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Translucent Shadows with Directional Light

I am having some trouble with a translucent shadow test and I hoped someone here might be able to help me. I have managed to make something similar to the stained window described here. I managed to make it work well enough with a spot light (though it is a bit resource intensive to build the lights).

So I thought I would try it out with a directional light. Using the standard settings for a directional light however, resulted in a pretty blurry image.

Directional Light with standard Source Angle

The article I linked earlier does warn us about the light source angle of the light. Thinking this was the issue, I changed it to 0, but it doesn't seen to have had much effect.

Directional Light with Source Angle set to 0

Neither does the issue seem to be the lightmap resolution. The plane on which the light is being projected in those images had its lightmap resolution overridden to 1K. Still, I tried doubling it and this is what I got:

Light Map resolution of 2048x2048

Which seems pretty much the same to me. Am I missing something about how the translucent shadows are supposed to work? My glass window was made using a simple plane with a two-sided, unlit modulating material. It just connects a texture to the emissive input, multiplied by an "intensity" number, to make the projection more clear.

By the way, I tried rebuilding the lights with a source angle of 5 to see if it would make the image significantly more blurry. The result was not much different either:

Directional Light with Source Angle set to 0

The result is slightly more blurry, so it is not like the angle is not having an effect.

Thank you for reading this question through!

Product Version: UE 4.22
standard-sun.png (706.3 kB)
0ss-sun.png (584.1 kB)
2kplane.png (603.4 kB)
5ss-sun.png (557.2 kB)
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asked May 06 '19 at 03:33 PM in Rendering

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avatar image Alex_AB May 06 '19 at 04:54 PM

By the way, here is an screencap of a spot light with the same stained glass window. This is more or less what I expected with the directional light experiment.

Translucent Shadows with a spotlight

spotlight.png (788.5 kB)
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