Shadows, Part II

Happy new years and hope everyone had a good holiday.

I have been working on the shadows on and off during the last couple of days and there is now a huge improvement over the existing shadowing system.

-------- WARNING: somewhat technical stuff below -------

In my previous post, I demonstrated the difficulty in picking an appropriate shadow map size to fit the scene. A small shadow map gives nicer shadows but the shadow is only visible in a limited distance. A large shadow map covers the entire scene but the shadows are super low quality.

Fortunately, the solution is rather simple (in theory). Rather than using only one shadow map, why not use multiple shadow maps of increasing sizes instead? Always select the smallest shadow map if possible for the best shadow quality. The largest shadow map covers the entire view frustum, and thus guaranteeing every object will be shadowed. This technique is known as Cascaded Shadow Maps for those that want to do a little more googling themselves. 

And here it is, with debugging helpers enabled:

The 4 pictures at bottom left are the 4 different shadow maps used to shadow the scene.

The scene is tinted with colors to indicator which shadow map is selected for the shadow calculation. Red - smallest map, green - 2nd smallest and so on.

Here it is in action: 

All 3 pictures are taken with the same shadow setting. Compared to the single shadow map system, this new system allows for high quality shadows when viewed close up, while also shadows distant objects as well.

Getting this new shadowing system to work is extremely important, because it allows for more open areas and environments rather than just small rooms and corridors (to hide the fact that shadows had a limited range).

For example, a "forest":

When zoomed out: