Custom Shader Node With Transparency

[garion-mail]

Hi all,

I have written my own shading node that reads a texture and does some basic lighting (OpenGL Blinn style). Now I want to extend the node to use the alpha channel of the texture as transparency. However I can not find any information on how to do this.

I have compared my setup in the hypergraph with a default lambert shading node in Maya using a texture with alpha channel. This one works the way I want with the transparency. But all it does is that it reads the alpha channel from the texture, but the output is still an outColor of RGB. So where is the transparency out encoded?

Is it so that the lambert shading node perhaps reads the color already in the frame buffer and does manual blending based on texture alpha? Is this how one handles transparency in shading nodes in Maya? If so, how do I access the previous color?

Any help very much appreciated.

Thanks!

[joojaa]

Well hyper graph only represents what happens to software rendered objects. Or any object that has a procedural texture in between. The shading node is handed over a fll texture map an if thats only thing thats connected maya uses it.

Since your making ashader your free to do as you please.

[garion-mail]

Hi Joojaa,

I am not sure I follow. Given that I connect the file transparency to my shading node, how do I get Maya to use it as transparency?

Basically, what is the lambert shading node doing with the transparency it gets from the file? If all the shading node outputs is RGB (outColor) connected to the xSG.surfaceShader, then how do maya know if the particular fragment is opaque or not?

What is the piece I am missing?

Thanks a lot!

[garion-mail]

I solved it by creating an output attribute like this:
outTransparency = nAttr.createColor( "outTransparency", "ot" );

Seems to be another hard coded attribute. Wonder where all these are listed?

[joojaa]

All the inputs that are here in nodes that compute something that never get connected just magically do something are such hidden inputs. Look in the node reference, it is even more important in figuing maya api stuff than actually reading the api reference thats jut 1/3 of everything there is.

Just a quick list of stuff.

pointCamera
pointObj
pointWorld
normalCamera
uvCoord
rayDirection
tangentUCamera
tangentVCamera
matrixEyeToWorld
pixelCenter
flippedNormal
...

the list goes on and on and on.