83Plus:Hooks:9B9C
Contents
Synopsis
Name: Font Hook
Hook Pointer Block Address: 9B9C
Hook Enable BCALL: 4FE4
Hook Disable BCALL: 4FE7
Hook Call BCALL: 4003
Hook Active Flag: 5, (iy + 35h)
This hook allows you to change the font bitmaps; for example, it is used for Omnicalc's custom fonts.
Using the Hook
This hook is called when a character is about to be displayed. A = 0 for small font, 1 for large font. B contains the character. If you want to use the default characters (or rather, the bitmaps provided by the localize hook), return with zero reset. If you do this, HL must be left intact. Otherwise, set HL pointing to the font data, which must be in RAM. If you want to, you can copy data to sFont_record and lFont_record, and then point HL to this location. Of course, you can use any location you want.
- In small font:
(HL) = width of character (HL+1) = first (accent) row, right aligned (the last pixel usually clear) (HL+2) = second row ... (HL+6) = sixth row (HL+7) = seventh row (only displayed with bit textEraseBelow, (iy+textFlags) set)
- In large font:
(HL) = first row, right aligned ... (HL+6) = seventh row
See the example code for actual formatted data.
Comments
This hook is one of the four "official" hooks defined in ti83plus.inc.
Example
The following code displays the letter A in boldface:
FontHook: .db 83h ; Required for all hooks or a ; is it small or large font? jr z,SmallFont ld a,b ; what character is to be displayed? cp 'A' ret nz ld hl,BigA ; get our replacement bitmap ld de,lFont_record ld bc,7 ; copy it into RAM ldir ld hl,lFont_record cp a ret SmallFont: ld a,b ; what character is to be displayed? cp 'A' ret nz ld hl,SmallA ; get our replacement bitmap ld de,sFont_record ld bc,8 ; copy it into RAM ldir ld hl,sFont_record cp a ret BigA: .db 00001110b .db 00010011b .db 00010011b .db 00011111b .db 00010011b .db 00010011b .db 00010011b SmallA: .db 5 .db 00000000b .db 00001100b .db 00010110b .db 00011110b .db 00010110b .db 00010110b .db 00000000b