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"""
Windows/OS2 Bitmap (BMP) this could have been a perfect show-case file format, but they had to make it ugly (all sorts of alignments)
"""
from construct import *
#===============================================================================
# pixels: uncompressed
#===============================================================================
def UncompressedRows(subcon, align_to_byte=False):
"""argh! lines must be aligned to a 4-byte boundary, and bit-pixel lines must be aligned to full bytes..."""
if align_to_byte:
line_pixels = Bitwise(Aligned(8, Array(this.width, subcon)))
else:
line_pixels = Array(this.width, subcon)
return Array(this.height, Aligned(4, line_pixels))
uncompressed_pixels = Switch(this.bpp,
{
1 : UncompressedRows(Bit, align_to_byte=True), # index
4 : UncompressedRows(Nibble, align_to_byte=True), # index
8 : UncompressedRows(Byte), # index
24 : UncompressedRows(Byte[3]), # rgb
}
)
#===============================================================================
# pixels: Run Length Encoding (RLE) 8 bit
#===============================================================================
class RunLengthAdapter(Adapter):
def _decode(self, obj, context, path):
length,value = obj
return [value] * length
def _encode(self, obj, context, path):
return len(obj), obj[0]
# WARNING: not used anywhere
rle8pixel = "rle8pixel" / RunLengthAdapter(Byte >> Byte)
#===============================================================================
# file structure
#===============================================================================
bitmap_file = Struct(
"signature" / Const(b"BM"),
"file_size" / Int32ul,
Padding(4),
"data_offset" / Int32ul,
"header_size" / Int32ul,
"version" / Enum(Computed(this.header_size),
v2 = 12,
v3 = 40,
v4 = 108,
),
"width" / Int32ul,
"height" / Int32ul,
"number_of_pixels" / Computed(this.width * this.height),
"planes" / Int16ul,
"bpp" / Int16ul, # bits per pixel
"compression" / Enum(Int32ul,
Uncompressed = 0,
RLE8 = 1,
RLE4 = 2,
Bitfields = 3,
JPEG = 4,
PNG = 5,
),
"image_data_size" / Int32ul, # in bytes
"horizontal_dpi" / Int32ul,
"vertical_dpi" / Int32ul,
"colors_used" / Int32ul,
"important_colors" / Int32ul,
# palette (24 bit has no palette)
# NOTE: was called "rgb" inside of it
"palette" / Array(lambda ctx: 2**ctx.bpp if ctx.bpp <= 8 else 0,
Padded(4, Byte[3])),
"pixels" / Pointer(this.data_offset,
Switch(this.compression, {"Uncompressed" : uncompressed_pixels}),
),
)
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