Lighting #2 Occlusion Shadows
In 3D digital rendering, a useful render technique is called A.O. rendering, where A.O. stands for Ambient Occlusion. They look generally very white, but the shadows can be very deep.
For example, an example from unity doc, https://docs.unity3d.com/Packagesfirstname.lastname@example.org/manual/Ambient-Occlusion.html
Another example from https://vr.arvilab.com/blog/ambient-occlusion
The principle for A.O. rendering is that we assume lights comes from everywhere with equal illumination. Only the places where light can't get in are shown in very dark shadows.
The principle for the A.O. shadow is that, when surfaces are getting closer to each other, they produce a shadow. The more distant they are, the softer the shadows are. Otherwise, the shadows can be as dark as black.
But, notice that these shadows are not created by casting lights so they are not projections; they are there because the light getting in are attenuating.
Again, let's take the indoor scene and the character in the previous note as examples.
Example 1 Indoor Scene
Notice how the shadows are getting deep in the areas where light can't get in.
By multiplying the A.O. shadows with the grayscale surface orientation we had in the previous shading step, a more realistic render of the indoor could be achieved.
[ Before Applying A.O.]
[ After Applying A.O.]
Notice how soft shadows are placed in this scene.