Fade in/out object or material alpha

Support Materials and Textures
#1

Hi Blenderheads,
Trying to achieve a particular fade in/out effect, but I’m not sure it’s possible without compositing.

Simply, I want to fade in/out objects in Blender. But, I don’t want the glass type effect where you can see parts of the object through itself. This image shows what I mean:

man_transparency
man_transparency1737×744 283 KB

I thought this was probably impossible without compositing, but playing Warcraft last night I realised Blizzard has found a way of doing this in game:

wow_transparency
wow_transparency2636×489 120 KB

It may be this is some gaming wizardly and not possible in Blender. But I’m hoping someone has a solution. I’m really trying to avoid compositing, as I have dozens of objects that all overlap each other, which would be a nightmare to composite.

-Jamie.

#2

You can try backface culling on the material so the inner faces won’t be visible.

#3

Backface culling only works when the faces are actually facing away (ie. the normals). So the eyes are INTERNAL faces, but technically not BACKFACING.

The top image actually has backface culling turned on.

1 Like
#4

Okay, made some significant progress.

Changing the BlendMode from AlphaHashed to AlphaBlend brings up this previously hidden option “show backface”. And checking that completely fixes the issue…in Eevee.

The problem is…I’m using Cycles. And unfortunately I HAVE to use Cycles for the realism.

Anyone know where this same option is in Cycles?

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image1990×643 265 KB

#5

Cycles doesn’t work the same as Eevee, not in the slightest, not when it comes to something like this.

If you change the transparency BSDF to a refraction BSDF (at IOR 1.0 for no refraction), then you could give the objects a mix with 1.0 transparency for transmission rays from a light paths node. But that’s assuming you don’t have any other refractors in the scene.

image
image3753×2160 987 KB

Split screen demo, occluding on the left, not on the right.

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#6

Holy cr*p, dude! I think that might have actually worked.

I played around with your setup a bit and I think I’ve found something that works. Must confess, not 100% sure what’s going on mathmatically, but I’ll take ‘working’ right now as a win.

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image1584×789 196 KB

Just as a heads up to anyone in the future, cranking your mix shader up to 1 still leaves you with a slight shadowed effect on the object:

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image1783×898 256 KB

But adding another transparency shader at the end gets rid of it. And you can hook up a ‘value’ node to control both mix shaders at the same time, making animation easier.

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image1631×868 228 KB

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#7

It shoots rays from the camera. These are camera rays until they hit something, and unfortunately, transparent doesn’t count, doesn’t change them into anything. (Why do we have transparency bounces then? Beats me.) When they hit a refraction BSDF, they continue on as transmission rays. So when they hit your front faces, the camera rays turn into transmission rays. They continue on, hitting a backface, then maybe another frontface and another backface-- but since these are transmission rays, the material gets evaluated as fully transparent, so it doesn’t do anything at all to the ray, no coloring, no bouncing/refracting of it, and the ray continues on its merry way until it hits something “real”.

2 Likes
#8

Great explanation - I understand that now.

That’s basically what I’ve been trying to do this whole time, but I had no idea transparency rays didn’t count and was just assuming the feature wasn’t available. Very clever ‘cheat’ to convert transparency to transmission :wink: