;tabs every 8
;
;SetLace implementation by Bryce Nesbitt, based on an example by Bob
;Pariseau of C-A. Public Domain.
;
;On most monitors a non-interlaced display will leave black bars between
;each scan line.  This is evident in all the 200 line display modes of the
;Amiga 1000.  For photographs or longer persistence displays this black is
;undesirable.  SetLace instructs the system to set interlace; on each
;successive field the same display data will be painted in between that of 
;the previous field.  This may be a necessity for use of the Amiga with
;some NTSC video gear and broadcast television equipment.  For most computer
;(non-broadcast) applications interlace will flicker unacceptably unless
;the contrast, brightness and room lighting are all turned way down.
;
;CLI Syntax:   SetLace      ;Flip (XOR) interlace
;      SetLace 1   ;Turn lace on
;      SetLace 0   ;Turn lace off
;Workbench:         ;Flip (XOR)
;ALL screens will be forced to interlace
;
;Author correspondence, bug or stupidity reports may be directed to:
;   Bryce Nesbitt
;   1712 Marin Ave.
;   Berkeley, Ca 94707-2902
*************************

_AbsExecBase equ 4

_LVOForbid equ -$84
_LVOPermit equ -$8a
_LVOGetMsg equ -$174
_LVOReplyMsg equ -$17a
_LVOWaitPort equ -$180
_LVOCloseLibrary equ -$19e
_LVOOpenLibrary equ -$228

_LVORemakeDisplay equ -$180

INTERLACE equ 4

pr_Result2 equ $94
pr_CLI equ $ac
pr_MsgPort equ $5c
gb_system_bplcon0 equ $a4
ThisTask equ $114

jsrlib   macro
   jsr   _LVO\1(a6)
   endm
jmplib   macro
   jmp   _LVO\1(a6)
   endm
**************************
      CODE
startup:   move.l   a0,a4      ;CLI line pointer
      move.l   d0,d4      ;CLI line length

       movea.l _AbsExecBase,a6   test if WB or CLI
       movea.l ThisTask(a6),a5
       moveq   #0,d0
       tst.l   pr_CLI(a5)
       bne.s   fromCLI      ;If not zero, then save a zero...
;
; If called from Workbench a message will be sent.  This waits for it,
;  and saves it's pointer to be returned to Workbench later.
;
      lea   pr_MsgPort(a5),a0
      jsrlib   WaitPort
      lea   pr_MsgPort(a5),a0
      jsrlib   GetMsg      ;Message pointer in D0
      moveq   #0,d4      ;clear CLI line pointer
fromCLI    move.l   d0,-(a7)   ;Save message for later...


******************************** [A6=ExecBase][a5=this task][a4=CLI line]
* [d4=CLI length]
returncode   equr   d7
ibase      equr   d6
gbase      equr   d5
* (d4,a4,a5)

      moveq   #20,returncode   ;default to 'severe failure' code
      lea   IntuiName(pc),a1
      moveq   #0,d0
      jsrlib   OpenLibrary
      move.l   d0,ibase    ;Error check. What a pain! Could we
      beq.s   e_Intui       ;not agree that Intuition and a few
      lea   Graphname(pc),a1 ;other core libraries will always
      moveq   #0,d0       ;be openable??
      jsrlib   OpenLibrary
      move.l   d0,gbase
      beq.s   e_Graph
;
;Modifying the system-wide bplcon0.  From here we can change all screens
;to INTERLACE and turn tricks like disabling colorburst.  The Forbid/
;Permit pair is used for saftey while modifying this stuff.
;
      jsrlib   Forbid
      move.l   gbase,a6   ;gbase

      subq.l   #2,d4      ;0=wb 1=cli no args 2=1 arg
      bmi.s   flip      ;wb, or cli flip
      bne.s   toomanychars
      cmpi.b   #'0',(a4)
      beq.s   clear
      cmpi.b   #'1',(a4)
      bne.s   badargs

setlace      ori.w   #INTERLACE,gb_system_bplcon0(a6)   ;Set lace
      bra.s   break
clear      andi.w   #$ffff-INTERLACE,gb_system_bplcon0(a6)   ;Clear lace
      bra.s   break
flip      eori.w   #INTERLACE,gb_system_bplcon0(a6)    ;Flip lace

break      move.l   ibase,a6
      jsrlib   RemakeDisplay   ;The big one! Rethink ALL displays
      moveq   #0,returncode   ;Everything is OK!
      bra.s   goodexit
badargs
toomanychars   move.l   #120,pr_Result2(a5) ;'arg line invalid or too long'
      moveq   #10,d7      ;return code 10, less serious error
goodexit   move.l   4,a6
      jsrlib   Permit
;
;RemakeDisplay() is spec'ed to do a Forbid() and then Permit() around it's
; lengthy operation. This is just a saftey valve in case it did not...
;
      move.l   gbase,a1
      jsrlib   CloseLibrary
e_Graph      move.l   ibase,a1
      jsrlib   CloseLibrary
e_Intui
******************************** (a7)+=message d7=return code
ExitToDOS   move.l   (a7)+,d6
      beq.s   NotWB   ;If saved pointer is zero, exit to CLI...
;
; Return the startup message to the parent Workbench tool. The forbid
; is needed so workbench can't UnLoadSeg() the code too early.
;

       movea.l _AbsExecBase,a6
       jsrlib  Forbid       reply to WB
       movea.l d6,a1
       jsrlib  ReplyMsg
       jsrlib  Permit

NotWB  move.l   d7,d0      ;Set "failat" code
       rts
IntuiName   dc.b   'intuition.library',0
Graphname   dc.b  'graphics.library',0
MyName      dc.b 'Bryce Nesbitt'
;-- this is the end --
     end