udemy_atari2600/y_coord_pos.dasm at main · DMinsky/udemy_atari2600 · GitHub

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
	processor 6502
	include "vcs.h"
	include "macro.h"

	seg.u variables
	org $80

PlayerHeight	equ 9
PlayerYPos	byte

	seg code
	org $f000

Start:
	sei
	cld
	ldx #$ff
	txs

	CLEAN_START
	lda #50
	sta PlayerYPos
	lda #$aa
	sta COLUBK

NextFrame:
	lda #2
	sta VSYNC
	sta VBLANK

	sta WSYNC
	sta WSYNC
	sta WSYNC
	lda #0
	sta VSYNC
	REPEAT 37
		sta WSYNC
	REPEND
	sta VBLANK

	ldy #192

Scanline:
	tya
	; Here we check if current scanline is "inside" the apple sprite rect
	; if it is we jump and draw the sprite
	; if not we use a "zero" line inside the apple bitmap data
	; and draw "an empty" sprite
	sec
	sbc PlayerYPos
	cmp PlayerHeight
	bcc DrawPlayer
	lda #0

DrawPlayer:
	tax
	lda Player,X
	sta GRP0
	lda PlayerColors,X
	sta COLUP0

	sta WSYNC

	dey
	bne Scanline

	lda #2
	sta VBLANK
	REPEAT 30
		sta WSYNC
	REPEND
	sta VBLANK

	jmp NextFrame

	org $ffea
Player:
	byte %00000000	;
	byte %00111100	;   ####
	byte %01111110	;  ######
	byte %11111111	; ########
	byte %11111111	; ########
	byte %11111111	; ########
	byte %01111110	;  ######
	byte %00010000	;    #
	byte %00111000	;   ###

PlayerColors:
	byte $40	; Red gradient
	byte $40	; Red gradient
	byte $42	;
	byte $44	;
	byte $44	;
	byte $48	;
	byte $48	;
	byte $ca	; Dark green
	byte $c4	; Dark green

	org $fffc
	.word Start
	.word Start