Combined BMP RLE decoders

Author: radarhere

src/PIL/BmpImagePlugin.py

@@ -211,10 +211,8 @@ def _bitmap(self, header=0, offset=0):
         elif file_info["compression"] == self.RAW:
             if file_info["bits"] == 32 and header == 22:  # 32-bit .cur offset
                 raw_mode, self.mode = "BGRA", "RGBA"
-        elif file_info["compression"] == self.RLE8:
-            decoder_name = "bmp_rle8"
-        elif file_info["compression"] == self.RLE4:
-            decoder_name = "bmp_rle4"
+        elif file_info["compression"] in (self.RLE8, self.RLE4):
+            decoder_name = "bmp_rle"
         else:
             raise OSError(f"Unsupported BMP compression ({file_info['compression']})")
 
@@ -252,16 +250,18 @@ def _bitmap(self, header=0, offset=0):
 
         # ---------------------------- Finally set the tile data for the plugin
         self.info["compression"] = file_info["compression"]
+        args = [raw_mode]
+        if decoder_name == "bmp_rle":
+            args.append(file_info["compression"] == self.RLE4)
+        else:
+            args.append(((file_info["width"] * file_info["bits"] + 31) >> 3) & (~3))
+        args.append(file_info["direction"])
         self.tile = [
             (
                 decoder_name,
                 (0, 0, file_info["width"], file_info["height"]),
                 offset or self.fp.tell(),
-                (
-                    raw_mode,
-                    ((file_info["width"] * file_info["bits"] + 31) >> 3) & (~3),
-                    file_info["direction"],
-                ),
+                tuple(args),
             )
         ]
 
@@ -278,10 +278,11 @@ def _open(self):
         self._bitmap(offset=offset)
 
 
-class BmpRle8Decoder(ImageFile.PyDecoder):
+class BmpRleDecoder(ImageFile.PyDecoder):
     _pulls_fd = True
 
     def decode(self, buffer):
+        rle4 = self.args[1]
         data = bytearray()
         x = 0
         while len(data) < self.state.xsize * self.state.ysize:
@@ -295,67 +296,19 @@ def decode(self, buffer):
                 if x + num_pixels > self.state.xsize:
                     # Too much data for row
                     num_pixels = max(0, self.state.xsize - x)
-                data += byte * num_pixels
-                x += num_pixels
-            else:
-                if byte[0] == 0:
-                    # end of line
-                    while len(data) % self.state.xsize != 0:
-                        data += b"\x00"
-                    x = 0
-                elif byte[0] == 1:
-                    # end of bitmap
-                    break
-                elif byte[0] == 2:
-                    # delta
-                    bytes_read = self.fd.read(2)
-                    if len(bytes_read) < 2:
-                        break
-                    right, up = self.fd.read(2)
-                    data += b"\x00" * (right + up * self.state.xsize)
-                    x = len(data) % self.state.xsize
+                if rle4:
+                    first_pixel = o8(byte[0] >> 4)
+                    second_pixel = o8(byte[0] & 0x0F)
+                    for index in range(num_pixels):
+                        if index % 2 == 0:
+                            data += first_pixel
+                        else:
+                            data += second_pixel
                 else:
-                    # absolute mode
-                    bytes_read = self.fd.read(byte[0])
-                    data += bytes_read
-                    if len(bytes_read) < byte[0]:
-                        break
-                    x += byte[0]
-
-                    # align to 16-bit word boundary
-                    if self.fd.tell() % 2 != 0:
-                        self.fd.seek(1, os.SEEK_CUR)
-        rawmode = "L" if self.mode == "L" else "P"
-        self.set_as_raw(bytes(data), (rawmode, 0, self.args[-1]))
-        return -1, 0
-
-
-class BmpRle4Decoder(ImageFile.PyDecoder):
-    _pulls_fd = True
-
-    def decode(self, buffer):
-        data = bytearray()
-        x = 0
-        while len(data) < self.state.xsize * self.state.ysize:
-            pixels = self.fd.read(1)
-            byte = self.fd.read(1)
-            if not pixels or not byte:
-                break
-            num_pixels = pixels[0]
-            if num_pixels:
-                # encoded mode
-                if x + num_pixels > self.state.xsize:
-                    # Too much data for row
-                    num_pixels = max(0, self.state.xsize - x)
-                first_pixel = o8(byte[0] >> 4)
-                second_pixel = o8(byte[0] & 0x0F)
-                for index in range(num_pixels):
-                    if index % 2 == 0:
-                        data += first_pixel
-                    else:
-                        data += second_pixel
+                    data += byte * num_pixels
                 x += num_pixels
             else:
+                # absolute mode
                 if byte[0] == 0:
                     # end of line
                     while len(data) % self.state.xsize != 0:
@@ -373,15 +326,18 @@ def decode(self, buffer):
                     data += b"\x00" * (right + up * self.state.xsize)
                     x = len(data) % self.state.xsize
                 else:
-                    # absolute mode (2 pixels per byte)
-                    total_bytes_to_read = byte[0] // 2
-                    bytes_read = self.fd.read(total_bytes_to_read)
-                    for byte_read in bytes_read:
-                        first_pixel = o8(byte_read >> 4)
-                        data += first_pixel
-                        second_pixel = o8(byte_read & 0x0F)
-                        data += second_pixel
-                    if len(bytes_read) < total_bytes_to_read:
+                    if rle4:
+                        # 2 pixels per byte
+                        byte_count = byte[0] // 2
+                        bytes_read = self.fd.read(byte_count)
+                        for byte_read in bytes_read:
+                            data += o8(byte_read >> 4)
+                            data += o8(byte_read & 0x0F)
+                    else:
+                        byte_count = byte[0]
+                        bytes_read = self.fd.read(byte_count)
+                        data += bytes_read
+                    if len(bytes_read) < byte_count:
                         break
                     x += byte[0]
 
@@ -498,8 +454,7 @@ def _save(im, fp, filename, bitmap_header=True):
 
 Image.register_mime(BmpImageFile.format, "image/bmp")
 
-Image.register_decoder("bmp_rle8", BmpRle8Decoder)
-Image.register_decoder("bmp_rle4", BmpRle4Decoder)
+Image.register_decoder("bmp_rle", BmpRleDecoder)
 
 Image.register_open(DibImageFile.format, DibImageFile, _dib_accept)
 Image.register_save(DibImageFile.format, _dib_save)