Last week I told you about how we were getting the terrain and objects to respond appropriately to direct light and shadows.  This week I will be showing you how the Phoenix Engine accounts for subtle indirect light, also called ambient light.  While standard shadowing is calculated by determining whether or not the sun can fire rays onto a texile, ambient lighting is determined by what percentage of the sky a texile has a direct line of sight to.  David designed his own calculation system to create the following ambient light map for the terrain:

Imagine the lighting outside on an overcast day.  There is no point source like the sun lighting the environment.  However, certain areas are light and others are darker.  As you can see above, all the peaks are white because they have access to the whole sky.  Areas in and around crevices are fairly dark.  Here is what the whole scene looks like when the terrain coloring textures, direct sunlight and ambient occlusion are all rendered together:

The result is that the terrain has a more plausible feel than before but there's still additional work to be done.   

For more Overgrowth develoment news, please check out the Wolfire Blog.