Light doesn't shine through alpha-map

…and back again

i’ve been working on a water simulation lately.

In the background I added some mint leaves. pretty simple: A planeAA on which I mapped the mint texture. So I used an alpha-map to cut out the shape.

My problem: the light isn’t shining through the leaves. The shadow looks kinda weird.
.blend file
Any help?

there is a wiki on this

but i think you need raytrace and spot light for this effect to work

happy 2.5

I probably found the page you talked about.
So i give a try on this

I believe it’s from the AO, not from the lamps. I’m afraid you need to exclude them from the AO. But since you want them to cast rayshadows, you can’t simply turn off Traceable.

Btw, in the materials of the leaves, just set the Alpha to Ztransparancy and the Specular slider to zero.

I’m with Sago – it’s the AO. You could use Approximate AO instead of Raytraced, and you can uncheck the “Cast Approximate” box. But then you may not get the shading you need. If the shadows are soft enough, you could uncheck “traceable” and disable all shadows for your leaves, then build a mesh just underneath your leaves that roughly follows the alpha contours. Then give it a new material and set its shadow to “cast only” and make sure traceable is enabled.

OR… you can tweak your existing mesh so it is nearly the size/shape of the leaf and put the material on that instead. Then you’d only need one mesh.

IMO, Alpha channels are still a bit of a pain in Blender, and whenever you can use a mesh instead, you should. Your rendering options are increased many times.

I took a tutorial for almost this exact thing at BlenderCookie ( and in it I made a leaf that the shadows worked perfectly fine on. I cant remember exactly how, unfortunately, I need to go back and brush up on it. But if you want the blend file for the tree I made, I would be more than happy to send it your way as well.

exactly! it was because of the AO. I didn’t find a solution for myself yet. for now I just faked AO with some other lamps. when I have time I will try benu’s way.

anyways, thanks a lot!!

@Aericks: that would be really nice! If you want you will find my e-mail in my profile. thanks! (or just post it…)

Well, we all know how this would work “in the real world,” but this isn’t “the real world.” It’s computer graphics.

Therefore, we can illuminate the tabletop evenly with a light that is a “layer light,” so it does not “see” the leaves. We can illuminate the leaves with another “layer light” that sees only the leaves, and we can extract the shadow component from that light and (with an appropriate nodes “noodle”) use that to attenuate the first light in the appropriate areas.

Oh, call it “cheating a shot” if you want to… but tricks like these can make a huge difference in rendering times, and they probably altogether avoid the more-expensive calculations. (For that matter, you can render the leaves completely separately, then composite them into the final image along with the shadows, etc, thereby giving yourself complete control over the color-balance of the entire completed image. At all times you only need to recalculate those portions of the image that actually need your attention; almost never must you re-render the entire shot.

Rather than attempting to get one setup that perfectly dealt with the leaves and the ice and the fruit and the table (a very difficult challenge, given the dramatically different surface characteristics of each of these), I would render each one of these things separately, into MultiLayer files, then mix them down into the final image. Ought to be the work of an afternoon.