boot_driveno equ 7b00h ; 1 byte
stage2_size equ stage2_end - stage2_start
+spawn_rate equ 5
+framebuf equ 40000h
+
start:
xor ax, ax
mov ds, ax
xor ax, ax
mov es, ax
+ mov ds, ax
mov ax, str_booting
call printstr
.hang: hlt
jmp .hang
+ ; splash screen effect
splash:
mov ax, 13h
int 10h
+ ; setup ramdac colormap
+ mov ax, pal
+ shr ax, 4
+ mov ds, ax
+ xor ax, ax
+ mov dx, 3c8h
+ out dx, al
+ inc dx
+ xor bx, bx
+.cmap_loop:
+ mov al, [bx]
+ shr al, 2
+ out dx, al
+ inc bx
+ cmp bx, 768 ; 256 * 3
+ jnz .cmap_loop
+
+ ; decompress image
+ mov ax, img
+ shr ax, 4
+ mov es, ax
+ xor di, di
+ mov ax, imgrle
+ shr ax, 4
+ mov ds, ax
+ xor si, si
+ mov cx, 64000
+ call decode_rle
+
+ ; precalculate spawn points
+ mov ax, es
+ mov ds, ax ; decompressed image -> ds:bx
+ xor bx, bx
+ mov ax, spawn_pos
+ shr ax, 4
+ mov es, ax ; spawn_pos table segment -> es:dx
+ xor edx, edx
+
+ mov cx, 64000
+.calcspawn_loop:
+ mov al, [bx]
+ test al, 0x80
+ jz .notspawn
+ mov [es:edx * 2], bx
+ inc edx
+.notspawn:
+ inc bx
+ dec cx
+ jnz .calcspawn_loop
+ ; update num_spawn_pos
+ xor ax, ax
+ mov ds, ax
+ mov [num_spawn_pos], edx
+
+ mov ax, framebuf >> 4
+ mov fs, ax ; fs will point to the off-screen framebuffer
+
+ ; effect main loop
+.mainloop:
+ mov cx, spawn_rate
+.spawn: call rand
+ xor edx, edx
+ div dword [num_spawn_pos] ; edx <- rand % num_spawn_pos
+ mov bx, [es:edx * 2] ; grab one of the spawn positions
+ mov byte [fs:bx], 0xff ; plot a pixel there
+ dec cx
+ jnz .spawn
+
+ ; blur the screen upwards
+ mov ax, fs
+ mov ds, ax ; let's use ds for this to avoid long instructions
+ xor bx, bx ; use: pointer
+ xor ax, ax ; use: pixel accum
+ xor dx, dx ; use: second pixel
+.blurloop:
+ mov al, [bx]
+ mov dl, [bx + 320]
+ add ax, dx
+ shr ax, 1
+ mov [bx], al
+ inc bx
+ cmp bx, 64000 - 320
+ jnz .blurloop
+
+
+ ; wait until the start of vblank
+.waitvblank:
+ mov dx, 3dah
+ in al, dx
+ and al, 8
+ jz .waitvblank
+
+ ; copy to screen
+ push es
mov ax, 0a000h
mov es, ax
xor di, di
- mov cx, 32000
- mov ax, 0505h
- rep stosw
+ mov ax, fs
+ mov ds, ax
+ xor si, si
+ mov ecx, 16000
+ rep movsd
+ pop es
+ xor ax, ax
+ mov ds, ax
- call waitkey
+ ; check for keypress
+ in al, 64h
+ and al, 1
+ jz .mainloop
+ in al, 60h
- mov ax, 3
+.end: mov ax, 3
int 10h
+ ret
+
+ ; decode RLE from ds:si to es:di, cx: number of decoded bytes (0 means 65536)
+ ; - high bit set for the repetition count, followed by a value byte to
+ ; be repeated N times
+ ; - high bit not set for raw data that should be copied directly
+decode_rle:
+ mov al, [si]
+ inc si
+ mov bl, 1 ; default to "copy once" for raw values
+ test al, 0x80 ; test the high bit to see if it's a count or a raw value
+ jz .copy
+ ; it's a count, clear the high bit, and read the next byte for the value
+ and al, 0x7f
+ mov bl, al
+ mov al, [si]
+ inc si
+.copy: mov [es:di], al
+ inc di
+ dec cx ; decrement decoded bytes counter
+ jz .end ; as soon as it reaches 0, bail
+ dec bl
+ jnz .copy
+ jmp decode_rle
+.end: ret
+
waitkey:
in al, 64h
in al, 60h
ret
+rand:
+ mov eax, [randval]
+ mul dword [randmul]
+ add eax, 12345
+ and eax, 0x7fffffff
+ mov [randval], eax
+ shr eax, 16
+ ret
+
+randmul dd 1103515245
+randval dd 0ace1h
+
+
+ ; data
+num_spawn_pos dd 0
+ align 16
+spawn_pos:
+imgrle: incbin "nuclear.rle"
+ align 16
+img:
+pal: incbin "fire.pal"
+
stage2_end:
; vi:set ft=nasm:
projects / bootsplash / blobdiff