Rhuarc :
Great work

How many FPS do you have , are they high ?
(it would be the case !)

Lot of people perhaps don't know, but texture projection
is heavy used in commercial games.
They are mainly used to project precalculated shadow , that's a lot more
fast then to project stencil shadows and you keep projection of shadow on ground and moving objects liek people , cars etc ....
And your projected shadow can be as complex as you want , the frame rate still
be the same (caus it's a bitmap not real polygon shadow)

For example you have a building and using stencil shadow to have shadow of building on floor and on moving people moving accross the shadow of it is really slow.

So what people do is use of lightmap for the building and a premade shadow bitmap, this way the projected shadow bitmap is projected on ground , objects and moving objects like cars,people etc ...
And without heavy cost on GPU like stencil shadows.

Another use can be shadow of tree leaves, but instead the more current use
is a decal that bend on polygons like in far cry palm trees.

(i hope Conitec will achieve the decal management one day, it's
very standard, old Unreal 2 engine already used that)

If you could you share your example ready to use , it would be cool