flashing

How can I flash the screen to indicate gun fire?

I think this simple approach may be what your after.

CameraClsColor nameofcamera, 255, 255, 255
or even ClsColor And have them in place where you'd like the change to take place. And reset the colors back to black or what have you once finished checking for firing.

Hope it helps

Create a sprite, position it so that it takes up the current viewport, and use entity order to make sure it is drawn last over everything else. Use additive blend mode and when you want it to flash change the color of the sprite to white/yellow etc and change it back to black when the gun is not firing, or between flashes.