Mental Ray clipping planes issue

[Dave Buckley]

I'm trying to render a scene using clipping planes and mental ray.

 

At first there was an issue and it just wouldn't clip. However if I then enabled 'Scanline' under my rendering algorithms of the renderer tab, it decided to take the clips into account.

 

does anybody know why this happens?

[Macer]

I've had issues in the past too, never got to the bottom of it though! Light portals caused problems too, but that was several years ago now. I can't say that I've used clipping planes since then...

 

From the help file:

WARNING If you use the mental ray renderer on page 7165, geometry outside the

clipping planes might still appear in renderings.

[Dave Buckley]

yeh it's the first time i've had to use them in a while too.

 

like i say I fixed it by turning on enabling scanline in my rendering algorithms rollout. i was just intrigued as to why iw worked this way. all working though which is a good thing

[odouble]

I believe the clipping plane in 3ds max (when using Mentalray) is based on the scanline algorithm; it does not work with raytracing the first bounce. It basically uses the the near and far bounds used to optimize scanline rendering to clip your scene.

The Mentalray scanline algorithm does not sort objects in a bsp tree like the raytracing algorithm. It sorts objects by using a direct line of sight from the cameras perspective (kinda like zDepth). It is this ability that allows the clipping plane to work with scanline and not raytracing as far as I know.