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[bug?] jit.gl.node and alpha color message

August 26, 2013 | 6:37 am

Hi,

I have to send a color message, changing the alpha value, to a videoplane object.
Alpha does not seem to be linear via a jit.gl.node object.
It’s ok whithout using node.

I don’t understand why…. is it a bug ?

here is the patch (MBP retina, OS 10.8.4, Max 6.1.3) :

– Pasted Max Patch, click to expand. –

thanks


August 29, 2013 | 1:17 am

Nobody Knows ? …. the Trouble I’ve Seen… with alpha & nodes…..


August 29, 2013 | 2:14 am

i can notice the same here (osx10.6.8 max6.1.3), unfortunately i’m not too familiar with jitter nodes, so i can’t really help, but mayyybe it’s related to the default erase color of videoplane/node ? or some blending thing ?


September 2, 2013 | 12:01 pm

it looks like when you capture the first videoplane to the gl.node, it effectively premultiplies the alpha value into the texture, while still keeping the alpha channel. when you display on the second videoplane with @blend_enable 1, it applies the alpha channel to the already premultiplied texture, thereby giving your non-linear effect.

solution is to set @blend_enable 0 on second videoplane.


September 3, 2013 | 7:56 pm

Hi,
Thanks for your reply.

@Rob : yes, it look like an alpha premultiplies problem….
you solution is not good for me, i need to use alpha on second videoplane.

In fact, i try to use 32 gl.cornerpins routed to 8 sub-masters gl.nodes, routed to 2 masters gl.nodes, routed to the gl.render…. and i need to use alpha…
So in my case, the gl.nodes premultiplies twice the alpha value !
May be using nodes isn’t the right way ?


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