img: add _PngParser.horz_dpi and .vert_dpi

Steve Canny · Steve Canny · commit c8e0a4f0eb33 · 2014-03-01T01:35:30.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -40,36 +40,6 @@ def from_stream(cls, stream):
 
         return cls(px_width, px_height, horz_dpi, vert_dpi)
 
-    @property
-    def horz_dpi(self):
-        """
-        Integer dots per inch for the width of this image. Defaults to 72
-        when not present in the file, as is often the case.
-        """
-        units_specifier = self._attrs.get(TAG.UNITS_SPECIFIER)
-        horz_px_per_unit = self._attrs.get(TAG.HORZ_PX_PER_UNIT)
-        return self._dpi(units_specifier, horz_px_per_unit)
-
-    @property
-    def vert_dpi(self):
-        """
-        Integer dots per inch for the height of this image. Defaults to 72
-        when not present in the file, as is often the case.
-        """
-        units_specifier = self._attrs.get(TAG.UNITS_SPECIFIER)
-        vert_px_per_unit = self._attrs.get(TAG.VERT_PX_PER_UNIT)
-        return self._dpi(units_specifier, vert_px_per_unit)
-
-    @staticmethod
-    def _dpi(units_specifier, px_per_unit):
-        """
-        Return dots per inch value calculated from *units_specifier* and
-        *px_per_unit*.
-        """
-        if units_specifier == 1 and px_per_unit is not None:
-            return int(round(px_per_unit * 0.0254))
-        return 72
-
     @classmethod
     def _parse_png_headers(cls, stream):
         """
@@ -202,15 +172,31 @@ def horz_dpi(self):
         Integer dots per inch for the width of this image. Defaults to 72
         when not present in the file, as is often the case.
         """
-        raise NotImplementedError
+        pHYs = self._chunks.pHYs
+        if pHYs is None:
+            return 72
+        return self._dpi(pHYs.units_specifier, pHYs.horz_px_per_unit)
 
     @property
     def vert_dpi(self):
         """
         Integer dots per inch for the height of this image. Defaults to 72
         when not present in the file, as is often the case.
         """
-        raise NotImplementedError
+        pHYs = self._chunks.pHYs
+        if pHYs is None:
+            return 72
+        return self._dpi(pHYs.units_specifier, pHYs.vert_px_per_unit)
+
+    @staticmethod
+    def _dpi(units_specifier, px_per_unit):
+        """
+        Return dots per inch value calculated from *units_specifier* and
+        *px_per_unit*.
+        """
+        if units_specifier == 1 and px_per_unit:
+            return int(round(px_per_unit * 0.0254))
+        return 72
 
 
 class _Chunks(object):
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -271,6 +271,16 @@ def it_knows_the_image_width_and_height(self, dimensions_fixture):
         assert png_parser.px_width == px_width
         assert png_parser.px_height == px_height
 
+    def it_knows_the_image_dpi(self, dpi_fixture):
+        png_parser, horz_dpi, vert_dpi = dpi_fixture
+        assert png_parser.horz_dpi == horz_dpi
+        assert png_parser.vert_dpi == vert_dpi
+
+    def it_defaults_image_dpi_to_72(self, no_dpi_fixture):
+        png_parser = no_dpi_fixture
+        assert png_parser.horz_dpi == 72
+        assert png_parser.vert_dpi == 72
+
     # fixtures -------------------------------------------------------
 
     @pytest.fixture
@@ -291,6 +301,34 @@ def dimensions_fixture(self, chunks_):
         png_parser = _PngParser(chunks_)
         return png_parser, px_width, px_height
 
+    @pytest.fixture
+    def dpi_fixture(self, chunks_):
+        horz_px_per_unit, vert_px_per_unit, units_specifier = 1654, 945, 1
+        horz_dpi, vert_dpi = 42, 24
+        chunks_.pHYs.horz_px_per_unit = horz_px_per_unit
+        chunks_.pHYs.vert_px_per_unit = vert_px_per_unit
+        chunks_.pHYs.units_specifier = units_specifier
+        png_parser = _PngParser(chunks_)
+        return png_parser, horz_dpi, vert_dpi
+
+    @pytest.fixture(params=[
+        (-1, -1), (0, 1000), (None, 1000), (1, 0), (1, None)
+    ])
+    def no_dpi_fixture(self, request, chunks_):
+        """
+        Scenarios are: 1) no pHYs chunk in PNG stream, 2) units specifier
+        other than 1; 3) px_per_unit is 0; 4) px_per_unit is None
+        """
+        units_specifier, px_per_unit = request.param
+        if units_specifier == -1:
+            chunks_.pHYs = None
+        else:
+            chunks_.pHYs.horz_px_per_unit = px_per_unit
+            chunks_.pHYs.vert_px_per_unit = px_per_unit
+            chunks_.pHYs.units_specifier = units_specifier
+        png_parser = _PngParser(chunks_)
+        return png_parser
+
     @pytest.fixture
     def parse_fixture(self, stream_, _Chunks_, _PngParser__init_, chunks_):
         return stream_, _Chunks_, _PngParser__init_, chunks_
