Variations of outline, overlay, glow and see-through or X-ray vision effects are quite common in 3D games today. Highlight Plus is an asset for the Unity platform that provides an all-in-one approach for these effects.
The See-Through or X-ray vision effect, makes hidden stuff or enemies partial or fully visible through opaque geometry like walls. Usually, this is implemented as a shader trick in which a simple “ZTest Greater” can be used to render the occluded object.
Highlight Plus allows you to combine one or more effects of this category by just adding the “Highlight Effect” script to any number of gameobjects (or hierarchy of objects by placing it on a root gameobject).
However, in Highlight Plus we went a bit further and implemented what we call “Ordered See-Through”. This technique keeps objects relative depth even when occluded producing a valid effect when two or more hidden objects overlap behind an opaque wall for example.
In the clip above the cylinder moves from behind the sphere to the middle position between the sphere and the checkers wall. Notice that at all times, both sphere and cylinder objects are behind the wall. Using the classic ZTest approach will make the cylinder render on top of everything else which would be wrong in this case when the sphere is between it and the wall.