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Asm Utility Speeds Screen Blanking

By Dave Kelly, Engineer, General Dynamics, MacTutor Editorial Board

For those that remember Professor Mac's Screen Pokes presented in the April 1985 issue of MacTutor, we discussed the Macintosh screen and how to poke the screen to all blank. The method presented there was very slow. Until such time as someone comes out with a MS BASIC compiler most routines will be slow. MacTutor now has a call out to anyone that has a complier for MS BASIC to step forward and become famous. Please contact us if you have any information to give us about compiled BASIC.

This month we will provide the alternative screen poke method using a library written in 68000 code. These routines were designed to work with the 512K or 128K versions of the Macintosh, however, the code may be modified to be used with other memory sizes.

If you are unfamiliar with BASIC libraries then we recommend that you refer to the BASIC School article in the November 1985 MacTutor on Building a Machine Language Library routine. (Back issues are available). The listings that follow are assembled in the same manner as discussed in that column.

There are three code routines that you need to be concerned with. The LIBinit.asm (Listing 1) routine may be found on page 44 of the Nov. 85 MacTutor. The second routine stores $FFFFFFFF in all screen locations, thus blacking out the entire screen. The third routine inverts all of the screen locations. We thank Serge Rostan of Pontoise, France for contributing the main code for the invert routine.[If you have some good ideas on Basic, please write Dave care of MacTutor and see them in print. -Ed]

The BlankScreen routine (Listing 2) is accessed by the statement: CALL BlankScreen (memory%) where memory% is the memory of your particular system (i. e. use memory%=512 or memory%=128). This routine works fine for 512K or 128K Macs, but you will have to change the equates for Screen512 and/or Screen128 (see listing 2) in order to accomodate other memory sizes. The equates 'GetNextLibArg', 'IntegerArg' and 'BasicError' are BASIC routines defined in BMLL (Microsoft's Building Machine Language Libraries) which library routines may call. The BlankScreen routine reads the memory% parameter and determines the screen location. Then each location is loaded with $FFFFFFFF and the screen is blank. The routine then returns back to the calling program.

The InvertScreen routine (Listing 3) works much the same as the BlankScreen routine. You may call the routine with the statement: CALL InvertScreen (memory%). The passed integer variable memory% is the same as in the BlankScreen routine. The only difference in this routine is that each memory location is exclusive-ored with the value $FFFFFFFF.

Listing 4 and 5 are the Linker and Resource complier files needed by the MDS system to create the library resource file. See Nov 1985 MacTutor for details on how to us these files.

The Screen Demo program in listing 6 demonstrates the use of the BlankScreen and InvertScreen routines. It is advisable but not mandatory that you hide the cursor using HIDECURSOR before blanking or inverting the screen. The cursor may be turned on again with the SHOWCURSOR statement. If the cursor is not disabled then the 16 X 16 cursor location will not be blanked or inverted properly. These libraries may be used to create special effects in your program such as flashing the screen.

Expanding BASIC using library routines greatly improves the capabilities of your programs. If you have a favorite library routine, please send it to us. We would like to share more libraries with other useful purposes.

LISTING 1
;LIBinit routine (See MacTutor Nov. 1985 pg. 44 for comments)
;save as LIBinit.asm

LIBVER_Result  EQU 6
LIBinit:
 CLR.W  LIBVER_Result(a0)
LIBinitExit:
 MOVEQ  #0,d0
 RTS


LISTING 2
; BASIC BlankScreen Library Source Code
; By Dave Kelly
; MacTutor 1985

;Synopsis:
;CALL BlankScreen (memory%)
;Output:

GetNextLibArg  EQU $2A
IntegerArgEQU  $32
BasicErrorEQU  $42
Screen512 EQU  ((512-128)*1024)+108288
Screen128 EQU  108288

 
 JSR  GetNextLibArg(a5) ;Get the next argument
 JSR  IntegerArg(a5) ;[d3:w] = integer error if arg
 ;can't be forced into an 
 ;integer.
 CMP.W  #128,d3
 BEQ  Do128 ;branch if 128K memory
 CMP.W  #512,d3
 BEQ  Do512 ;branch if 512K memory
Device_Unavailable:
 MOVEQ  #68,d2   ;Device Unavailable error
 JSR  BasicError(a5)
Do512:
 LEA  Screen512,A0
 BRA  Blank
Do128:
 LEA  Screen128,A0
Blank:
 MOVE.W #5472-1,d1 ;setup high screen address
 MOVE.L #$FFFFFFFF,d0;move to d0
Loop:
 MOVE.L d0,(A0)+ ;set screen address to d0
 DBRA d1,Loop
 RTS
GetIntegerVar:
 JSR  GetNextLibArg(a5) ;Get the next argument
 JSR  IntegerArg(a5) ;[d3:w] = integer error if arg
 ;can't be forced into an 
 ;integer
 RTS    
LISTING 3
; BASIC InvertScreen Library Source Code
; By Dave Kelly
; MacTutor 1985
;save InvertScreen.asm

