Convert files to PNG before computing hash

Author: astrofrog

pytest_mpl/plugin.py

@@ -453,12 +453,21 @@ def generate_image_hash(self, item, fig):
         compare = get_compare(item)
         savefig_kwargs = compare.kwargs.get('savefig_kwargs', {})
 
-        imgdata = io.BytesIO()
-
-        fig.savefig(imgdata, **savefig_kwargs)
+        ext = self._file_extension(item)
 
-        out = _hash_file(imgdata)
-        imgdata.close()
+        if ext == 'png':
+            imgdata = io.BytesIO()
+            fig.savefig(imgdata, **savefig_kwargs)
+            out = _hash_file(imgdata)
+            imgdata.close()
+        else:
+            # Always convert to PNG to compute hash as some vector graphics
+            # outputs cannot be made deterministic
+            from matplotlib.testing.compare import convert as convert_to_png
+            img_filename = tempfile.mktemp() + f'.{ext}'
+            fig.savefig(img_filename, **savefig_kwargs)
+            png_filename = convert_to_png(img_filename, cache=True)
+            out = _hash_file(open(png_filename, 'rb'))
 
         close_mpl_figure(fig)
         return out

tests/test_pytest_mpl.py

@@ -691,9 +691,6 @@ def test_formats(pytester, use_hash_library, passes, file_format):
         else:
             pytest.skip('Comparing EPS and PDF files requires ghostscript to be installed')
 
-    if use_hash_library:
-        pytest.skip('Using the hash library does not currently work because the hashes are not deterministic')
-
     pytester.makepyfile(
         f"""
         import pytest