Applying mask using Stencil Function

[goro]

Hello Friends!
I am using Stencil Function to apply and remove the masked portion of an object. before applying the mask my objects are looking like this:
http://i438.photobucket.com/albums/qq105/gaurav_kudalkar/Clipping1.jpg

The front object is logo2, the back object is logo1 & in between object is named masked & it'll be used for masking.
Simple code for viewing this in your vizard is:
import viz
viz.go()

piazza = viz.addChild('piazza.osgb')

logo1 = viz.addChild('logo.ive')
logo1.setPosition(0.3,1,5)

logo2 = viz.addChild('logo.ive')
logo2.setPosition(-0.3,1,3)


mask = viz.addChild('logo.ive')
mask.setPosition(0,1,4)

Now when we apply stencil function with using following code:

import viz
viz.setOption('viz.display.stencil',1)
viz.go()

#Clear stencil buffer every frame
viz.MainWindow.setClearMask(viz.GL_STENCIL_BUFFER_ BIT,viz.MASK_ADD)

piazza = viz.addChild('piazza.osgb')

logo1 = viz.addChild('logo.ive')
logo1.setPosition(0.3,1,5)

logo2 = viz.addChild('logo.ive')
logo2.setPosition(-0.3,1,3)


mask = viz.addChild('logo.ive')
mask.setPosition(0,1,4)

mask.stencilFunc(viz.StencilFunc.RenderMask())
mask.disable([viz.COLOR_WRITE,viz.DEPTH_WRITE])
mask.enable(viz.CULL_FACE)

mask.drawOrder(-1)

logo1.stencilFunc(viz.StencilFunc.RenderOutsideMas k())
logo1.clipPlane([0,0,1,-2])
logo2.stencilFunc(viz.StencilFunc.RenderOutsideMas k())
logo2.clipPlane([0,0,1,-2])


We get an output as shown below:
http://i438.photobucket.com/albums/qq105/gaurav_kudalkar/Clipping2.jpg

Now here you'll notice that both the front and back objects are affected by mask. What we want is only back object should get affected and not the front one. But the function will be applied on both the objects as they keep on rotating in our application so many times the front object will go back side of the mask and that time the mask has to clip that object.

Wondering if there is any function viz.StencilFunc.RenderBacksideMask() or viz.StencilFunc.RenderBehindMask()!

Can you please suggest me where am I going wrong?
Is there any way to do this by using shaders?

[goro]

No need to use stencil function. We just have to use mask.disable(viz.COLOR_WRITE) this command will not display the object but it'll still write to depth. So the object behind this invisible object will get affected. Don't forget to set mask.drawOrder(-1).

Code:
import viz
viz.setOption('viz.display.stencil',1)
viz.go()

piazza = viz.addChild('piazza.osgb')

logo1 = viz.addChild('logo.ive')
logo1.setPosition(0.3,1,5)

logo2 = viz.addChild('logo.ive')
logo2.setPosition(-0.3,1,3)

mask = viz.addChild('logo.ive')
mask.setPosition(0,1,4)

mask.disable(viz.COLOR_WRITE)
mask.drawOrder(-1)

http://i438.photobucket.com/albums/qq105/gaurav_kudalkar/Clipping3.jpg

Now don't worry about the black mask. if you set the environment scene i.e. piazza draw order lower than mask draw order then piazza will get rendered before mask.

add this line to the previous code
piazza.drawOrder(-2)

and you'll get the desired output
http://i438.photobucket.com/albums/qq105/gaurav_kudalkar/Clipping4.jpg