I find it all a bit confusing myself but I got it working using "Paste Image" in the end:
function setup_fullscreen_effect(effect$, camera, image, effectnum, fov)
`create the camera
make camera camera
set camera range camera,10,1000000
set camera fov camera,fov
load camera effect effect$, camera, 0
set camera effect camera, effectnum, image
endfunction
function update_fullscreen_effect(camera, image)
position camera camera, camera position x(0),camera position y(0),camera position z(0)
rotate camera camera, camera angle x(0),camera angle y(0),camera angle z(0)
REM call just before "sync"
`render the original screen and copy to image
sync camera 1
`render the final screen image
sync mask camera `render camera 0 only
`paste to screen
paste image image, 0,0
endfunction
Example code:
`before the loop
setup_fullscreen_effect("FX/Bloom.fx", 1, 2, 1, 70)
`during the loop
update_fullscreen_effect(1, 2)
