Clarify variable names in BdfFontFile

Co-authored-by: Yay295 <Yay295@users.noreply.github.com>

src/PIL/BdfFontFile.py

@@ -64,16 +64,25 @@ def bdf_char(f):
         bitmap.append(s[:-1])
     bitmap = b"".join(bitmap)
 
-    [x, y, l, d] = [int(p) for p in props["BBX"].split()]
+    # The word BBX followed by the width in x (BBw), height in y (BBh),
-    [dx, dy] = [int(p) for p in props["DWIDTH"].split()]
+    # and x and y displacement (BBox, BBoy) of the lower left corner
+    # from the origin of the character.
+    width, height, x_disp, y_disp = [int(p) for p in props["BBX"].split()]
 
-    bbox = (dx, dy), (l, -d - y, x + l, -d), (0, 0, x, y)
+    # The word DWIDTH followed by the width in x and y of the character in device units.
+    dx, dy = [int(p) for p in props["DWIDTH"].split()]
+
+    bbox = (
+        (dx, dy),
+        (x_disp, -y_disp - height, width + x_disp, -y_disp),
+        (0, 0, width, height),
+    )
 
     try:
-        im = Image.frombytes("1", (x, y), bitmap, "hex", "1")
+        im = Image.frombytes("1", (width, height), bitmap, "hex", "1")
     except ValueError:
         # deal with zero-width characters
-        im = Image.new("1", (x, y))
+        im = Image.new("1", (width, height))
 
     return id, int(props["ENCODING"]), bbox, im