blob: 0cfe2b91829c46b9d5f15498a7e0953ea56634bb (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
;; Clear the first nametable by resetting it to the default tile ID. This is a
;; rather drastic measure only to be done on examples that don't actually load
;; columns in "clever" ways, but they just want a clean slate.
.macro CLEAR_SCREEN
ldy #$20
jsr clear_screen_y
.endmacro
;; Clear the given two nametables. `ONE` and `OTHER` have to be the high byte
;; for each nametable to clear. For example, on an horizontal scrolling game:
;; `CLEAR_SCREENS $20, $24`.
.macro CLEAR_SCREENS ONE, OTHER
ldy #ONE
jsr clear_screen_y
ldy #OTHER
jsr clear_screen_y
.endmacro
;; Clear the nametable with the high byte as defined in the `y` register.
.proc clear_screen_y
bit $2002
lda #$00
ldx #$FF
@loop:
sty $2006
stx $2006
sta $2007
dex
bne @loop
iny
cpy #$24
bne @loop
rts
.endproc
|
