BOB UPDATE is now used as the standard technique in the vast majority of AMOS arcade games.
If you need to restore the re-drawing system to its default status, BOB UPDATE ON sets the situation back to normal. One word of warning though, if you are already swapping the screens manually with SCREEN SWAP, use BOB UPDATE carefully, because it will switch between the logical and physical screens immediately after your Bobs have been updated. The simplest remedy for any problems this may cause is to use BOB CLEAR and BOB DRAW instead. These are explained later.
SPRITE UPDATE
instruction: move all Sprites at once
Sprite Update
Sprite Update Off
Sprite Update On
You may want to remind yourself of this family of commands, which are explained in Chapter 7.1. They parallel the BOB UPDATE commands, and are used in the same way.
You are recommended to add a WAIT VBL instruction after each SPRITE UPDATE, to make sure that Sprite movements are perfectly synchronised with the existing screen display.
UPDATE
instruction: move all objects at once
Update
Update Off
Update On
The UPDATE commands are a combination of the BOB UPDATE and SPRITE UPDATE families, and they are used to re-draw all objects on the screen in a single operation. UPDATE OFF turns off the automatic re-drawing system, so that any Bob or Sprite commands will appear to be completely ignored. In actual fact, they are still going on invisibly, in the background.
UPDATE displays any objects which have moved since the last update. You are recommended to add a WAIT VBL instruction to ensure a smooth effect.
UPDATE ON returns the updating system back to the original automatic setting.