This is the command that swaps over the physical and logical screens, so that the displays are instantly switched between the two of. them. If the DOUBLE BUFFER command has been engaged, this process is automatic.
LOGBASE
function: return the address of logical screen bit-plane
address=Logbase(plane)
The LOGBASE function allows expert programmers to access the Amiga's screen memory directly. The current screen is made up of six possible bit-planes, and after LOGBASE has been called, the address of the required plane is returned, or zero is given if it does not exist.
PHYBASE
function: return the address of the current screen
address=Phybase(plane)
PHYBASE returns the address in memory of the specified bit-plane number for the current screen. If this plane does not exist, a value of zero is given. For example:
X> Loke Phybase(0),0 : Rem Poke a thin line directly onto screen
PHYSIC
function: return identification number for physical screen
number=Physic
number=Physic(screen number)
The PHYSIC function returns an identification number for the current physical screen. This number allows you to access the physical image being displayed by the automatic DOUBLE BUFFER system, and the result of this function can be substituted for the screen number in ZOOM, APPEAR and SCREEN COPY commands. The PHYSIC identification number of the current screen will be returned, unless an optional screen number is specified.
LOGIC
function: return identification number for logical screen
number=Logic
number=Logic(screen number)
Use the LOGIC function to get an identification number for the current logical screen, or use an optional screen number to specify a particular logical screen. The identification number that is returned can now be used with the ZOOM, APPEAR and SCREEN COPY commands, to change images off screen, without affecting the current display.
Screen synchronisation
It has already been explained that the image on your screen is updated fifty times every second.
A single update consists of an image drawn by an electron beam scanning across every line of
the screen until it reaches the bottom right-hand corner, at which point the beam switches off