2. If I do c_fuchsia on the draw_clear_alpha, the screen does turn that colour.
Are you 100% sure you draw to the surface when doing this? It sounds like the symptom of not surface_set_target-ing it first (clearing the entire screen instead of the surface). And not surface_set_target-ing it would also explain why nothing is drawn to it.
I think I've spotted the issue - when you set the drawing target to a surface, 0,0 is the top left corner of the surface. However, you don't always draw the surface at the 0,0 room coordinate, so drawing sprites at x,y will displace them with whatever the view top-left corner currently is. Draw the shadow sprites at x-cx, y-cy instead and it should work. (It probably worked when you did it in a separate room since you didn't move the view away from the top-left corner)
You're a genius! It worked! Thanks so much, such a simple thing gave me such a headache. Lol
