[PD] RE : Re: need help with gem and glsl feedback

Py Fave pyfave at gmail.com
Sun Oct 6 22:13:14 CEST 2013

Hello , i just opened your last patch and am looking at it .
weanwhile i reply to your points

2013/10/6 Jack <jack at rybn.org>:
> Hello,
> Le 05/10/2013 22:51, Py Fave a écrit :
> in fact my problem is not solved .
> it seems like the feedback effect  happens everywhere but on the
> surface drawn by the shader .
> According to the patch, the feedback is applied on a [square 4] (where there
> is also the [torus 2]).
> Then, [gemframebuffer] 'snap' the whole 'inside' [square 4]. And your torus
> is inside this snapshot (as texels and not vertices).

yes ,and then there is  some feedback on the texels of the square .
but in my patch if i rotate the torus i get some feedback but not on the
shaded part (only the silhouette of the torus .  i don't know why .
i would like everything to go in the feedback loop .

in fact i try to have trails that show "geodesics" on a surface
later i plan to replace my torus with other models .

> i use a torus , in perspective wich has a shader applied .
> i tried the following workaround(archive is joined ) , but still no luck .
> the file to open has a OPEN in name .
> It seems there is no circle4.geom, [receive13] and [nshader0]
> objects/abstractions in your .zip.

sorry i forgot  .

receive13 only is missing .
it's part of ext13 library (and is in pd-extended iirc)

[receive13 nothing ]could  be replaced by receive nShader1
or all the shader abstraction can be replaced by the classical shader network
with fragment shader = circle4.frag  and vertex shader = circle4.vert.
no .geom was used

> i would like the dots to have the feedback ,
> or dots + geometry alltogether.
> I can't see dot in your patch (or gem window), maybe they come from geometry
> shader (which is missing) ?
i didn't use geometry shader . just  fragment .
glsl program complains in the abstraction  but no harm here i think

> i tried pix_snap2tex ( using gems.feedback from pdmtl abstractions) too
> but no luck because we can't choose the mixing function .
> and i would like only white to make trails .
> and i don't know how to keep the supporting geometry from appearing .
> the torus should be full black with a white trail only .
> A simple possibility is to use 2 torus, a black 'on' a white. And use the
> white for the trail ?
> An other way :
> white torus as texture
> |__> in the feedback __> output feedback as texture
> |__> convert white in black texel __> output black torus as texture
> Then mix (multiply) black torus with white feedback to get a black torus
> with white trails.
> ++
> Jack
i'll send a modified patch a bit later .

Thank you so much i see some good things from the last patch you sent .

it is not what i want to do but opens other directions
and perhaps i was focusing on one method but there seems to be alternatives .

i'll update this thread tomorrow .
i have to keep some life away from computer :-)

Thanks for your help


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