Spinning Light Trick in Houdini ?

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Hi Everybody,

I'm looking for a way to reproduce the famous “spinning light trick” from Lightwave to Houdini, I don't know if mantra's motion blur is able to do it, so if anyone could point this out to me, it would be great .

Basically the spinning light trick consists to parent a light ( most of the time a spot) to a rotating null (frame 1 = 0°, frame 2 = 720 °, etc …) In that way if you turn on motion blur you'll get soft shadows, as the shadows are motion blurred The greater the distance is between the light and the null, softer will be the shadows .

I assume that Mantra's motion blur isn't working the same way than lightwave .

If anyone knows how to reproduce it ..


Thanks in advance !

Julien
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Oh yah - I remember reading about this somewhere. What was the purpose of the trick? I seem to recall it was a hack to accomplish something that the renderer couldn't do normally. If it's just moblurred shadows, you know that you can accomplish that with raytracing in mantra, right?

Cheers,

J.C.
John Coldrick
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Well, the purpose of this trick is to render blurred raytraced shadows (or shadow map one) very much faster than an area light for example . This illumination is also more diffuse as the light is moving .

I didn't know that you could render motion blurred RT shadows in Mantra, and I am knew to this renderer, so I assume that we can do spinning lights in Mantra, right ?

I was also wondering, maybe there is something to do with the Vex Builder shadows
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Oh right - now I remember - it was really an area light hack without all the cost. Gotcha.

The moblur thing wouldn't really be useful here, I think - a different issue.

Personally, I would just use area lights in Houdini(they're actually pseudo-area lights, but who's counting? ), but I can see how in certain circumstances performance might be a problem.

Sorry - haven't tried that(obviously ).

Post if you get it working and it seems all that much faster than area lights!

Cheers,

J.C.
John Coldrick
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I'll try to test it, but can you just explain how you get raytrayced motion blured shadows in Houdini ? After that I'll use the Lightwave technique for hacking the area lights


thanks John !
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It seems automatic to me - just throw down a v_rayshadow SHOP(VEX shadow shader), assign it to a light. If you have raytracing set on, it will blur.

Cheers,

J.C.
John Coldrick
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