[PD] GEM - alpha blending of images over movies

Roman Haefeli reduzierer at yahoo.de
Fri Feb 16 21:52:57 CET 2007

On Sat, 2007-02-17 at 06:32 +1100, Item State wrote:
> unfortunately i have the same problem with your patch
> (psychedelic colours). the [colorRGB] is pretty cool,
> it does exactly what i want, but this only works here
> with [pix_texture] but have no effect when using
> [pix_draw] instead...

i hope i can clarify this a bit in my own (maybe not too correct) words.
there are actually two different domains in Gem: opengl and 'pix'es. all
opengl-based stuff is renderend on the gpu (graphic card's cpu), whereas
all pixel-based objects are calculated on the cpu. playing and
processing videos and pictures happens in the pix-domain (afaik, all
pix_*-objects work in that domain). pix_texture is used to convert an
image (from a picture or a video) to a texture, that can be applied to a
vertex . that means the picture is then in the opengl-domain and cannot
be processed with pix_*-objects anymore. so there are actually two (or
more?) ways  of alpha-blending a picture:
1) do everything in the pix-domain and use [pix_alpha] (i'm not quite
sure anymore about that)
2) give it to the opengl-domain using [pix_texture] and use the fourth
(alpha-channel-)inlet of [colorRGB].
the latter approach has the advantage, that everything is rendered on
gpu, which saves you a lot of cpu-power. whenever you can, i would do
stuff in the opengl-domain (unless you don't have any 3d-acceleration

i hope i didn't tell you something completely wrong (please someone
correct me, if i did)


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