TITLE   "mp3.a solved by Douglas Jones"

        S       START
        USE     "hawk.macs"
        USE     "monitor.h"

        COMMON  STACK,#1000
PSTACK: W       STACK

; ----------------- linkage ------------------

; these lines provide a link to the data structures from mp1
        EXT     ITEM1
PITEM1: W       ITEM1

; these lines provide a link to the code in mp3test.o
        EXT     PLOTROW
        EXT     PLOTSTR
PPLOTROW:
        W       PLOTROW
PPLOTSTR:
        W       PLOTSTR

; -------- the structure of one item ---------

NEXT    =       0       ; pointer to next item in list
X       =       4       ; X coordinate of this item
Y       =       8       ; Y coordinate of this item
WIDTH   =       12      ; width of this item
HEIGHT  =       16      ; height of this item
TEXT    =       20      ; pointer to text of this item or null

NULL    =       0       ; value of null pointers

        SUBTITLE "main program"
; --------------------------------------------
START:
        LOAD    R2,PSTACK       ; set up the stack

        LOAD    R1,PDSPINI
        JSRS    R1,R1           ; initialize the display

        LOAD    R8,PITEM1       ; p = pitem1, points to start of list

MAINLP:                         ; for (;;) {
        TESTR   R8
        BZS     MAINQ           ;   if (p == NULL) exit

        MOVE    R3,R8           ;   parameter p
        JSR     R1,SHOWITEM     ;   call showitem( p )
        
        LOADS   R8,R8           ;   p = p->next
        BR      MAINLP          ; }
MAINQ:

        LOAD    R1,PEXIT
        JSRS    R1,R1           ; call monitor routine to stop!

        SUBTITLE "showitem"
; --------------------------------------------
RETAD   =       0
R8SAVE  =       4
R9SAVE  =       8
RASAVE  =       12
ARSIZE  =       16

SHOWITEM:
        ; expects R3 = item pointer
        STORES  R1,R2
        STORE   R8,R2,R8SAVE
        MOVE    R8,R3           ; R8 = item pointer in SHOWITEM body
        LOAD    R9,R8,HEIGHT    ; R9 = rows = item.height
        LOAD    R10,R8,Y        ; R10 = y = item.y

        LOAD    R3,R8,X         ; -- parameter x = item.x
        MOVE    R4,R10          ; -- parameter y = y
        LOAD    R5,R8,WIDTH     ; -- parameter w = item.width
        LIS     R6,'+'          ; -- parameter   = '+'
        LIS     R7,'-'          ; -- parameter   = '-'
        ADDI    R2,R2,ARSIZE
        LOAD    R1,PPLOTROW
        JSRS    R1,R1           ; plotrow( x, y, w,'+','-')
        ADDI    R2,R2,-ARSIZE

        TESTR   R9
        BLE     SHOWITEMENDIF   ; if (rows > 0) {

SHOWITEMLP:
        CMPI    R9,1
        BLE     SHOWITEMENDLP   ;   while (rows > 1) {

        ADDSI   R10,1           ;     y = y + 1
        ADDSI   R9,-1           ;     rows = rows - 1

        LOAD    R3,R8,X         ;     -- parameter x = item.x
        MOVE    R4,R10          ;     -- parameter y = y
        LOAD    R5,R8,WIDTH     ;     -- parameter w = item.width
        LIS     R6,'|'          ;     -- parameter   = '|'
        LIS     R7,' '          ;     -- parameter   = ' '
        ADDI    R2,R2,ARSIZE
        LOAD    R1,PPLOTROW
        JSRS    R1,R1           ;     plotrow( x, y, w,'|',' ')
        ADDI    R2,R2,-ARSIZE

        BR      SHOWITEMLP      ;   }
SHOWITEMENDLP:

        ADDSI   R10,1           ;   y = y + 1

        LOAD    R3,R8,X         ;   -- parameter x = item.x
        MOVE    R4,R10          ;   -- parameter y = y
        LOAD    R5,R8,WIDTH     ;   -- parameter w = item.width
        LIS     R6,'+'          ;   -- parameter   = '+'
        LIS     R7,'-'          ;   -- parameter   = '-'
        ADDI    R2,R2,ARSIZE
        LOAD    R1,PPLOTROW
        JSRS    R1,R1           ;   plotrow( x, y, w,'+','-')
        ADDI    R2,R2,-ARSIZE

SHOWITEMENDIF:                  ; }

        LOADCC  R3,R8,TEXT
        BZS     SHOWITEMBLANK   ; if (item.text != NULL) {

        LOAD    R3,R8,X
        ADDI    R3,R3,2         ;   -- parameter x = item.x + 2
        LOAD    R4,R8,Y
        ADDI    R4,R4,1         ;   -- parameter y = item.y + 1
        LOAD    R5,R8,TEXT      ;   -- parameter
        ADDI    R2,R2,ARSIZE
        LOAD    R1,PPLOTSTR
        JSRS    R1,R1           ;   call plotstr( x, y, text )
        ADDI    R2,R2,-ARSIZE

SHOWITEMBLANK:                  ; }

        LOAD    R8,R2,R8SAVE
        LOAD    R9,R2,R9SAVE
        LOAD    R10,R2,RASAVE
        LOADS   R1,R2
        JUMPS   R1              ; return

        END