View Full Version : render time polygon occlusion

11 November 2002, 06:11 PM
Hi all...

Ok, this is one of my greater LW gripes. Suppose I have a scene with several objects/layers, some of which are hidded by others. Now, when I render, no matter what I do, it always renders -everything-, including the hidden stuff (which of course eventually gets hidden). This can be a HUGE waste of render time.

The most recent example, I was doing a render with SkyTracer and most of the frame was covered with stuff, yet still I had to wait for ~15min for the entire backdrop to render.

Is there something I'm missing? Is there a way to save all this wasted time?

Thanks in advance.


11 November 2002, 06:23 PM
Yeap! I have the same problem since i hit F9 first time - I was staring at the render preview and wondered: "Why is he (LW :D ) rendering this box?? Ball stands in front of it so it won't be visible!!"

Can somebody answer this question??


11 November 2002, 06:40 PM
Did u guys have double sided surfaces?
Or little dissolve assigned for objects ?

11 November 2002, 06:46 PM
negative, and negative.

Besides, my problem is not that it's rendering the back+inside side of the top-most object, but objects that are clearly hidden. It renders them, and then renders the objects in front. Output is correct, the process is as inefficient as hell.


11 November 2002, 07:32 PM
Just make duplicates of those items and kill(k) the polys you dont want to render.

11 November 2002, 07:46 PM
1) There has GOT to be a way to fix this. I mean, I suddenly find myself fighting the urge to turn this into another "LW is great et all, but I can't believe that..." thread. I am taking a leap of faith here, and I'm assuming that it is somehow -my- fault. Something I should, or should not, have done, somehow...

2) You can't do that if you're doing animation. As soon as the camera angle and/or object orientation shifts, the missing faces will show. Besides, that suggestion re-defines the expression "going the long way around"...

3) And to re-clarify, example : I have a box and a sphere. From the camera's POV, the sphere is hidden behind the box. When I render, the entire background will be rendered, as will the sphere, and then the box on top of it. As a result, the time spent to render the entire sphere, as well as a part of the background, is wasted since it was unecessary. This happens regardless of whether or not double sided materials are used (although d.s. materials would additionally cause all occluded inside sides to be rendered as well), as well as whether raytracing of any kind is used...

I don't think I've seen anybody else before me complain about this, and I'm sure people know this doesn't happen with MAX/Maya, so I'm guessing it's a phenomenon I'm experiencing because of smth I have (not?) done...


11 November 2002, 08:06 PM
Can u post this scene and objects ?

11 November 2002, 08:20 PM
Originally posted by Jinxo

3) And to re-clarify, example : I have a box and a sphere. From the camera's POV, the sphere is hidden behind the box. When I render, the entire background will be rendered, as will the sphere, and then the box on top of it.

The ONLY time I've EVER seen that is if the other objects had any transparency set. IF you need them to be transparent and don't want that rendering in back, turn on trace transparency.

LW always renders non-transparent objects in a sphere from the camera out. The only time it will render something weird is when it first hits ONE polygon that is close to the camera and it extends back in to the scene past other objects.

11 November 2002, 08:50 PM
Ok. I think I'll go stick my head in the toilet...

My ignorance did get the better of me indeed. The transparancy raytracing seems to have done the trick in the current (fighter jet) scene. Good call, CG.p ! To think I'd avoided it in order to SAVE on render time (traditionally raytracing = baaaad)... :/

thnx guys


11 November 2002, 05:07 PM
Interesting topic, as I noticed this very same thing when I too had my first testrun with LW's renderer, and yeah it's annoying.

But I didn't really understand that fix CG.p wrote. Do you mean that I have to enable raytraced refractions? Or what?
Maybe it's just that I don't have LW on right now, so can't test it out.

Oh and I found a good example about this problem too, take a look at the scene "caller_id.lws" in the x:/LW/Scenes/Household folder. It renders the circuit board inside the machine before the plastic cover, looks funny :)

11 November 2002, 06:36 PM
Just checked this scene ...
Remove Transparency channel on "caller_body_top"(i don't know why this channel have map - the rander result is the same).

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