circle.asm - Opengist

circle.asm · 3.0 KiB · NASM Bruto

; boot2.asm ; nasm -f bin boot2.asm -o boot2.img ; qemu-system-i386 -drive format=raw,file=boot2.img [org 0x7c00] bits 16 start: cli xor ax, ax mov ds, ax mov es, ax ; --- 1) 切换到 320×200 256 色模式 (mode 13h) --- mov ah, 0x00 mov al, 0x13 int 0x10 ; --- 2) 清屏（黑色） --- mov ax, 0xA000 mov es, ax xor di, di mov al, 0 mov cx, 320*200 rep stosb ; --- 3) 绘制灰色圆 --- call draw_circle jmp $ ; ------------------------------------------------------- ; draw_circle: 在 (160,100) 处以半径 80 画灰色圆 ; ------------------------------------------------------- draw_circle: mov cx, 80 ; radius = 80 xor dx, dx ; x = 0 mov bx, cx ; y = radius mov ax, 1 sub ax, cx ; d = 1 - radius circ_loop: ; 画出 8 个对称点 call plot_octants ; 更新决策变量 d ; temp = 4*x mov si, dx add si, si add si, si cmp ax, 0 jl d_negative ; d >= 0 mov di, bx add di, di add di, di ; di = 4*y sub si, di ; si = 4*(x - y) add si, 10 dec bx ; y-- jmp d_update d_negative: ; d < 0 add si, 6 d_update: add ax, si ; d += si inc dx ; x++ cmp dx, bx jle circ_loop ret ; ------------------------------------------------------- ; plot_octants: 将 (dx, bx) 对称的 8 点传入 plot_pixel ; 入口：DX=x, BX=y ; ------------------------------------------------------- plot_octants: ; 保存通用寄存 push ax push bx push cx push dx push si push di ; ( x, y) mov si, dx mov di, bx call plot_pixel ; ( y, x) mov si, bx mov di, dx call plot_pixel ; (-x, y) mov si, dx neg si mov di, bx call plot_pixel ; (-y, x) mov si, bx neg si mov di, dx call plot_pixel ; (-x, -y) mov si, dx neg si mov di, bx neg di call plot_pixel ; (-y, -x) mov si, bx neg si mov di, dx neg di call plot_pixel ; ( x, -y) mov si, dx mov di, bx neg di call plot_pixel ; ( y, -x) mov si, bx mov di, dx neg di call plot_pixel ; 恢复寄存 pop di pop si pop dx pop cx pop bx pop ax ret ; ------------------------------------------------------- ; plot_pixel: ; SI = x 偏移 (signed), DI = y 偏移 (signed) ; 在中心 (160,100) 上绘制一个灰色像素 (palette index = 7) ; ------------------------------------------------------- plot_pixel: push ax push bx push cx push dx ; 计算 px = 160 + SI, py = 100 + DI mov ax, 160 add ax, si ; px mov cx, 100 add cx, di ; py ; offset = py*320 + px = (py<<8)+(py<<6)+px mov bx, cx shl bx, 8 mov di, bx mov bx, cx shl bx, 6 add di, bx add di, ax mov al, 7 ; gray mov [es:di], al pop dx pop cx pop bx pop ax ret times 510-($-$$) db 0 dw 0xAA55

1	; boot2.asm
2	; nasm -f bin boot2.asm -o boot2.img
3	; qemu-system-i386 -drive format=raw,file=boot2.img
4
5	[org 0x7c00]
6	bits 16
7
8	start:
9	cli
10	xor ax, ax
11	mov ds, ax
12	mov es, ax
13
14	; --- 1) 切换到 320×200 256 色模式 (mode 13h) ---
15	mov ah, 0x00
16	mov al, 0x13
17	int 0x10
18
19	; --- 2) 清屏（黑色） ---
20	mov ax, 0xA000
21	mov es, ax
22	xor di, di
23	mov al, 0
24	mov cx, 320*200
25	rep stosb
26
27	; --- 3) 绘制灰色圆 ---
28	call draw_circle
29
30	jmp $
31
32	; -------------------------------------------------------
33	; draw_circle: 在 (160,100) 处以半径 80 画灰色圆
34	; -------------------------------------------------------
35	draw_circle:
36	mov cx, 80 ; radius = 80
37	xor dx, dx ; x = 0
38	mov bx, cx ; y = radius
39	mov ax, 1
40	sub ax, cx ; d = 1 - radius
41
42	circ_loop:
43	; 画出 8 个对称点
44	call plot_octants
45
46	; 更新决策变量 d
47	; temp = 4*x
48	mov si, dx
49	add si, si
50	add si, si
51
52	cmp ax, 0
53	jl d_negative
54	; d >= 0
55	mov di, bx
56	add di, di
57	add di, di ; di = 4*y
58	sub si, di ; si = 4*(x - y)
59	add si, 10
60	dec bx ; y--
61	jmp d_update
62
63	d_negative:
64	; d < 0
65	add si, 6
66
67	d_update:
68	add ax, si ; d += si
69	inc dx ; x++
70	cmp dx, bx
71	jle circ_loop
72	ret
73
74	; -------------------------------------------------------
75	; plot_octants: 将 (dx, bx) 对称的 8 点传入 plot_pixel
76	; 入口：DX=x, BX=y
77	; -------------------------------------------------------
78	plot_octants:
79	; 保存通用寄存
80	push ax
81	push bx
82	push cx
83	push dx
84	push si
85	push di
86
87	; ( x, y)
88	mov si, dx
89	mov di, bx
90	call plot_pixel
91
92	; ( y, x)
93	mov si, bx
94	mov di, dx
95	call plot_pixel
96
97	; (-x, y)
98	mov si, dx
99	neg si
100	mov di, bx
101	call plot_pixel
102
103	; (-y, x)
104	mov si, bx
105	neg si
106	mov di, dx
107	call plot_pixel
108
109	; (-x, -y)
110	mov si, dx
111	neg si
112	mov di, bx
113	neg di
114	call plot_pixel
115
116	; (-y, -x)
117	mov si, bx
118	neg si
119	mov di, dx
120	neg di
121	call plot_pixel
122
123	; ( x, -y)
124	mov si, dx
125	mov di, bx
126	neg di
127	call plot_pixel
128
129	; ( y, -x)
130	mov si, bx
131	mov di, dx
132	neg di
133	call plot_pixel
134
135	; 恢复寄存
136	pop di
137	pop si
138	pop dx
139	pop cx
140	pop bx
141	pop ax
142	ret
143
144	; -------------------------------------------------------
145	; plot_pixel:
146	; SI = x 偏移 (signed), DI = y 偏移 (signed)
147	; 在中心 (160,100) 上绘制一个灰色像素 (palette index = 7)
148	; -------------------------------------------------------
149	plot_pixel:
150	push ax
151	push bx
152	push cx
153	push dx
154
155	; 计算 px = 160 + SI, py = 100 + DI
156	mov ax, 160
157	add ax, si ; px
158	mov cx, 100
159	add cx, di ; py
160
161	; offset = py*320 + px = (py<<8)+(py<<6)+px
162	mov bx, cx
163	shl bx, 8
164	mov di, bx
165	mov bx, cx
166	shl bx, 6
167	add di, bx
168	add di, ax
169
170	mov al, 7 ; gray
171	mov [es:di], al
172
173	pop dx
174	pop cx
175	pop bx
176	pop ax
177	ret
178
179	times 510-($-$$) db 0
180	dw 0xAA55
181
182