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collapseos/kernel/fnt/mgm.asm
Virgil Dupras a13a94bbc7 fix typos
2019-11-07 12:13:00 -05:00

33 lines
702 B
NASM

; Font management
;
; There can only ever be one active font.
;
; *** Defines ***
; FNT_DATA: Pointer to the beginning of the binary font data to work with.
; FNT_WIDTH: Width of the font.
; FNT_HEIGHT: Height of the font.
;
; *** Code ***
; If A is in the range 0x20-0x7e, make HL point to the beginning of the
; corresponding glyph and set Z to indicate success.
; If A isn't in the range, do nothing and unset Z.
fntGet:
cp 0x20
ret c ; A < 0x20. Z was unset by cp
cp 0x7f
jp nc, unsetZ ; A >= 0x7f. Z might be set
push af ; --> lvl 1
push bc ; --> lvl 2
sub 0x20
ld hl, FNT_DATA
ld b, FNT_HEIGHT
.loop:
call addHL
djnz .loop
pop bc ; <-- lvl 2
pop af ; <-- lvl 1
cp a ; set Z
ret