When you close this door, the room lights up. The door itself is the light source. It's a simple effect, but a lot of shading could be involved for it to look high quality. Check the "References - FAQ" section for details on the technicalities of lighting effects.
Create two rooms and a door joining them. Tag the door sector
[0,20]. The two rooms are to be lit up, and the door itself acts as the light source. Placing columns allows for nicer looking shading effects. Behind every column should be a 'shadow' sector which will stay dark when the room lights up. Since this is only a demonstration, I'm keeping things simple.
Texture your rooms and door frame. Shade the rooms as dark as they will be when there is no light source. Temporarily lower the ceiling so you can texture the door with lights, and tag both of its walls
[1,0]. Giving a wall a Hi-Tag of 1 excludes that wall from shading effects (forcing its shade to remain constant). Now you can raise the door's ceiling back up again (the door must be initially open).
Place the following sprites in the door sector:
S[Channel,9], M[StopSound,StartSound] (
S[Delay,10]). Place an
S[Channel,9] in all of the sectors which will be brightened when the door closes. Set the shade of each
S[Channel,9] to how bright that respective sector will be when the door is closed.
Now you can fine-tune and test the effect in the game.