Double GrabPass

Unity Engine
1

Hi, I’m working on something a bit tricky (for me at least) and I was wondering if it was possible to make multiple GrabPass pass on a single shader.

To explain a litlle, I have 3 meshes on my scene, one in the foreground (Dude), one in the background (Sky) and one in the middle (Glass).

they are rendered in this order : the Dude, then the Sky and then Wall. Eveymesh is Opaque. ( I’ve set an order on the render queue)
My shader is applied to the mesh Glass
Here what I want to do with them: http://dl.dropbox.com/u/24855439/GlassSkyDude.jpg

I want to make a GrabPass with only my Dude on it, and to redisplay it on the Glass first and
I want to make a GrabPass with only my Sky on it, and to redisplay it on the Glass too. The reason I want it separated is that my Dude is gonna make a lot a movement and I want it inverted so it’s not possible to mix it with the sky because the sky is pretty static (except the wind movement).

Given the order that my mesh are drawn now, I can only make a grabPass with the Sky and the Dude.

So here are my questions : Is it possible to make too GrabPass on a single Shader and If it’s possible, is there any tricks to GrabSomehting but ignore a mesh (for exemple my dude or my sky)???

Thanks!

2

Hi b4cksp4ce,

Im not quite following what you are trying to do, but you can do every technical aspect of what you have asked.

you can treat the grabpass as you would any other pass. The trick being it will do the grab just before the pass following it.
The grabpass also grabs the alpha channel data of whats previously been written. So if you write masking data to the alpha channel you can use that to work around objects you dont want to effect that were drawn earlier than the grab.

Cheers
brn

3

As far as I have understood, you can make a grabPass in the previous shader for example and use the grabbed texture in the next one without redoing a GrabPass! If I’m right about what I’ve understood, that’s really good news. I’ll try that. Thanks!