API: feedback to figure size due to pixel counts

tacaswell · tacaswell · commit 3cdef69b6361 · 2021-12-07T17:48:02.000-05:00
When rasterizing the figure, the allowed sizes are discrete due to a
finite dpi.  When getting the renderer (at which point we have
committed to rasterizing the figure at this dpi) feedback the actual
size.
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -440,7 +440,14 @@ def draw(self):
 
     def get_renderer(self, cleared=False):
         w, h = np.round(self.figure.bbox.size).astype(int)
-        key = w, h, self.figure.dpi
+        dpi = self.figure.dpi
+
+        # we know we are using Agg, thus are tied to discrete sizes
+        # set by the dpi.  Feed this back so that the transforms are
+        # mapped to the available pixels
+        self.figure.set_size_inches(w / dpi, h / dpi)
+
+        key = w, h, dpi
         reuse_renderer = (hasattr(self, "renderer")
                           and getattr(self, "_lastKey", None) == key)
         if not reuse_renderer:
diff --git a/lib/matplotlib/backends/backend_webagg_core.py b/lib/matplotlib/backends/backend_webagg_core.py
@@ -256,10 +256,17 @@ def get_diff_image(self):
                 return png.getvalue()
 
     def get_renderer(self, cleared=None):
-        # Mirrors super.get_renderer, but caches the old one so that we can do
-        # things such as produce a diff image in get_diff_image.
-        w, h = np.round(self.figure.bbox.size).astype(int)
-        key = w, h, self.figure.dpi
+        # Mirrors super.get_renderer, but caches the old one
+        # so that we can do things such as produce a diff image
+        # in get_diff_image
+        w, h = np.round(self.figure.bbox.bounds).astype(int)
+        dpi = self.figure.dpi
+        # we know we are using Agg, thus are tied to discrete sizes
+        # set by the dpi.  Feed this back so that the transforms are
+        # mapped to the available pixels
+        self.figure.set_size_inches(w / dpi, h / dpi)
+
+        key = w, h, dpi
         try:
             self._lastKey, self._renderer
         except AttributeError:
