4cade/src/ui.font.lc2.a

;license:MIT
;(c) 2018-2020 by 4am
;
; hi-res font drawing routines
;
; /!\ These live in LC RAM 2 and rely on the font data which is also in LC RAM 2. /!\
; Code in LC RAM 1 (which is most program code) should call the functions in ui.font
; which handle bank switching for you.
;

DrawPageInternal
; A/Y contains address of character buffer
; X contains 0-indexed left margin (HTAB)
; carry bit clear -> draw on page 1
; carry bit set   -> draw on page 2
; drawing starts at VTAB 0
; each line starts at column X which was passed in (0-indexed)
; clobbers PTR
; clobbers $FF
; clobbers A/X/Y
; preserves all flags, by a quirk of implementation
         php
         stx   $FF
         ldx   #0
         stx   VTAB
         +ST16 PTR
@drawLine
         lda   $FF
         sta   HTAB
         ldy   #0
@parseLine
         lda   (PTR), y
         beq   @donePage
         cmp   #$0A
         beq   @doneParsingLine
         iny
         bne   @parseLine
@doneParsingLine
         sty   SAVE
         tya
         beq   @skip
         ldx   SAVE
         +LD16 PTR
         plp
         php
         jsr   DrawBufferInternal
@skip    inc   SAVE                  ; skip carriage return
         lda   SAVE                  ; advance PTR to start of next line
         clc
         adc   PTR
         sta   PTR
         bcc   +
         inc   PTR+1
+        inc   VTAB                  ; this will print 255 lines if you give it
         bne   @drawLine             ; 255 lines, so don't do that
@donePage
         plp
         rts

Draw40CharsInternal
; A/Y contains address of character buffer
; carry bit clear -> draw on page 1
;v carry bit set   -> draw on page 2
; $25 contains textpage line (0..23) (this is the standard VTAB address)
; drawing starts at HTAB 0
; increments VTAB
; sets HTAB to 0 on exit
; clobbers A/X/Y
         jsr   +
         ldx   #40
         jsr   DrawBufferInternal
         inc   VTAB
+        ldx   #0
         stx   HTAB
         rts

DrawCenteredStringInternal
; A/Y contains address of length-prefixed string
; carry bit clear -> draw on page 1
; carry bit set   -> draw on page 2
; $25 contains textpage line (0..23) (this is the standard VTAB address)
; clobbers A/X/Y
; clobbers PTR/PTR+1
         +ST16 PTR

         ldy   #0
         php
         lda   #40
         sec
         sbc   (PTR),y
         lsr
         sta   HTAB
         plp
         beq   +

DrawStringInternal
; A/Y contains address of length-prefixed string
; carry bit clear -> draw on page 1
; carry bit set   -> draw on page 2
; $24 contains starting column (0..39) (this is the standard HTAB address)
; $25 contains textpage line (0..23) (this is the standard VTAB address)
; clobbers A/X/Y
; clobbers PTR/PTR+1
         +ST16 PTR

         ldy   #0
+        lda   (PTR),y
         tax
         inc   PTR
         bne   +
         inc   PTR+1
+
         +LD16 PTR
         ; /!\ execution falls through here to DrawBufferInternal

DrawBufferInternal
; A/Y contains address of character buffer
; X contains buffer length (1..40)
; carry bit clear -> draw on page 1
; carry bit set   -> draw on page 2
; characters MUST have high bit off (0x00..0x7F)
; special characters (0x00..0x1F) will be drawn
; $24 contains starting column (0..39) (this is the standard HTAB address)
; $25 contains textpage line (0..23) (this is the standard VTAB address)
; all characters are drawn on the same line
; HTAB is incremented for each character
; VTAB is NOT incremented
; clobbers A/X/Y
         +ST16 DBISrc+1
         php
         dex
         lda   VTAB
         asl
         asl
         asl
; routine to calculate memory address within HGR page
; and self-modify addresses within draw loop that follows
; (routine clobbers A and Y but preserves X)
         asl
         tay
         and   #$F0
         bpl   @calc1
         ora   #$05
@calc1   bcc   @calc2
         ora   #$0A
@calc2   asl
         asl
         sta   @hgrlo+1
         tya
         and   #$0E
         adc   #$10
         asl   @hgrlo+1
         rol
         plp
         bcc   +
         eor   #$60
         clc
+
         sta   DBIRow0+2
         adc   #$04
         sta   DBIRow1+2
         adc   #$04
         sta   DBIRow2+2
         adc   #$04
         sta   DBIRow3+2
         adc   #$04
         sta   DBIRow4+2
         adc   #$04
         sta   DBIRow5+2
         adc   #$04
         sta   DBIRow6+2
         adc   #$04
         sta   DBIRow7+2
@hgrlo   lda   #$FD
         clc
         adc   HTAB
         sta   DBIRow0+1
         sta   DBIRow1+1
         sta   DBIRow2+1
         sta   DBIRow3+1
         sta   DBIRow4+1
         sta   DBIRow5+1
         sta   DBIRow6+1
         sta   DBIRow7+1
DBILoop
DBISrc   ldy   $FDFD,x
         lda   FontDataRow0,y
DBIRow0  sta   $FDFD,x
         lda   FontDataRow1,y
DBIRow1  sta   $FDFD,x
         lda   FontDataRow2,y
DBIRow2  sta   $FDFD,x
         lda   FontDataRow3,y
DBIRow3  sta   $FDFD,x
         lda   FontDataRow4,y
DBIRow4  sta   $FDFD,x
         lda   FontDataRow5,y
DBIRow5  sta   $FDFD,x
         lda   FontDataRow6,y
DBIRow6  sta   $FDFD,x
         lda   FontDataRow7,y
DBIRow7  sta   $FDFD,x
         inc   HTAB
         dex
         bpl   DBILoop
         rts