Microsoft screensaver sample A8 to TGA decoder

a8_to_tga.py

# decodes the A8 files in
# Microsoft Windows NT 4.0 SDK (1996)
# MSTOOLS\SAMPLES\OPENGL\SCRSAVE\MAZE
#
# based on MSTOOLS\SAMPLES\OPENGL\SCRSAVE\COMMON\SSA8.C
 
import struct
 
def a8decompress(d):
    # defines
    ESCAPE = 0
    ESC_ENDLINE = 0
    ESC_ENDBITMAP = 1
    ESC_DELTA = 2
    ESC_RANDOM = 3
    def RANDOM_COUNT(c):
        return c - (ESC_RANDOM-1)
    # HwuRld
    s = 0
    o = []
    while True:
        run = d[s+0]
        esc = d[s+1]
        s += 2
        if run == ESCAPE:
            if esc == ESC_ENDBITMAP:
                break
            elif esc == ESC_DELTA:
                ln = struct.unpack("<H",d[s:s+2])[0]
                s += 2
                while ln > 0:
                    o.append(0)
                    ln -= 1
            elif esc >= ESC_RANDOM:
                ln = RANDOM_COUNT(esc)
                while ln > 0:
                    o.append(d[s])
                    s += 1
                    ln -= 1
        else:
            while run > 0:
                o.append(esc)
                run -= 1
    return o
 
def a8_to_tga(filea8,filetga=None):
    if filetga == None:
        filetga = filea8 + ".TGA"
        filea8 = filea8 + ".A8"
    a8 = open(filea8,"rb").read()
    (a8tag,w,h,a8bpp,a8compress,a8compsize) = struct.unpack("<LLLLLL",a8[0:24])
    a8pal = a8[24:24+(256*4) ]
    a8pix = a8[   24+(256*4):]
    tga = bytearray()
    tga.append(0) # idlength
    tga.append(0) # colourmap = none
    tga.append(2) # datatypecode = RGB
    tga += bytes([0,0,0,0,0]) # colourmap specification ignored
    tga += bytes(struct.pack("<H",0)) # x origin
    tga += bytes(struct.pack("<H",0)) # y origin
    tga += bytes(struct.pack("<H",w)) # width
    tga += bytes(struct.pack("<H",h)) # height
    tga.append(32) # bits per pixel
    tga.append(0x08) # image descriptor: 8 bit alpha, lower left origin
    pal = []
    for i in range(256):
        pal.append(a8pal[i*4:i*4+4])
    if (a8compress != 0):
        a8pix = a8decompress(a8pix)
    for i in range(w*h):
        a8idx = a8pix[i]
        bgra = pal[a8idx]
        tga.append(bgra[0]) # B
        tga.append(bgra[1]) # G
        tga.append(bgra[2]) # R
        tga.append(bgra[3]) # A
    open(filetga,"wb").write(tga)
    print (filea8 + " > " + filetga + " (%d x %d)" % (w,h))
 
a8_to_tga("BHOLE")
a8_to_tga("CURL4")
a8_to_tga("HAPPY")
a8_to_tga("LETTERS")
a8_to_tga("RAT")
a8_to_tga("SNOWFLAK")
a8_to_tga("START")
a8_to_tga("SWIRLX4")