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VRay and shadows
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VRay and shadows // Archive: Tech Forum
Post by Emmanuel // Apr 25, 2006, 11:47pm
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Emmanuel
Total Posts: 439
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When adding plants in an indoors rendering, we often use a transparency map and a texture of a plant, like in the rendering below (lightworks rendering).
With Lightworks or Virtualight, the shadow casted by the alpha map is always sharp, even is we set a low sharpness in the option panel.
When all of the other shadows in the picture are soft, this is unatural.
How does V-Ray manage the transparency map shadows ? |
Post by parva // Apr 26, 2006, 12:35am
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parva
Total Posts: 822
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With Lightworks or Virtualight, the shadow casted by the alpha map is always sharp, even is we set a low sharpness in the option panel.?
Lightworks area light can only cast soft shadows. Other shadows are "hard" raytraced shadows or you use mapped shadows where you can set the map size and blurring of the map (that I guess is the reason why your sharpness settings have no effect - maybe used raytrace shadows instead of mapped ones?).
How does V-Ray manage the transparency map shadows ?
Vray is a raytracer.
You can enable/disable soft shadows for nearly every light and vray use a sampling algorithm to smooth the shadows in distance/size you have set.
HTH |
Post by TomG // Apr 26, 2006, 1:53am
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TomG
Total Posts: 3397
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You can't use Shadow Maps with transparency shadows. Enabling transparent shadows makes the light into a Raytrace light as that is the only way to calculate the shadows, and so any settings for Shadow Maps such as Low Sharpness will have no effect - they are overriden by the transparent shadows setting forcing it into being a raytrace light.
Area Lights give soft shadows under Lightworks as they are actually an array of light sources. You can create your own array of light sources too if you like. This will generate soft shadows from the overlapping shadows of the lights. You can use an IBL scaled down very small too for another way of getting an array of light sources. Render time goes up of course.
There is also the "spinning light with motion blur" approach, which renders and combines multiple versions of the same frame into one frame.
V-Ray is a different thing altogether and does not use shadow maps at all. All of its effects are done in raytracing, so it is possible to use soft shadows with transparency maps, as the soft shadows are not done via mapped shadows.
HTH!
Tom |
Post by daybe // Apr 26, 2006, 2:22am
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daybe
Total Posts: 562
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Hey Tom I had never thought of that before thanks for the tip.
There is also the "spinning light with motion blur" approach, which renders and combines multiple versions of the same frame into one frame.
Cheers |
Post by TomG // Apr 26, 2006, 2:29am
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TomG
Total Posts: 3397
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Most welcome! Just to elaborate, this is a local light which spins around an axis that is away from its own center (so it revolves like a planet around a sun, not revolves like the planet spinning on its own axis).
Often you would use two local lights (omni lights), slightly apart from each other, and they'd rotate about the point in the middle.
This is the same idea as an array of lights of course, just the array is spread out in "time" rather than spread out in "space" :)
HTH!
Tom
PS - some more about shadows. Shadow Mapped shadows are equally soft and equally blurry, right at the base of a shadow casting object, and far away. However, the raytrace approach with an array of lights (be it an area light, small IBL, array you build yourself, or spinning lights) will create a realistic effect, where shadows are sharp when close to the shadow casting object, and get softer the further away they fall from the casting object.
V-Ray's Soft Shadows option does this realistic increase in blurring with distance too.
This makes the raytraced approaches take longer to render, but does make them more effective, accurate and realistic.
HTH!
Tom |
Post by Loadus // Apr 26, 2006, 7:32am
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Loadus
Total Posts: 44
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There is also the "spinning light with motion blur" approach...
Weeeeee. Cheers, T! That's a sweet trick. I've always tinkered with light arrays, but blending them like that never occured to me. |
Post by noko // Apr 26, 2006, 11:23am
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noko
Total Posts: 684
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Cool! I like the spinning light idea with motion blur must try :). |
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