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Can't add black to material using lerp. Ends up transparent. What's the alternative?

Trying to add a shadow to my masked out moon using the same mask but with an offset. Instead of creating a shadow it makes it half transparent. Now I have floating bananas.

I don't get it, the lerp node asks for an alpha. I just want it to use the alpha to blend, I don't want it to ask for a second opinion from the texture sample.

Any solution?

Changing the shadow colour from black to red yields this result:

Resolved, fixed working moon.

Product Version: UE 4.11
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asked May 15 '16 at 11:38 AM in Rendering

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Grant Margison
86 7 14 21

avatar image tbone240195 May 15 '16 at 11:55 AM

Can we see your material?

avatar image Grant Margison May 15 '16 at 12:11 PM

Ignore the yellow, the sun's not a problem.

avatar image tbone240195 May 15 '16 at 12:13 PM

If I look closely your moon has the sun color, and the moon color looks to be used as opacity.

avatar image Grant Margison May 15 '16 at 12:36 PM

The moon is slightly off coloured from the sun, indeed. I just don't think linear Interpolate recognises black as a valid colour to add. Does it?

avatar image tbone240195 May 15 '16 at 12:42 PM

It does, but I don't see where your nodes go to. Also what is the material? opaque? It looks like it's masked or so.

avatar image Grant Margison May 15 '16 at 12:54 PM

It's opaque. It's a standard sky sphere with the exception of the nodes in the screenshots. The material was an unlit material, meaning only an emissive node. I thought to myself, black doesn't emit, maybe that's the problem, so I changed to default lit and there's literally no difference in blending. It's got to be something to do with the lerp's, if I change the colour from black to bright red, it works. Problem is, I don't want a bright red shadow lol.

avatar image tbone240195 May 15 '16 at 01:06 PM

Can you show where everything is plugged in? It's hard to debug without seeing the complete picture

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1 answer: sort voted first

Hope all goes well man, good luck!

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answered May 15 '16 at 02:53 PM

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tbone240195
46 3 3 7

avatar image Grant Margison May 16 '16 at 04:46 PM

Linear Interpolation doesn't add black colour from B to A based on alpha, it removes colour from A based on alpha. I was removing colour from the moon only and as a result it looked transparent where the shadow was. I needed to remove colour from the stars as well but not the clouds.

It is a pain in the ass, there's no denying that, I wish I could just say add black to A based on alpha but no. There must be another way.

I any case, sorting the layering out so I was using lerp to remove colour from the moon and stars yielded success. Working with sphere masks for the moon is a nightmare but I ended up getting these results http://imgur.com/a/3j5gI

It's ok, well no It's pretty bad to be honest, it's so bland it doesn't fit with the world, lacking texture.

I think I'm going to try a static mesh instead, offset far away from a centre pivot and just rotate that when I'm rotating the moonlight. Not sure how to go about the Earth shadows on it yet.

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