random point spawn

diff --git a/bootsplash.asm b/bootsplash.asm
index a6a552a..03e3a50 100644 (file)
--- a/bootsplash.asm
+++ b/bootsplash.asm
@@ -5,6 +5,9 @@ stacktop equ 7b00h
 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
@@ -75,21 +78,102 @@ splash:
        mov ax, 13h
        int 10h
 
-       mov ax, 0a000h
+       ; 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, pic
+       mov ax, imgrle
        shr ax, 4
        mov ds, ax
        xor si, si
-
        mov cx, 64000
        call decode_rle
 
-       call waitkey
+       ; 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 10 points per frame
+.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], 1             ; plot a pixel there
+       dec cx
+       jnz .spawn
+
+       ; 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 ax, fs
+       mov ds, ax
+       xor si, si
+       mov ecx, 16000
+       rep movsd
+       pop es
+       xor ax, ax
+       mov ds, ax
+
+       ; check for keypress
+       in al, 64h
+       and al, 1
+       jz .mainloop
+       in al, 60h
 
-       mov ax, 3
+.end:  mov ax, 3
        int 10h
        ret
 
@@ -125,9 +209,27 @@ waitkey:
        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
-pic:   incbin "nuclear.rle"
+img:
+pal:   incbin "fire.pal"
 
 stage2_end: