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sms/vdp: clear cursor before CR or BS

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This avoids having "ghost" chr selection sticking around.
This commit is contained in:
Virgil Dupras 2019-07-02 15:22:14 -04:00
parent ff7a114736
commit 9c87734499
1 changed files with 28 additions and 4 deletions
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32
kernel/sms/vdp.asm
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@ -20,10 +20,10 @@
.equ VDP_ROW VDP_RAMSTART
; Line of cursor
.equ VDP_LINE VDP_ROW+1
; Returns, in A, the currently selected char. Sets Z if unchanged, unset if
; changed.
; Returns, in A, the currently selected char in a "pad char selection" scheme.
.equ VDP_CHRSELHOOK VDP_LINE+1
.equ VDP_RAMEND VDP_CHRSELHOOK+2
.equ VDP_LASTSEL VDP_CHRSELHOOK+2
.equ VDP_RAMEND VDP_LASTSEL+1
; *** Code ***
@ -31,6 +31,7 @@ vdpInit:
xor a
ld (VDP_ROW), a
ld (VDP_LINE), a
ld (VDP_LASTSEL), a
ld hl, noop
ld (VDP_CHRSELHOOK), hl
@ -115,7 +116,13 @@ vdpSpitC:
ret
vdpPutC:
; First, let's place our cursor. We need to first send our LSB, whose
; First, let's invalidate last sel
ex af, af'
xor a
ld (VDP_LASTSEL), a
ex af, af'
; Then, 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
@ -149,6 +156,7 @@ vdpPutC:
jr vdpLF
vdpCR:
call vdpClrPos
push af
xor a
ld (VDP_ROW), a
@ -156,6 +164,9 @@ vdpCR:
ret
vdpLF:
; we don't call vdpClrPos on LF because we expect it to be preceded by
; a CR, which already cleared the pos. If we cleared it now, we would
; clear the first char of the line.
push af
ld a, (VDP_LINE)
inc a
@ -169,6 +180,7 @@ vdpLF:
ret
vdpBS:
call vdpClrPos
push af
ld a, (VDP_ROW)
or a
@ -193,6 +205,14 @@ vdpBS:
pop af
ret
; Clear tile under cursor
vdpClrPos:
push af
xor a ; space
call vdpSpitC
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:
@ -208,14 +228,18 @@ vdpConv:
vdpShellLoopHook:
push af
push ix
push hl
xor a
ld ix, (VDP_CHRSELHOOK)
call callIX
ld hl, VDP_LASTSEL
cp (hl)
jr z, .noChange
; selection changed
call vdpConv
call vdpSpitC
.noChange:
pop hl
pop ix
pop af
ret