Merge pull request #2 from radarhere/comment_correct_placement

Once comment is loaded, keep it for subsequent frames

Author: raygard

Tests/images/second_frame_comment.gif

@@ -837,31 +837,48 @@ def test_read_multiple_comment_blocks():
         assert im.info["comment"] == b"Test comment 1\nTest comment 2"
 
 
-def test_write_comment(tmp_path):
+def test_empty_string_comment(tmp_path):
     out = str(tmp_path / "temp.gif")
-    with Image.open("Tests/images/dispose_prev.gif") as im:
-        im.save(out, save_all=True, comment="Test")
-        with Image.open(out) as reread:
-            # Comments written should appear only in first frame
-            assert reread.info["comment"] == b"Test"
-            for i, frame in enumerate(ImageSequence.Iterator(reread)):
-                assert (
-                    i == 0
-                    and frame.info["comment"] == b"Test"
-                    or i != 0
-                    and "comment" not in frame.info
-                )
-
-
-def test_write_no_comment(tmp_path):
+    with Image.open("Tests/images/chi.gif") as im:
+        assert "comment" in im.info
+
+        # Empty string comment should suppress existing comment
+        im.save(out, save_all=True, comment="")
+
+    with Image.open(out) as reread:
+        for frame in ImageSequence.Iterator(reread):
+            assert "comment" not in frame.info
+
+
+def test_retain_comment_in_subsequent_frames(tmp_path):
+    # Test that a comment block at the beginning is kept
+    with Image.open("Tests/images/chi.gif") as im:
+        for frame in ImageSequence.Iterator(im):
+            assert frame.info["comment"] == b"Created with GIMP"
+
+    with Image.open("Tests/images/second_frame_comment.gif") as im:
+        assert "comment" not in im.info
+
+        # Test that a comment in the middle is read
+        im.seek(1)
+        assert im.info["comment"] == b"Comment in the second frame"
+
+        # Test that it is still present in a later frame
+        im.seek(2)
+        assert im.info["comment"] == b"Comment in the second frame"
+
+        # Test that rewinding removes the comment
+        im.seek(0)
+        assert "comment" not in im.info
+
+    # Test that a saved image keeps the comment
     out = str(tmp_path / "temp.gif")
     with Image.open("Tests/images/dispose_prev.gif") as im:
-        # Empty comment="" arg should suppress all comments
-        im.save(out, save_all=True, comment="")
-        with Image.open(out) as reread:
-            assert "comment" not in reread.info
-            for frame in ImageSequence.Iterator(reread):
-                assert "comment" not in frame.info
+        im.save(out, save_all=True, comment="Test")
+
+    with Image.open(out) as reread:
+        for frame in ImageSequence.Iterator(reread):
+            assert frame.info["comment"] == b"Test"
 
 
 def test_version(tmp_path):

Tests/test_file_gif.py

@@ -163,6 +163,8 @@ def _seek(self, frame, update_image=True):
             self.__frame = -1
             self._fp.seek(self.__rewind)
             self.disposal_method = 0
+            if "comment" in self.info:
+                del self.info["comment"]
         else:
             # ensure that the previous frame was loaded
             if self.tile and update_image:
@@ -230,7 +232,7 @@ def _seek(self, frame, update_image=True):
                     #
                     comment = b""
 
-                    # Collect one comment block
+                    # Read this comment block
                     while block:
                         comment += block
                         block = self.data()
@@ -395,7 +397,9 @@ def _rgb(color):
                 )
             ]
 
-        for k in ["duration", "comment", "extension", "loop"]:
+        if info.get("comment"):
+            self.info["comment"] = info["comment"]
+        for k in ["duration", "extension", "loop"]:
             if k in info:
                 self.info[k] = info[k]
             elif k in self.info:
@@ -929,17 +933,18 @@ def _get_global_header(im, info):
         # Global Color Table
         _get_header_palette(palette_bytes),
     ]
+    if info.get("comment"):
+        comment_block = b"!" + o8(254)  # extension intro
 
-    if "comment" in info and len(info["comment"]):
         comment = info["comment"]
         if isinstance(comment, str):
             comment = comment.encode()
-        header.append(b"!" + o8(254))  # extension intro
         for i in range(0, len(comment), 255):
             subblock = comment[i : i + 255]
-            header.append(o8(len(subblock)) + subblock)
-        header.append(o8(0))
+            comment_block += o8(len(subblock)) + subblock
 
+        comment_block += o8(0)
+        header.append(comment_block)
     return header