1 files changed, 113 insertions, 0 deletions
diff --git a/external/construct/formats/graphics/bmp.py b/external/construct/formats/graphics/bmp.py
new file mode 100644
index 0000000..abe1ad0
--- /dev/null
+++ b/external/construct/formats/graphics/bmp.py
@@ -0,0 +1,113 @@
+"""
+Windows/OS2 Bitmap (BMP)
+this could have been a perfect show-case file format, but they had to make
+it ugly (all sorts of alignment or
+"""
+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(Array(lambda ctx: ctx.width, subcon), modulus = 8)
+        )
+    else:
+        line_pixels = Array(lambda ctx: ctx.width, subcon)
+    return Array(lambda ctx: ctx.height,
+        Aligned(line_pixels, modulus = 4)
+    )
+
+uncompressed_pixels = Switch("uncompressed", lambda ctx: ctx.bpp,
+    {
+        1 : UncompressedRows(Bit("index"), align_to_byte = True),
+        4 : UncompressedRows(Nibble("index"), align_to_byte = True),
+        8 : UncompressedRows(Byte("index")),
+        24 : UncompressedRows(
+            Sequence("rgb", Byte("red"), Byte("green"), Byte("blue"))
+        ),
+    }
+)
+
+#===============================================================================
+# pixels: Run Length Encoding (RLE) 8 bit
+#===============================================================================
+class RunLengthAdapter(Adapter):
+    def _encode(self, obj):
+        return len(obj), obj[0]
+    def _decode(self, obj):
+        length, value = obj
+        return [value] * length
+
+rle8pixel = RunLengthAdapter(
+    Sequence("rle8pixel",
+        Byte("length"),
+        Byte("value")
+    )
+)
+
+#===============================================================================
+# file structure
+#===============================================================================
+bitmap_file = Struct("bitmap_file",
+    # header
+    Const(String("signature", 2), "BM"),
+    ULInt32("file_size"),
+    Padding(4),
+    ULInt32("data_offset"),
+    ULInt32("header_size"),
+    Enum(Alias("version", "header_size"),
+        v2 = 12,
+        v3 = 40,
+        v4 = 108,
+    ),
+    ULInt32("width"),
+    ULInt32("height"),
+    Value("number_of_pixels", lambda ctx: ctx.width * ctx.height),
+    ULInt16("planes"),
+    ULInt16("bpp"), # bits per pixel
+    Enum(ULInt32("compression"),
+        Uncompressed = 0,
+        RLE8 = 1,
+        RLE4 = 2,
+        Bitfields = 3,
+        JPEG = 4,
+        PNG = 5,
+    ),
+    ULInt32("image_data_size"), # in bytes
+    ULInt32("horizontal_dpi"),
+    ULInt32("vertical_dpi"),
+    ULInt32("colors_used"),
+    ULInt32("important_colors"),
+
+    # palette (24 bit has no palette)
+    OnDemand(
+        Array(lambda ctx: 2 ** ctx.bpp if ctx.bpp <= 8 else 0,
+            Struct("palette",
+                Byte("blue"),
+                Byte("green"),
+                Byte("red"),
+                Padding(1),
+            )
+        )
+    ),
+
+    # pixels
+    OnDemandPointer(lambda ctx: ctx.data_offset,
+        Switch("pixels", lambda ctx: ctx.compression,
+            {
+                "Uncompressed" : uncompressed_pixels,
+            }
+        ),
+    ),
+)
+
+
+if __name__ == "__main__":
+    obj = bitmap_file.parse_stream(open("../../../tests/bitmap8.bmp", "rb"))
+    print (obj)
+    print (repr(obj.pixels.value))