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
|
program SimpleBGScroll;
uses
ctypes, gba;
{$l build\r6502_portfont.bin.o}
{$include inc\r6502_portfont.bin.inc}
var
MAPADDRESS: pcuint16;
const
DELAY = 2; // slow things down
TILEWIDTH = 8; // how much to scroll
ROW = 10; // what row to place text at
// --------------------------------------------------------------------
var
palette: array [0..6] of cuint16;
// --------------------------------------------------------------------
const
message = ' ' +
'Hello, this is an example of an oldschool simple tile scroller ' +
'not unlike how it was done in days of yore. The ''@'' symbol ' +
'at the top of your screen is intentional, to dispel the illusion ' +
'of this scroller, to demonstrate the simple concept behind it. ' +
'Check out the source to learn how it works. It is very simple! ' +
'This exercise brought to you by r6502... ' +
'Text is about to restart... ';
procedure updatescrolltext(idx: cuint32);
var
i: integer;
temppointer: pcuint16;
begin
temppointer := pcuint16(MAPADDRESS + (ROW * 32));
// write out a whole row of text to the map
for i := 0 to 31 do
begin
// check for end of message so we can wrap around properly
if (message[idx] = #0) then
idx := 0;
// write a character - we subtract 32, because the font graphics
// start at tile 0, but our text is in ascii (starting at 32 and up)
// in other words, tile 0 is a space in our font, but in ascii a
// space is 32 so we must account for that difference between the two.
temppointer^ := Ord(message[idx]) - 32;
inc(temppointer);
inc(idx);
end;
end;
var
i, scrollx, scrolldelay, textindex: integer;
temppointer: pcuint16;
begin
MAPADDRESS := MAP_BASE_ADR(31); // our base map address
palette[0] := RGB8($40,$80,$c0);
palette[1] := RGB8($FF,$FF,$FF);
palette[2] := RGB8($F5,$FF,$FF);
palette[3] := RGB8($DF,$FF,$F2);
palette[4] := RGB8($CA,$FF,$E2);
palette[5] := RGB8($B7,$FD,$D8);
palette[6] := RGB8($2C,$4F,$8B);
// Set up the interrupt handlers
irqInit();
// Enable Vblank Interrupt to allow VblankIntrWait
irqEnable(IRQ_VBLANK);
// Allow Interrupts
REG_IME^ := 1;
// load the palette for the background, 7 colors
temppointer := BG_COLORS;
for i := 0 to 6 do
begin
temppointer^ := cuint32(palette[i]); // u32 cast avoids u8 memory writing
inc(temppointer);
end;
// load the font into gba video mem (48 characters, 4bit tiles)
CpuFastSet(@r6502_portfont_bin, pcuint16(VRAM), (r6502_portfont_bin_size div 4) or COPY32);
// clear screen map with tile 0 ('space' tile) (256x256 halfwords)
//MAP_BASE_ADR(31) := nil;
CpuFastSet( MAP_BASE_ADR(31), MAP_BASE_ADR(31), FILL or COPY32 or ($800 div 4));
// set screen H and V scroll positions
BG_OFFSET[0].x := 0;
BG_OFFSET[0].y := 0;
// initialize our variables
scrollx := 0;
textindex := 0;
scrolldelay := 0;
// put the '@' symbol on the top of the screen to show how
// the screen is only scrolling 7 pixels - to reveal the
// illusion of how the scroller works
pcuint16((MAPADDRESS + 1))^ := $20; // 0x20 == '@'
// draw a row of text from beginning of message
updatescrolltext(0);
// set the screen base to 31 (0x600F800) and char base to 0 (0x6000000)
BGCTRL[0] := SCREEN_BASE(31);
// screen mode & background to display
SetMode( MODE_0 or BG0_ON );
while true do
begin
VBlankIntrWait();
// check if we reached our delay
if (scrolldelay = DELAY) then
begin
// yes, the delay is complete, so let's reset it
scrolldelay := 0;
// check if we reached our scrollcount
if (scrollx = (TILEWIDTH-1)) then
begin
// yes, we've scrolled enough, so let's reset the count
scrollx := 0;
// check if we reached the end of our scrolltext
// and if so we need to restart our index
if (message[textindex] = #0) then
textindex := 0
else
inc(textindex);
// finally, let's update the scrolltext with the current text index
updatescrolltext(textindex);
end else
inc(scrollx);
end else
inc(scrolldelay);
// update the hardware horizontal scroll register
BG_OFFSET[0].x := scrollx;
end;
end.
|
