"Isn't there a way to simply use the distance from the light to the shadow quad to set the opaqueness of the shadow quad, using the same tone for all 4 vertices of the quad?"
I'm not sure what exactly you're talking about and right now I am starving and can't think. But I did update the system quite a while ago to clip the polygons that fall in the shadow volume so the size of the tris that the shadow falls on should not affect its appearance any more. And the falloff... That's caluclated per vertex. And the shadows are not projected onto quads, they are projected onto arbitrary shapes that look like a quad from the view of the light source, but in actuality, are often no such thing.
I'm not sure what exactly you're talking about and right now I am starving and can't think. But I did update the system quite a while ago to clip the polygons that fall in the shadow volume so the size of the tris that the shadow falls on should not affect its appearance any more. And the falloff... That's caluclated per vertex. And the shadows are not projected onto quads, they are projected onto arbitrary shapes that look like a quad from the view of the light source, but in actuality, are often no such thing.