[PD] some GEM questions ...

oliver oliver at klingt.org
Wed Apr 12 20:20:32 CEST 2017

hi, dear list !

i'm looking for an insight into some questions i ran into recently when 
i decided to give GEM a serious shot after all.
please be patient, i'm probably spoiled by JITTER ...

PD 0.47.1
GEM 0.93.3
WINDOWS 7/64bit

1.) is there a way to do image processing (i.e. levels, contrast, 
satturation etc.) on the GPU ?

as far as i understood [pix_...] objects do all their processing with 
the CPU
and others like [color] do it in openGL (thus GPU), is that right ?
now, for big textures (1280x720 or bigger) that would be the preferable 
way of manipulating things, right ?

2.) i'm looking for objects that do "compositing", i.e. ways to overlay 
two pix sources. apart from the ones existing (add, multiplay, subtract, 
mix) , i would love to have the well-known (AE,vegas, etc.) compositing 
modes like "darken", "lighten", "dodge" "difference" etc. - but also 
chromakeying !

is this possible ? and is it possible to do in opengl rather than with a 
[pix_] object ?

3.) concerning shaders:
documentation here is quite sparse and no GLSL example patch works on my 

the PD window says just this:

[glsl_vertex]: error reading file
[glsl_fragment]: error reading file

is my graphics card not up to it ?

4.) are there any GEM GLSL shaders collections around ? i didn't really 
find anything useful. again i am basically searching for compositing 
shaders (like the ones that VADE made for Jitter some years ago) and 
something like brightness, contrast, saturation etc.)

thanks for any hints and helps !



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