RLE blitter, plus RLE encoding and decoding tools

[bootsplash] / bootsplash.asm

diff --git a/bootsplash.asm b/bootsplash.asm
index e8c4cc7..a6a552a 100644 (file)
--- a/bootsplash.asm
+++ b/bootsplash.asm
@@ -61,6 +61,7 @@ stage2_start:
 
        xor ax, ax
        mov es, ax
+       mov ds, ax
 
        mov ax, str_booting
        call printstr
@@ -69,6 +70,7 @@ stage2_start:
 .hang: hlt
        jmp .hang
 
+       ; splash screen effect
 splash:
        mov ax, 13h
        int 10h
@@ -76,14 +78,45 @@ splash:
        mov ax, 0a000h
        mov es, ax
        xor di, di
-       mov cx, 32000
-       mov ax, 0505h
-       rep stosw
+
+       mov ax, pic
+       shr ax, 4
+       mov ds, ax
+       xor si, si
+
+       mov cx, 64000
+       call decode_rle
 
        call waitkey
 
        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
@@ -92,6 +125,10 @@ waitkey:
        in al, 60h
        ret
 
+       ; data
+       align 16
+pic:   incbin "nuclear.rle"
+
 stage2_end:
 
 ; vi:set ft=nasm: