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sms/vdp: implement "chrsel" hook

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This allows for outputting a character selection before it's given
through GetC. That allows a pad-oriented character selection scheme.
This commit is contained in:
Virgil Dupras 2019-07-02 13:14:02 -04:00
parent 74de1c92cf
commit 2679172edf
1 changed files with 72 additions and 13 deletions
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85
kernel/sms/vdp.asm
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@ -16,9 +16,14 @@
; *** Variables ***
;
; Row of cursor
.equ VDP_ROW VDP_RAMSTART
; Line of cursor
.equ VDP_LINE VDP_ROW+1
.equ VDP_RAMEND VDP_LINE+1
; Returns, in A, the currently selected char. Sets Z if unchanged, unset if
; changed.
.equ VDP_CHRSELHOOK VDP_LINE+1
.equ VDP_RAMEND VDP_CHRSELHOOK+2
; *** Code ***
@ -26,6 +31,8 @@ vdpInit:
xor a
ld (VDP_ROW), a
ld (VDP_LINE), a
ld hl, noop
ld (VDP_CHRSELHOOK), hl
ld hl, vdpInitData
ld b, vdpInitDataEnd-vdpInitData
@ -75,18 +82,10 @@ vdpInit:
out (VDP_CTLPORT), a
ret
vdpPutC:
; First, let's place our cursor. We need to first send our LSB, whose
; 6 low bits contain our row*2 (each tile is 2 bytes wide) and high
; 2 bits are the two low bits of our line
; special case: line feed, carriage return
cp ASCII_LF
jr z, vdpLF
cp ASCII_CR
jr z, vdpCR
; ... but first, let's convert it.
call vdpConv
; ... and store it away
; Spits char set in A at current cursor position. Doesn't move the cursor.
; A is a "sega" char
vdpSpitC:
; store A away
ex af, af'
push bc
ld b, 0 ; we push rotated bits from VDP_LINE into B so
@ -113,6 +112,25 @@ vdpPutC:
; We're ready to send our data now. Let's go
ex af, af'
out (VDP_DATAPORT), a
ret
vdpPutC:
; First, let's place our cursor. We need to first send our LSB, whose
; 6 low bits contain our row*2 (each tile is 2 bytes wide) and high
; 2 bits are the two low bits of our line
; special case: line feed, carriage return, back space
cp ASCII_LF
jr z, vdpLF
cp ASCII_CR
jr z, vdpCR
cp ASCII_BS
jr z, vdpBS
; ... but first, let's convert it.
call vdpConv
; and spit it on screen
call vdpSpitC
; Move cursor. The screen is 32x24
ex af, af'
@ -150,6 +168,31 @@ vdpLF:
pop af
ret
vdpBS:
push af
ld a, (VDP_ROW)
or a
jr z, .lineup
dec a
ld (VDP_ROW), a
pop af
ret
.lineup:
; end of line
ld a, 31
ld (VDP_ROW), a
; we have to go one line up
ld a, (VDP_LINE)
or a
jr z, .nowrap
; We have to wrap to the bottom of the screen
ld a, 24
.nowrap:
dec a
ld (VDP_LINE), a
pop af
ret
; Convert ASCII char in A into a tile index corresponding to that character.
; When a character is unknown, returns 0x5e (a '~' char).
vdpConv:
@ -161,6 +204,22 @@ vdpConv:
ld a, 0x5e
ret
; During the shell loop, updates the currently selected char, if appropriate
vdpShellLoopHook:
push af
push ix
xor a
ld ix, (VDP_CHRSELHOOK)
call callIX
jr z, .noChange
; selection changed
call vdpConv
call vdpSpitC
.noChange:
pop ix
pop af
ret
vdpPaletteData:
.db 0x00,0x3f
vdpPaletteDataEnd: