4cade/src/ui.font.a

;license:MIT
;(c) 2018-9 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 glue.font
; which handle bank switching for you.
;
; Public functions
; - DrawPageInternal
; - Draw40CharsInternal
; - DrawCenteredStringInternal
; - DrawStringInternal
; - DrawBufferInternal
;

DrawPageInternal
; A/Y contains address of character buffer
; carry bit clear -> draw on page 1
; carry bit set   -> draw on page 2
; drawing starts at VTAB 0, HTAB 0
; clobbers PTR
; clobbers A/X/Y
; preserves all flags, by a quirk of implementation
         php
         ldx   #0
         stx   VTAB
         +STAY PTR
@drawLine
         ldy   #0
         sty   HTAB
@parseLine
         lda   (PTR),y
         cmp   #$5B                  ; '[' at beginning on line
         bne   +                     ; ends the parsing
         tya
         beq   @donePage
+        cmp   #$0D
         beq   @doneParsingLine
         cmp   #$2A
         bne   +
         lda   #$10
         sta   (PTR),y               ; asterisk -> dot, small
+        cmp   #$7E
         bne   +
         lda   #$11
         sta   (PTR),y               ; tilde -> dot, medium
+        iny
         bne   @parseLine
@doneParsingLine
         sty   SAVE
         cpy   #0
         beq   @skip
         ldx   SAVE
         +LDAY 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
; 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
         +STAY PTR

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

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
         +STAY PTR

         ldy   #0
+        lda   (PTR),y
         tax
         inc   PTR
         bne   +
         inc   PTR+1
+
         +LDAY PTR
; note: execution falls through here

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
         +STAY @src+1
         bcs   +
         lda   #$00
         +HIDE_NEXT_2_BYTES
+
         lda   #$60
         sta   @pagemask
         dex
         lda   VTAB
         asl
         asl
         asl
; routine to calculate memory address within HGR page
; and self-modify addresses within draw loop that follows
; (routine clobbers A and Y but preserves X)
         asl
         tay
         and   #$F0
         bpl   @calc1
         ora   #$05
@calc1   bcc   @calc2
         ora   #$0A
@calc2   asl
         asl
         sta   @hgrlo+1
         tya
         and   #$0E
         adc   #$10
         asl   @hgrlo+1
         rol
@pagemask=*+1
         eor   #$FD                  ; SMC (0=hi-res page 1, #$60=hi-res page 2)
         sta   @row0+2
         clc
         adc   #$04
         sta   @row1+2
         adc   #$04
         sta   @row2+2
         adc   #$04
         sta   @row3+2
         adc   #$04
         sta   @row4+2
         adc   #$04
         sta   @row5+2
         adc   #$04
         sta   @row6+2
         adc   #$04
         sta   @row7+2
@hgrlo   lda   #$FD
         clc
         adc   HTAB
         sta   @row0+1
         sta   @row1+1
         sta   @row2+1
         sta   @row3+1
         sta   @row4+1
         sta   @row5+1
         sta   @row6+1
         sta   @row7+1
@loop
@src     ldy   $FDFD,x
         lda   FontDataRow0,y
@row0    sta   $FDFD,x
         lda   FontDataRow1,y
@row1    sta   $FDFD,x
         lda   FontDataRow2,y
@row2    sta   $FDFD,x
         lda   FontDataRow3,y
@row3    sta   $FDFD,x
         lda   FontDataRow4,y
@row4    sta   $FDFD,x
         lda   FontDataRow5,y
@row5    sta   $FDFD,x
         lda   FontDataRow6,y
@row6    sta   $FDFD,x
         lda   FontDataRow7,y
@row7    sta   $FDFD,x
         inc   HTAB
         dex
         bpl   @loop
         rts