[mythtv] Re: [mythtv-commits] Bob and XVMC

[Ivor Hewitt]

On Friday 04 Feb 2005 23:55, Daniel Thor Kristjansson wrote:
> On Fri, 4 Feb 2005, Ivor Hewitt wrote:
> ]Yup indeed fixes XvMC. Green flickering all over screen with just XV.
>
> Are you getting the flickering in XV with the current CVS as of this
> afternoon?
>
Hi Daniel,

Yup XV still flickering and I can't work out what's going on. I can remove the 
mad green flashing by removing the memcpy's in PrepareFrame for GUID_YV12.. 
but I don't understand what that's supposed to be doing... 

Then with that removed the behaviour is that the first field is displayed 
fine, but the second field is displayed with inverted colours. Hence some 
rather strange flickering effects. I thought it was just a memory alignment 
problem, but it doesnt appear to be.... I guess it's a bug somewhere in the 
unichrome driver.

> ]Out of interest what is the halfLineSrc adjustment supposed to be doing
> for ]XvMC? I thought the field 1 and 2 values were what told the XvMC
> driver which ]field was active. So why does the image need offsetting?
>
> No idea why it's need, I think the driver should take care of it. It may
> be just an nvidia driver bug. But XvMC standard is not clear on who
> should do the offsetting, so doing or not doing the offsetting may both
> be proper for the driver writer.

In that case I don't understand the bob logic for the PutImage calls. The 
adjustments to the y position affect the destination position not the source. 
The logic appears to only make sense where dest resolution is the same as the 
source resolution, I can't see how it could/would work otherwise....

For example say the source fields are vertically interleaved frames A and B:-
ABABAB

which is scaled (badly) to the destination say to:-
ABBABBAB

Offsetting the destination will result in alternating between:

ABBABBAB and
 ABBABBAB

Which will look orrible. Surely just the source position needs offsetting to 
produce alternating:-

ABBABBAB and
BAABAABA

Regards,
Ivor.