API: feedback to figure size due to pixel counts

tacaswell · tacaswell · commit 701ae74b8060 · 2022-12-04T20:37:01.000-05:00
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
@@ -405,6 +405,13 @@ def draw(self):
     @_api.delete_parameter("3.6", "cleared", alternative="renderer.clear()")
     def get_renderer(self, cleared=False):
         w, h = np.round(self.figure.bbox.size).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, self.figure.dpi
         reuse_renderer = (self._lastKey == key)
         if not reuse_renderer:
