If you have multiple cameras you need to decide which one is the main camera for displaying results to the screen. The default is camera 0. However, if you add extra cameras they will also draw to the screen unless you use the set camera to image command (which may be what you need).
What's probably happening in your case is that you are doing something like the following:
set display mode desktop width(), desktop height(), 32
sync on : sync rate 60 : sync
autocam off
make camera 1
make object cube 1, 100
do
sync
loop
That just displays a green screen. The reason for that is that camera 0 is rendered first which will make the screen blue, but you don't see that because the system immediately renders camera 1 next and replaces the blue backdrop from camera 0 with the green backdrop from camera 1. The final colour drawn is what you see when the sync command has finished doing its work.
Here's another demo showing how to use the camera backdrop command (and a few other things
):
set display mode desktop width(), desktop height(), 32
sync on : sync rate 60 : sync
autocam off
make camera 1
set camera view 1, 0, 0, 200, 200
color backdrop 1, rgb(0, 64, 0) ` change the backdrop to dark green
make camera 2
set camera view 2, desktop width()-200, 0, desktop width(), 200
color backdrop 2, rgb(64,0, 0) ` change the backdrop to dark red
make camera 3
set camera view 3, 0, desktop height()-200, 200, desktop height()
make camera 4
set camera view 4, desktop width()-200, desktop height()-200, desktop width(), desktop height()
make object cube 1, 100
repeat
sync
until spacekey()
end
