FIX: Check for fontsize smaller than 1 pt

jklymak · jklymak · commit 8a6e4f82beb3 · 2017-12-14T14:17:53.000-08:00
diff --git a/doc/api/api_changes/2017-12-14-JMK.rst b/doc/api/api_changes/2017-12-14-JMK.rst
@@ -0,0 +1,10 @@
+Fontsizes less than 1 pt are clipped to be 1 pt.
+------------------------------------------------
+
+FreeType doesn't allow fonts to get smaller than 1 pt, so all Agg
+backends were silently rounding up to 1 pt.  PDF (other vector
+backends?) were letting us write fonts that were less than 1 pt, but
+they could not be placed properly because position information comes from
+FreeType.  This change makes it so no backends can use fonts smaller than
+1 pt, consistent with FreeType and ensuring more consistent results across
+backends.
diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
@@ -878,6 +878,10 @@ def set_size(self, size):
                     + ", ".join(map(str, font_scalings)))
             else:
                 size = scale * FontManager.get_default_size()
+        if size < 1.0:
+            _log.info('Fontsize %1.2f < 1.0 pt not allowed by FreeType. '
+                      'Setting fontsize = 1 pt' % size)
+            size = 1.0
         self._size = size
 
     def set_file(self, file):
