Use the WASD keys to move the player around and your mouse to aim and shoot.
The BFG9000! Oh, yes. The big, uh, freakin' gun from the classic Doom games is a pretty misunderstood and complex weapon.
It has a unique mechanic which not many people seem to understand.
This visualiser should help you with understanding the mechanics behind the BFG9000 to optimise your demon kill count.
Don't mind me, just upping my demon kill count.
Whenever a BFG ball is shot by the player, its vector is stored.
Once the BFG ball hits a wall or object and detonates, 40 invisible tracers are shot from the player's origin in a cone-shaped area of around 45 degrees.
The direction of these tracers are based on the vector that was stored earlier on.
This means the tracers aren't affected by the player's current direction.
You could even emit these tracers by facing your back to your enemies, as long as the BFG projectile vector corresponds with the direction your enemies are in.
BFG9000's original source code can be found here.