[PD] pix_video alphachannel

[IOhannes m zmoelnig]

cdriko at free.fr wrote:
> hello
> 
> I've seen your message on the pd list about alpha mix of live input
> 
> I'had got the same problem as you with the pix_mix box (vertical flip)

well, this is basically a problem of how the images are presented to Gem
by whichever source. some systems prefer to anchor an image at the
upper-right corner, others (like openGL) prefer to assume that (0/0) is
in the lower-right corner.
this makes images from one system appear upside down in the other.

luckily, Gem automatically takes care of this when it comes to texturing
(so you normally shouldn't notice).

however, when you want to combine 2 such sources, Gem uses the raw data
(for performance reasons), and ignores if one of the 2 images is flipped
upside down.

thats why you get weird effects in such cases.

how to cope with this:
1) don't use pix_objects for doing things you can do without (e.g. mixing)
2) recode the combining pix_objects to obey the upside down flags
3) flip on of the images via the [pix_flip] object

> 
> It seems that gem prefers working in 3D than with pix_ objects ...

obivously, since this is what Gem is made for.
you can get a lot of performance from this.

> 
> 
> so
> I've made this box to mix two sources
> (the mix is in 3D however, it's not
> recordable with pix_record, but it's viewable)
> 

it _is_ recordable via [pix_record]; use [pix_snap].


mfg.asdr
IOhannes