Double Illumination

[chadkruger]

Hi all,

Way back in my POV-Ray days, (Persistance of Vision Raytracer), I stumbled upon a very neat function.  It was called double_illuminate, which, essential made an object lit from both sides, even though light was only hitting it from one side.  I was able to create much more realistic effects on things like grass and leaves, because these objects in real life somewhat react to light this way.  My question is, does Terragen 2 support a similar function, or is there a way to create it?   This creates an especially more dramatic scene when things are backlit.  And if not, it is definately a feature I would like to request.

Thanks.

[old_blaggard]

You can use the "Transparency" effect in the default shader to achieve something like this.

[Tangled-Universe]

You can create a second sunlight opposite to your main sunlight with lower strength.

[PorcupineFloyd]

I believe that in case of leaves and small parts of vegetation this effect is called subsurface scattering. It would be hard to achieve such effect with simply making leaves transparent as they would in effect loss their solid form and look weird (transparent) and they should look rather like they are emitting the light or glowing.

[dandelO]

Translucency for leaves and grass works a treat in TG. Try levels beyond '1' if it's not enough.

[moodflow]

Subsurface scattering is the effect you are likely referring to, and its not yet implemented. 

Translucency in the default shader can be used to simulate this, for medium to distant shots.  For close up shots, it may or may not work as well. 

Additionally, using the luminosity function (also located in the default shader) can work well if set to subtle values, but will need to be based on "feel" and the local lighting.  So as the lighting is increased (ie. bright sunlight), you could use higher values, but as the light dims, sunset (or night), use low values, possibly even 0, else you'll notice the object emitting light and it will look like one of those glow toys.

I've used these two methods on a few scenes to substitute, and it works well "enough" until SSS is finally implemented.

[chadkruger]

Hmmm.  Still not sure if I'm describing it right.  I'm not talking about Global Illumination or ambient light, or something that is scattered into shadowed areas.  I use the leaves example because its one that is common and it is one of the only landscape uses for such a function.  If you look at a backlit tree in the real world, you can see the sun hitting the leaves even though the side that the light is hitting is facing away from you.  I'm guessing the guy who mentioned transparency has the right idea, just the wrong way to do it.  Just in the real world, the leaf isn't transparent, its just so thin, you can see the light through it, as well.  Just like if you hold up a sheet of paper to the sun and put your hand behind it, you'll see the shadow on the paper, even though both the light source and hand are hidden from your eye (the camera).  The paper is only lit from one side, but both sides are lit.  Apply this theory to a tree, and some leaves will be half lit, half shadowed, even though the light source is behind, the leaves will still be lit, etc.  The same would be true of grass.  I'm hoping Matt will read this, if he's the stickler for realism that I think he is.

Anyway, thanks for the suggestions, I'll keep trying a couple of things until I get it right, then.

[Hannes]

It has been already said. What you ask for is "translucency". It's in the dafault shader under the colour tab.
Here's an example with translucency set to 1.5 for the leaves:


Hope this helps

[chadkruger]

Oh, you better believe it helps.  Thanks!  Exactly what I was looking for.  I'm going to have fun with this.

[Matt]

As others have suggested, the "translucency" options in the Default Shader, Image Map Shader and Lambert Shader do exactly this "double illuminate" trick, but with even more options.