			READ-ME



	"Real Time Graphics for the Atari ST".

There are a few small differences between the files listed in the book
and the files on the disc, primarily to improve their compatability 
with version 1 of the Devpac assembler. These are described below.



THE FILES IN THE BOOK

The files in the book were written and assembled using Hisoft's Devpac
assembler version 2. The assembled programs can be run from within the
assembler and are terminated by a key press using

	clr.w	-(sp)	BDOS call p_term_o
	trap	#1	

so that control returned to the assembler.

The programs in the book use this method.


THE FILES ON THE DISC

With version 1 of the assembler it is necessary to assemble programs to
disc. The program is then run in the usual way by double clicking on
the icon. Since many of the later programs use screen buffering, where 2
screens are alternated to avoid flicker together special colours,
it is necessary to reset the screen and return to the desktop on 
exiting a program. The programs on the disc use the following routine 
to do all of these in succession 

* make just one screen
	move.w	#-1,-(sp)	
	move.l	screen2,-(sp)	screen 2 is physical
	move.l	screen2,-(sp)	and logical screen
	move.w	#5,-(sp)	XBIOS call
	trap	#14		setscreen
	add.l	#12,sp		tidy stack
* reset the colours
	pea	std_pal
	move.w	#6,-(sp)
	trap	#14
	add.w	#6,sp
* return to desktop
	move.w	#$4c,-(sp)	BDOS call p_term
	trap	#1	

Programs on the disc work OK with either version 1 or version 2 of 
the assembler.
  

