The material setup is a little more complicated than I would prefer, but this is as streamlined as I've been able to get it. Attached is an image of a summarized material setup. I use the Advanced Wood map in Explicit Map Channel mode, and control it with planar UVW maps. The idea, then is to get a darker material on the faces that are normal to the Z axis in UWV space. Here's how it works.
1. Create a wood material, and a second one with identical settings except for a darkened diffuse map.
2. Feed these materials into a Corona Layered Material, with the basic material in the Base and the darker one in Layer 1
3. Create a Corona Triplanar map for the Mask on Layer 1. It has to have the following settings:
a. X and Y colors are black, Z color is White
b. Blending set to 1
c. Mapping Space set to Reference Node
d. Scale set to 1
4. Create a Dummy helper. This will be used to control the orientation of the triplanar map.
5. Link the rotation of the Dummy to the rotation of the UVW map applied to objects in question.
6. Rotate the planar UVW map to the correct orientation, which should rotate the linked Dummy simultaneously.
This will put the dark faces in the right places, and give the correct blending from light to dark on angled or curved surfaces. It's a fair amount of work, and it requires a seperate Layered Material and Dummy object for every major grain direction in your model. I think that's still still less than UVW unwrapping, and saves the trouble of finding end grain bitmaps that match the rest of your wood. If anyone has ideas on how to streamline it, I would certainly appreciate them.
It's worth noting that this would be simpler if the Corona Triplanar map had a setting that made it respond to UVW mapping, but I understand why that's a counter-intuitive feature request.
