Reactor wrote:
> stbenge <THI### [at] hotmailcom> wrote:
>> Or better yet, have a double_illuminate pigment block of its very own:
>>
>> object{
>>   leaf
>>   pigment{
>>    image_map{tga"leafy_image.tga"}
>>   }
>>   double_illuminate{
>>    image_map{tga"veiny_image.tga"}
>>   }
>> }
> 
> That is already possible using existing texture capability.  For "flat" shapes,
> using inside_texture will texture the "bottom."  double_illuminate changes the
> way the object responds to light_sources, and cannot directly be simulated via
> textures.

No, it's not the same at all. I've already considered this. 
inside_texture lets you specify the texture for the inside of an object, 
to be sure, but it does not simulate the *density* of its translucency.

Let's consider what happens when you have both an inside and outside 
texture with double_illuminate on a leaf object. When the light hits 
either side of the leaf, the diffuse will look exactly as it is 
intended, given the pigment/normal/finish you gave that side. This may 
be fine for many objects, but for a leaf, it is not very realistic.

By having a double_illuminate or translucency pigment block, you would 
be able to give the leaf a sort of "internal" density, without having to 
use media. In real life when light hits a leaf, the side receiving light 
directly will *reflect* the light back to the viewer. The veins in the 
leaf will often look lighter in color than the rest of the leaf. The 
other side, however, will look pretty much opposite to that, since the 
veins are thicker than the rest of the leaf. The veins will appear dark. 
You can simulate this, as you said, using inside_texture, but what 
happens when you want to light the leaf from the other side? The effect 
will break, and the result will not at all look realistic. The only 
solution here (as POV is now) is to make the leaf thick and give it 
scattering and absorbing media. This, as we all know by now, is very 
slow to render! There is also a problem with the leaf appearing 
transparent, and to remedy this problem very high media settings would 
be required.

A fast-rendering solution to this would be to have a double_illuminate 
or translucency pigment block, probably one for each texture and 
inside_texture. Simply giving the leaf inside and outside textures will 
not work as intended. Most programs have a translucency material layer, 
and I think POV-Ray will have to have one of its own to match the 
rendering capabilities of other programs.

Sam

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