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ti/lcd: Add scrolling through z-offset

This commit is contained in:
Virgil Dupras 2019-11-09 08:25:10 -05:00
parent 6a70a0e5e6
commit 67f689260f

View File

@ -10,6 +10,22 @@
; Note that "X-increment" and "Y-increment" work in the opposite way than what
; most people expect. Y moves left and right, X moves up and down.
;
; *** Z-Offset ***
;
; This LCD has a "Z-Offset" parameter, allowing to offset rows on the
; screen however we wish. This is handy because it allows us to scroll more
; efficiently. Instead of having to copy the LCD ram around at each linefeed
; (or instead of having to maintain an in-memory buffer), we can use this
; feature.
;
; The Z-Offet goes upwards, with wrapping. For example, if we have an 8 pixels
; high line at row 0 and if our offset is 8, that line will go up 8 pixels,
; wrapping itself to the bottom of the screen.
;
; The principle is this: The active line is always the bottom one. Therefore,
; when active row is 0, Z is FNT_HEIGHT+1, when row is 1, Z is (FNT_HEIGHT+1)*2,
; When row is 8, Z is 0.
;
; *** Requirements ***
; fnt/mgm
;
@ -46,6 +62,10 @@ lcdInit:
; Clear screen
call lcdClrScr
; We begin with a Z offset of FNT_HEIGHT+1
ld a, LCD_CMD_ZOFFSET+FNT_HEIGHT+1
call lcdCmd
; Enable the LCD
ld a, LCD_CMD_ENABLE
call lcdCmd
@ -156,18 +176,24 @@ lcdSendGlyph:
lcdLinefeed:
push af
ld a, (LCD_CURROW)
add a, FNT_HEIGHT+1
cp 64
jr c, .nowrap ; A < 96? no wrap
; we have to wrap around to the top row
xor a
.nowrap:
call .addFntH
ld (LCD_CURROW), a
call lcdClrLn
; Now, lets set Z offset which is CURROW+FNT_HEIGHT+1
call .addFntH
add a, LCD_CMD_ZOFFSET
call lcdCmd
xor a
ld (LCD_CURCOL), a
pop af
ret
.addFntH:
add a, FNT_HEIGHT+1
cp 64
ret c ; A < 64? no wrap
; we have to wrap around
xor a
ret
; Clears B rows starting at row A
; B is not preserved by this routine