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
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
|
;
; Christian Groessler, June 2004
;
; void __fastcall__ _scroll (signed char numlines);
; numlines > 0 scrolls up
; numlines < 0 scrolls down
;
.include "atari.inc"
.importzp tmp1,tmp4,ptr1,ptr2
.import _mul40,_clrscr
.export __scroll
.proc __scroll
cmp #0
beq jmpfin
; cmp #$80
; bcc up
bpl up
;scroll down
eor #$ff
clc
adc #1 ; make positive
sta tmp1
cmp #24 ; scroll >= the whole screen?
bcc down_ok
jmp _clrscr
down_ok:lda SAVMSC
clc
adc #<(40*23)
sta ptr1
sta ptr2
lda SAVMSC+1
adc #>(40*23)
sta ptr1+1 ; point to last line on screen
sta ptr2+1
lda tmp1
jsr _mul40
sta tmp4
lda ptr2
sec
sbc tmp4
sta ptr2
stx tmp4
lda ptr2+1
sbc tmp4
sta ptr2+1
lda #24 ; # of lines on screen
sec
sbc tmp1 ; # of lines to move
tax
;very simple, could be improved
scrold: ldy #39 ; # of chars on a line - 1
copy_d: lda (ptr2),y
sta (ptr1),y
dey
bpl copy_d
lda ptr1
sec
sbc #40
sta ptr1
bcs u1
dec ptr1+1
u1: lda ptr2
sec
sbc #40
sta ptr2
bcs u2
dec ptr2+1
u2: dex
bne scrold
; fill new scrolled in lines with space
ldx tmp1 ; # of new lines
fild: lda #0
ldy #39
fill_d: sta (ptr1),y
dey
bpl fill_d
dex
jmpfin: beq finish
lda ptr1
sec
sbc #40
sta ptr1
bcs u3
dec ptr1+1
u3: jmp fild
;scroll up
up: sta tmp1 ; # of lines to scroll
cmp #24 ; scroll >= the whole screen?
bcc up_ok
jmp _clrscr
;multiply by 40 (xsize)
up_ok: jsr _mul40 ; carry is cleared by _mul40
adc SAVMSC ; add start of screen mem
sta ptr2
txa
adc SAVMSC+1
sta ptr2+1
lda SAVMSC+1
sta ptr1+1
lda SAVMSC
sta ptr1
lda #24 ; # of lines on screen
sec
sbc tmp1 ; # of lines to move
tax
;very simple, could be improved
scroll: ldy #39 ; # of chars on a line - 1
copy_l: lda (ptr2),y
sta (ptr1),y
dey
bpl copy_l
lda #40
clc
adc ptr1
sta ptr1
bcc l1
inc ptr1+1
l1: lda #40
clc
adc ptr2
sta ptr2
bcc l2
inc ptr2+1
l2: dex
bne scroll
; fill new scrolled in lines with space
ldx tmp1 ; # of new lines
fill: lda #0
ldy #39
fill_l: sta (ptr1),y
dey
bpl fill_l
dex
beq finish
lda #40
clc
adc ptr1
sta ptr1
bcc l3
inc ptr1+1
l3: jmp fill
finish: rts
.endproc
|
