affect the pointer in multples of 4 bytes.  :)

the way I did it above though is not portable, and I should replace
it with this:

(unsigned long*)mem + 16/(sizeof long) + imagex ...


> Cheers,
> Jason.

-- 
robh