Deeper can be very useful in creating more realistic billboards. One of the drawbacks of a regular billboard is that the light poorly interacts with it. When the lighting of a scene is computed, the pre-calculated shadow on the billboard isn’t. Adding a normal map to the billboard can improve the way the texture interacts with light, and self shadows are calculated using the actual lighting of the scene. We’ll see here how to quickly build a tree billboard that reacts to lighting.

To build the tree normal map, we use an actual 3D model made with Carrara’s Tree editor. The model is rendered with an isometric camera and just the ambient lighting to avoid any shadow in the texture map.
Note that in order to render the full geometry of the tree with the Normal Map renderer, the Full Detailed Mesh and the Show Leaves check boxes in the tree modeling window need to be checked. In order to render all the leaves, even the one oriented backward from the camera, the Flip Back Faces check box in the renderer parameters should also be checked.

Here are the 3 maps obtained.
dtut_treecolormap dtut_treenormalmap dtut_treeopacitymap

Color Map Opacity Map Normal Map

These 3 maps can now be used in a single shader for the billboard material. The shading tree is organized like that:
dtut_treeshadingtree

The billboard without or with the normal map look like these. The second one uses a normal map and shows some self-shadows.

tree1 tree2

Here’s a scene where the same billboard was repeated 10 times:
dtut_forestbig