Spot light PCF shadows
Out of all the different light sources we covered, adding shadow-casting support to spot lights is the easiest to accomplish. We will be using a technique based on the way projected textures are handled (covered in Chapter 1, Forward Lighting). This shadow-casting technique is called percentage-closer filtering (PCF).
The following screenshot features a side-by-side view of the same spot light with no shadows on the left-hand side and with shadows on the right-hand side:
One side benefit of shadows is that they help clarify the relative height between different scene elements. In the left image of the screenshot, it's hard to ...