.include "atari.inc"
 .export _clrtobot, _clrtoeol, _clrtoline, _cspaces, _cblank, _backspace

 .import mul40        ; from cc65's runtime
 .importzp tmp3       ; ditto
 .import bump_destptr ; these two are
 .importzp destptr    ; from draw_lorcha.s
 .import _cspace

 .ifdef CART_TARGET
  .segment "HIGHCODE"
 .else
  .code
 .endif


; void clrtobot(void);
; void clrtoeol(void);
; void clrtoline(unsigned char line);

; this stuff doesn't disturb conio's (and the OS's) idea of the
; current cursor position. It's *way* faster than writing them in
; C in terms of cclear() (which uses one cputc() call per blank).

_clrtobot: ; same as clrtoline(24);
 lda #24
 bne _clrtoline

_clrtoeol:
 lda ROWCRS
 ; fall through to _clrtoline

_clrtoline:
 sta tmp3 ; stash our arg
 lda #0
 sta OLDCHR ; stop conio from redrawing stuff after we clear it

 ; setup destptr to start of current line, NOT
 ; current cursor position.
 lda ROWCRS
 jsr mul40  ; AX = A*40 (addr of start-of-row)
 clc
 adc SAVMSC ; add to screen pointer
 sta destptr
 txa
 adc SAVMSC+1
 sta destptr+1

 ; X = current row, Y = current column. Stop clearing a line when Y == 40,
 ; we're done when X == 24. Apologies, the names X and Y are backwards
 ; compared to proper Cartesian coordinates.
 ldx ROWCRS
 ldy COLCRS
 lda #0

clrloop:
 sta (destptr),y ; blank a character (A == 0, screen code for a space)
 iny
 cpy #40
 bne clrloop
 ldy #0
 inx
 cpx tmp3
 bcs done

 jsr bump_destptr
 lda #0
 tay
 beq clrloop

done:
 rts

_cspaces:
 sta tmp3
@lp:
 jsr _cspace
 dec tmp3
 bne @lp
 rts

_cblank:
 tax
 lda COLCRS
 pha
 lda ROWCRS
 pha
 txa
 jsr _cspaces
 pla
 sta ROWCRS
 pla
 sta COLCRS
 rts

_backspace:
 dec COLCRS
 lda #1
 bne _cblank