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;
; Ullrich von Bassewitz, 06.08.1998
;
; void cputcxy (unsigned char x, unsigned char y, char c);
; void cputc (char c);
;
.export _cputcxy, _cputc, cputdirect, putchar
.export newline, plot
.import gotoxy
.import PLOT
.scope KERNAL
.include "cbm_kernal.inc"
.endscope
.include "vic20.inc"
; VIC-20 KERNAL routines (such as PLOT) do not always leave the color RAM
; pointer CRAM_PTR pointing at the color RAM location matching the screen
; RAM pointer SCREEN_PTR. Instead they update it when they need it to be
; correct by calling UPDCRAMPTR.
;
; We make things more efficient by having conio always update CRAM_PTR when
; we move the screen pointer to avoid extra calls to ensure it's updated
; before doing screen output. (Among other things, We replace the ROM
; version of PLOT with our own in libsrc/vic20/kplot.s to ensure this
; precondition.)
;
; However, this means that CRAM_PTR may be (and is, after a cold boot)
; incorrect for us at program startup, causing cputc() not to work. We fix
; this with a constructor that ensures CRAM_PTR matches SCREEN_PTR.
;
UPDCRAMPTR := KERNAL::UPDCRAMPTR ; .constructor doesn't understand namespaces
.constructor UPDCRAMPTR
_cputcxy:
pha ; Save C
jsr gotoxy ; Set cursor, drop x and y
pla ; Restore C
; Plot a character - also used as internal function
_cputc: cmp #$0A ; CR?
bne L1
lda #0
sta CURS_X
beq plot ; Recalculate pointers
L1: cmp #$0D ; LF?
beq newline ; Recalculate pointers
; Printable char of some sort
cmp #' '
bcc cputdirect ; Other control char
tay
bmi L10
cmp #$60
bcc L2
and #$DF
bne cputdirect ; Branch always
L2: and #$3F
cputdirect:
jsr putchar ; Write the character to the screen
; Advance cursor position
advance:
iny
cpy #XSIZE
bne L3
jsr newline ; new line
ldy #0 ; + cr
L3: sty CURS_X
rts
newline:
clc
lda #XSIZE
adc SCREEN_PTR
sta SCREEN_PTR
bcc L4
inc SCREEN_PTR+1
clc
L4: lda #XSIZE
adc CRAM_PTR
sta CRAM_PTR
bcc L5
inc CRAM_PTR+1
L5: inc CURS_Y
rts
; Handle character if high bit set
L10: and #$7F
cmp #$7E ; PI?
bne L11
lda #$5E ; Load screen code for PI
bne cputdirect
L11: ora #$40
bne cputdirect
; Set cursor position, calculate RAM pointers
plot: ldy CURS_X
ldx CURS_Y
clc
jmp PLOT ; Set the new cursor
; Write one character to the screen without doing anything else, return X
; position in Y
putchar:
ora RVS ; Set revers bit
ldy CURS_X
sta (SCREEN_PTR),y ; Set char
lda CHARCOLOR
sta (CRAM_PTR),y ; Set color
rts
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