Add support for GIF files

adafruit_imageload/__init__.py

@@ -50,4 +50,7 @@ def load(filename, *, bitmap=None, palette=None):
         if header.startswith(b"P"):
             from . import pnm
             return pnm.load(file, header, bitmap=bitmap, palette=palette)
+        if header.startswith(b"GIF"):
+            from . import gif
+            return gif.load(file, bitmap=bitmap, palette=palette)
         raise RuntimeError("Unsupported image format")

adafruit_imageload/gif.py

@@ -0,0 +1,167 @@
+# The MIT License (MIT)
+#
+# Copyright (c) 2019 Radomir Dopieralski
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+"""
+`adafruit_imageload.gif`
+====================================================
+
+Load pixel values (indices or colors) into a bitmap and colors into a palette
+from a GIF file.
+
+* Author(s): Radomir Dopieralski
+
+"""
+
+import struct
+
+
+__version__ = "0.0.0-auto.0"
+__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_ImageLoad.git"
+
+
+def load(file, *, bitmap=None, palette=None):
+    """Loads a GIF image from the open ``file``.
+
+       Returns tuple of bitmap object and palette object.
+
+       :param object bitmap: Type to store bitmap data. Must have API similar to `displayio.Bitmap`.
+         Will be skipped if None
+       :param object palette: Type to store the palette. Must have API similar to
+         `displayio.Palette`. Will be skipped if None"""
+    header = file.read(6)
+    if header not in {b'GIF87a', b'GIF89a'}:
+        raise ValueError("Not a GIF file")
+    width, height, flags, _, _ = struct.unpack('<HHBBB', file.read(7))
+    if (flags & 0x80) != 0:
+        palette_size = 1 << ((flags & 0x07) + 1)
+        palette_obj = palette(palette_size)
+        for i in range(palette_size):
+            palette_obj[i] = file.read(3)
+    else:
+        palette_obj = None
+    color_bits = ((flags & 0x70) >> 4) + 1
+    bitmap_obj = bitmap(width, height, (1 << color_bits) - 1)
+    while True:
+        block_type = file.read(1)[0]
+        if block_type == 0x2c: # frame
+            _read_frame(file, bitmap_obj)
+        elif block_type == 0x21: # extension
+            _ = file.read(1)[0]
+            # 0x01 = label, 0xfe = comment
+            _ = bytes(_read_blockstream(file))
+        elif block_type == 0x3b: # terminator
+            break
+        else:
+            raise ValueError("Bad block type")
+    return bitmap_obj, palette_obj
+
+
+def _read_frame(file, bitmap):
+    """Read a signle frame and apply it to the bitmap."""
+    ddx, ddy, width, _, flags = struct.unpack('<HHHHB', file.read(9))
+    if (flags & 0x40) != 0:
+        raise NotImplementedError("Interlacing not supported")
+    if (flags & 0x80) != 0:
+        palette_size = 1 << ((flags & 0x07) + 1)
+        for _ in range(palette_size):
+            _ = file.read(3)
+    min_code_size = file.read(1)[0]
+    x = 0
+    y = 0
+    for decoded in lzw_decode(_read_blockstream(file), min_code_size):
+        for byte in decoded:
+            bitmap[ddx + x, ddy + y] = byte
+            x += 1
+            if x >= width:
+                x = 0
+                y += 1
+
+
+def _read_blockstream(file):
+    """Read a block from a file."""
+    while True:
+        size = file.read(1)[0]
+        if size == 0:
+            break
+        for _ in range(size):
+            yield file.read(1)[0]
+
+
+class EndOfData(Exception):
+    """Signified end of compressed data."""
+
+
+class LZWDict:
+    """A dictionary of LZW codes."""
+    def __init__(self, code_size):
+        self.code_size = code_size
+        self.clear_code = 1 << code_size
+        self.end_code = self.clear_code + 1
+        self.codes = []
+        self.last = None
+        self.clear()
+
+    def clear(self):
+        """Reset the dictionary to default codes."""
+        self.last = b''
+        self.code_len = self.code_size + 1
+        self.codes[:] = []
+
+    def decode(self, code):
+        """Decode a code."""
+        if code == self.clear_code:
+            self.clear()
+            return b''
+        elif code == self.end_code:
+            raise EndOfData()
+        elif code < self.clear_code:
+            value = bytes([code])
+        elif code <= len(self.codes) + self.end_code:
+            value = self.codes[code - self.end_code - 1]
+        else:
+            value = self.last + self.last[0:1]
+        if self.last:
+            self.codes.append(self.last + value[0:1])
+        if (len(self.codes) + self.end_code + 1 >= 1 << self.code_len and
+                self.code_len < 12):
+            self.code_len += 1
+        self.last = value
+        return value
+
+
+def lzw_decode(data, code_size):
+    """Decode LZW-compressed data."""
+    dictionary = LZWDict(code_size)
+    bit = 0
+    byte = next(data) # pylint: disable=stop-iteration-return
+    try:
+        while True:
+            code = 0
+            for i in range(dictionary.code_len):
+                code |= ((byte >> bit) & 0x01) << i
+                bit += 1
+                if bit >= 8:
+                    bit = 0
+                    byte = next(data) # pylint: disable=stop-iteration-return
+            yield dictionary.decode(code)
+    except EndOfData:
+        while True:
+            next(data) # pylint: disable=stop-iteration-return