• Maxon Cinema 4D

  Transparent mask for particles

  Posted by Bjorn Van oostrum on February 6, 2009 at 1:04 pm

  Hi All,

  I need a little help with the following:

  I want particles to move around a transparent object within a scene. In a way that they will be visible when they’re in front of it, and dissapear behind an object, spline (mask) or whatever. As long as I won’t see the masking object itself…

  I’ve already tried to boolean the extruded spline from the particles but this ended up in a much too heavy scene.

  Hope someone can help!

  thanks in advance,

  bjorn

  Adam Trachtenberg replied 17 years, 5 months ago 2 Members · 5 Replies
• 5 Replies

• 

  Adam Trachtenberg

  February 6, 2009 at 4:50 pm

  You could do it by compositing, but that would require two render passes. Here’s a trick:

  In your invisible/masking object’s transparency channel, add a tiny bit of refraction (1.001 or something like that).

  Then put a compositing tag on your emitter (standard particles) or particle geometry object (TP).

  Drag the invisible/masking object into the compositing tag’s exclusion tab and tick on the refraction icon (the arrow that bends as it passes through the plane).

  That should do what you want. The only downside is that you’ll probably need to enable Best AA because anything that is visible behind the refracting object won’t receive geometry AA.
• 

  Bjorn Van oostrum

  February 9, 2009 at 10:28 am

  Hi Adam,

  Could you please explain what you mean with “ticking the refraction icon” and where I can find it.

  thanks
• 

  Adam Trachtenberg

  February 9, 2009 at 3:28 pm

  [Bjorn van Oostrum] “Could you please explain what you mean with “ticking the refraction icon” and where I can find it.”

  Now that you ask it’s occurred to me that you don’t have to use refraction at all — simple transparency will do. The settings are in the compositing tag’s Exclusion tab:

  

  I’m referring to the icons to the right of the word “Disc,” above. The first (highlighted one) is transparency, then refraction, then reflection, then heirarchy.

  In this case the compositing tag is on a cube that’s partially obscured by a disc, which has a transparent material on it. By excluding the disc and transparency, the cube won’t be seen through transparent portions of the disc.

  If I had ticked the reflection icon then the cube also wouldn’t show up as a reflection on the disc, etc.
• 

  Bjorn Van oostrum

  February 9, 2009 at 4:25 pm

  Thanks again Adam, it works brilliant but…

  I only seem to be able to do this in a new and empty scene without my global illuminated objects. When using a sky and GI the objects will become visible…
  Any suggestions?
• 

  Adam Trachtenberg

  February 9, 2009 at 6:24 pm

  That’s odd. Turning on GI and using a sky object makes no difference here. What Cinema version are you using? Can you post a scene where it’s not working?

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