img: add _pHYsChunk

Steve Canny · Steve Canny · commit 8ab2f34fcd20 · 2014-03-01T01:35:30.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -327,10 +327,34 @@ class _pHYsChunk(_Chunk):
     """
     pYHs chunk, contains the image dpi information
     """
+    def __init__(self, chunk_type, horz_px_per_unit, vert_px_per_unit,
+                 units_specifier):
+        super(_pHYsChunk, self).__init__(chunk_type)
+        self._horz_px_per_unit = horz_px_per_unit
+        self._vert_px_per_unit = vert_px_per_unit
+        self._units_specifier = units_specifier
+
     @classmethod
     def from_offset(cls, chunk_type, stream_rdr, offset):
         """
         Return a _pHYsChunk instance containing the image resolution
         extracted from the pHYs chunk in *stream* at *offset*.
         """
-        raise NotImplementedError
+        horz_px_per_unit = stream_rdr.read_long(offset)
+        vert_px_per_unit = stream_rdr.read_long(offset, 4)
+        units_specifier = stream_rdr.read_byte(offset, 8)
+        return cls(
+            chunk_type, horz_px_per_unit, vert_px_per_unit, units_specifier
+        )
+
+    @property
+    def horz_px_per_unit(self):
+        return self._horz_px_per_unit
+
+    @property
+    def vert_px_per_unit(self):
+        return self._vert_px_per_unit
+
+    @property
+    def units_specifier(self):
+        return self._units_specifier
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -523,3 +523,30 @@ def from_offset_fixture(self):
         stream_rdr = StreamReader(BytesIO(bytes_), BIG_ENDIAN)
         offset, px_width, px_height = 0, 42, 24
         return stream_rdr, offset, px_width, px_height
+
+
+class Describe_pHYsChunk(object):
+
+    def it_can_construct_from_a_stream_and_offset(self, from_offset_fixture):
+        stream_rdr, offset = from_offset_fixture[:2]
+        horz_px_per_unit, vert_px_per_unit = from_offset_fixture[2:4]
+        units_specifier = from_offset_fixture[4]
+        pHYs_chunk = _pHYsChunk.from_offset(None, stream_rdr, offset)
+        assert isinstance(pHYs_chunk, _pHYsChunk)
+        assert pHYs_chunk.horz_px_per_unit == horz_px_per_unit
+        assert pHYs_chunk.vert_px_per_unit == vert_px_per_unit
+        assert pHYs_chunk.units_specifier == units_specifier
+
+    # fixtures -------------------------------------------------------
+
+    @pytest.fixture
+    def from_offset_fixture(self):
+        bytes_ = b'\x00\x00\x00\x2A\x00\x00\x00\x18\x01'
+        stream_rdr = StreamReader(BytesIO(bytes_), BIG_ENDIAN)
+        offset, horz_px_per_unit, vert_px_per_unit, units_specifier = (
+            0, 42, 24, 1
+        )
+        return (
+            stream_rdr, offset, horz_px_per_unit, vert_px_per_unit,
+            units_specifier
+        )
