Using Gamemaker:Studio, I spent several hours this week working on my full screen shader affect for my latest game.  When I developed it, I had a problem with the way it displayed when I tested my game outside of windowed mode.  Once in full screen, the effect contained the entire screen , but shrunk in the corner with an overlay of the existing screen.  This definitely was not the desirable effect.

After reading up about drawing surfaces, I realized the problem was that my room has a smaller area (1280X704)  than the actual display dimensions (1600*900).  So the fix is to stretch the screen size to the display size.

Original Call –

if full_screen_effect draw_surface(application_surface,0,0);

Fixed Call-

if full_screen_effect draw_surface_stretched(application_surface,0,0,var_resolution_x,var_resolution_y);