;Synopsis:
;CALL InvertScreen ( memory%)
;Output:

GetNextLibArg  EQU $2A
IntegerArgEQU  $32
BasicErrorEQU  $42
Screen512 EQU  ((512-128)*1024)+108288
Screen128 EQU  108288

 
 BSR  GetIntegerVar;integer arg in [d3:w]
 CMP.W  #128,d3
 BEQ  Do128 ;branch if 128K memory
 CMP.W  #512,d3
 BEQ  Do512 ;branch if 512K memory
Device_Unavailable:
 MOVEQ  #68,d2   ;Device Unavailable error
 JSR  BasicError(a5)
Do512:
 LEA  Screen512,A0
 BRA  Invert
Do128:
 LEA  Screen128,A0
Invert:
 MOVE.W #5472-1,D1
 MOVE.L #$FFFFFFFF,D0
Loop:
 EOR.L  D0,(A0)+
 DBRA D1,Loop
 RTS
GetIntegerVar:
 JSR  GetNextLibArg(a5) ;Get the next argument
 JSR  IntegerArg(a5) ;[d3:w] = integer (error if arg
 ;can't be forced into an 
 ;integer
 RTS    
LISTING 4
;Screen Library Link
;MacTutor 1986

/OUTPUT ScreenLib
LIBinit.Rel
<
InvertScreen.Rel
<
BlankScreen.Rel
$

LISTING 5
ScreenLib.Rsrc
BLIB
TYPE CODE = GNRL
LIBinit,1
.R
ScreenLib CODE 1

TYPE CODE = GNRL
InvertScreen,2
.R
ScreenLib CODE 2

TYPE CODE = GNRL
BlankScreen,3
.R
ScreenLib CODE 3
LISTING 6
'Screen Demo
'By Dave Kelly
'©MacTutor 1986

LIBRARY "Screen Demo"
mem%=128:IF FRE(0)>75000! THEN mem%=512
GOSUB Setmenubar
MENU ON
ON MENU GOSUB menucheck
loop: GOTO loop
menucheck:
    menunumber=MENU(0):IF menunumber<>6 THEN RETURN
    menuitem=MENU(1):MENU
    ON menuitem GOSUB Blank,invert,Flash,Demo,Quit
    Setmenubar:
        MENU RESET  ' Re-do menu bar
        MENU 6,0,1,"Program Menu"
        MENU 6,1,1,"Blank Screen"
        MENU 6,2,1,"Invert Screen"
        MENU 6,3,1,"Flash Screen"
        MENU 6,4,1,"Demo"
        MENU 6,5,1,"Quit"
RETURN
Blank:
HIDECURSOR
CALL BlankScreen(mem%)
SHOWCURSOR
RETURN

invert:
HIDECURSOR
CALL invertScreen(mem%)
SHOWCURSOR
RETURN

Flash:
HIDECURSOR
FOR i=0 TO 100
CALL invertScreen(mem%)
NEXT
SHOWCURSOR
RETURN

Demo:
WINDOW CLOSE 1
GOSUB Blank
WINDOW 1,"",(42,90)-(475,300),3
PRINT "Click here"
WHILE MOUSE(0)<>1:WEND
GOSUB invert
WHILE MOUSE(0)<>1:WEND
GOSUB invert:CLS:GOSUB invert
WINDOW 2,"",(102,140)-(410,240),3
PRINT "Click here"
WHILE MOUSE(0)<>1:WEND
GOSUB invert
WHILE MOUSE(0)<>1:WEND
GOSUB invert:CLS:GOSUB invert
WINDOW 3,"",(152,165)-(360,215),3
PRINT "Click here"
WHILE MOUSE(0)<>1:WEND
GOSUB invert
WHILE MOUSE(0)<>1:WEND
GOSUB invert:CLS:GOSUB invert
GOSUB invert
PRINT SPC(4);"Please make selection":PRINT SPC(5);"from menus above!"
RETURN

Quit:
FOR i=1 TO 4
    WINDOW CLOSE i
NEXT i
MENU RESET:LIBRARY CLOSE
CLS:END