Hello,
After getting seasons working properly in the Cubecity prototype, I've now managed to implement what I've learnt there into Atmocity and fully implemented a year cycle.
Grass is now mapped via the alpha channel on building footprint textures. The grass area has a black and white area with baked lighting on top of which a grass texture is then added. This allows me to easily set the color of the grass according to what season we're in.
Trees work in a similar fashion, except I divide the tree texture into several distinct channels. The red channel is used for the tree shades. The green channel marks what areas are constant, ie the stem of the tree or if it's a pine tree then the entire tree. The alpha channel is used for cutout. A gradient is then used and sent to the shader to determine the color of the leaves and the alpha whether the leaves are on or off as the year progresses. When the alpha drops, trees shed their leaves, as in winter.
