FIX/API: fig.canvas.draw always updates internal state

tacaswell · tacaswell · commit b7ccfb66066e · 2021-02-15T20:25:47.000-05:00
Previously the non-interactive backends, other than Agg, did not define `draw` methods and fell back to the base no-op version. However, we have been documenting that the correct way to update the various internal state we keep (run tight/constrained layouts, auto limits, text size/position, ...), this is now a bug due to our suggested usage drifting. closes #18407
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -1584,6 +1584,12 @@ def _draw(renderer): raise Done(renderer)
             figure.canvas = orig_canvas
 
 
+def _no_output_draw(figure):
+    renderer = _get_renderer(figure)
+    with renderer._draw_disabled():
+        figure.draw(renderer)
+
+
 def _is_non_interactive_terminal_ipython(ip):
     """
     Return whether we are in a a terminal IPython, but non interactive.
@@ -1621,7 +1627,9 @@ def _check_savefig_extra_args(func=None, extra_kwargs=()):
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
         name = 'savefig'  # Reasonable default guess.
-        public_api = re.compile(r'^savefig|print_[A-Za-z0-9]+$')
+        public_api = re.compile(
+            r'^savefig|print_[A-Za-z0-9]+|_no_output_draw$'
+        )
         seen_print_figure = False
         for frame, line in traceback.walk_stack(None):
             if frame is None:
@@ -1632,8 +1640,9 @@ def wrapper(*args, **kwargs):
                         frame.f_globals.get('__name__', '')):
                 if public_api.match(frame.f_code.co_name):
                     name = frame.f_code.co_name
-                    if name == 'print_figure':
+                    if name in ('print_figure', '_no_output_draw'):
                         seen_print_figure = True
+
             else:
                 break
 
diff --git a/lib/matplotlib/backends/backend_pdf.py b/lib/matplotlib/backends/backend_pdf.py
@@ -28,7 +28,7 @@
 from matplotlib._pylab_helpers import Gcf
 from matplotlib.backend_bases import (
     _Backend, _check_savefig_extra_args, FigureCanvasBase, FigureManagerBase,
-    GraphicsContextBase, RendererBase)
+    GraphicsContextBase, RendererBase, _no_output_draw)
 from matplotlib.backends.backend_mixed import MixedModeRenderer
 from matplotlib.figure import Figure
 from matplotlib.font_manager import findfont, get_font
@@ -2730,6 +2730,9 @@ def print_pdf(self, filename, *,
             else:            # we opened the file above; now finish it off
                 file.close()
 
+    def draw(self):
+        _no_output_draw(self.figure)
+        return super().draw()
 
 FigureManagerPdf = FigureManagerBase
 
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -19,7 +19,8 @@
 from matplotlib import _api, cbook, font_manager as fm
 from matplotlib.backend_bases import (
     _Backend, _check_savefig_extra_args, FigureCanvasBase, FigureManagerBase,
-    GraphicsContextBase, RendererBase)
+    GraphicsContextBase, RendererBase, _no_output_draw
+)
 from matplotlib.backends.backend_mixed import MixedModeRenderer
 from matplotlib.backends.backend_pdf import (
     _create_pdf_info_dict, _datetime_to_pdf)
@@ -906,6 +907,10 @@ def print_png(self, fname_or_fh, *args, **kwargs):
     def get_renderer(self):
         return RendererPgf(self.figure, None)
 
+    def draw(self):
+        _no_output_draw(self.figure)
+        return super().draw()
+
 
 FigureManagerPgf = FigureManagerBase
 
diff --git a/lib/matplotlib/backends/backend_ps.py b/lib/matplotlib/backends/backend_ps.py
@@ -23,7 +23,7 @@
 from matplotlib.afm import AFM
 from matplotlib.backend_bases import (
     _Backend, _check_savefig_extra_args, FigureCanvasBase, FigureManagerBase,
-    GraphicsContextBase, RendererBase)
+    GraphicsContextBase, RendererBase, _no_output_draw)
 from matplotlib.cbook import is_writable_file_like, file_requires_unicode
 from matplotlib.font_manager import get_font
 from matplotlib.ft2font import LOAD_NO_HINTING, LOAD_NO_SCALE
@@ -1129,6 +1129,9 @@ def _print_figure_tex(
 
             _move_path_to_path_or_stream(tmpfile, outfile)
 
+    def draw(self):
+        _no_output_draw(self.figure)
+        return super().draw()
 
 def convert_psfrags(tmpfile, psfrags, font_preamble, custom_preamble,
                     paper_width, paper_height, orientation):
diff --git a/lib/matplotlib/backends/backend_svg.py b/lib/matplotlib/backends/backend_svg.py
@@ -17,7 +17,7 @@
 from matplotlib import _api, cbook
 from matplotlib.backend_bases import (
      _Backend, _check_savefig_extra_args, FigureCanvasBase, FigureManagerBase,
-     RendererBase)
+     RendererBase, _no_output_draw)
 from matplotlib.backends.backend_mixed import MixedModeRenderer
 from matplotlib.colors import rgb2hex
 from matplotlib.dates import UTC
@@ -1363,6 +1363,9 @@ def _print_svg(self, filename, fh, *, dpi=None, bbox_inches_restore=None,
     def get_default_filetype(self):
         return 'svg'
 
+    def draw(self):
+        _no_output_draw(self.figure)
+        return super().draw()
 
 FigureManagerSVG = FigureManagerBase
 
diff --git a/lib/matplotlib/tests/test_backend_bases.py b/lib/matplotlib/tests/test_backend_bases.py
@@ -187,3 +187,36 @@ def test_toolbar_zoompan():
     assert ax.get_navigate_mode() == "ZOOM"
     ax.figure.canvas.manager.toolmanager.trigger_tool('pan')
     assert ax.get_navigate_mode() == "PAN"
+
+
+@pytest.mark.parametrize("backend", ['svg', 'pgf', 'ps', 'pdf'])
+def test_draw(backend):
+    from matplotlib.figure import Figure
+    from matplotlib.backends.backend_agg import FigureCanvas
+    test_backend = pytest.importorskip(
+        f'matplotlib.backends.backend_{backend}'
+    )
+    TestCanvas = test_backend.FigureCanvas
+    fig_test = Figure(constrained_layout=True)
+    TestCanvas(fig_test)
+    axes_test = fig_test.subplots(2, 2)
+
+    # defaults to FigureCanvasBase
+    fig_agg = Figure(constrained_layout=True)
+    # put a backends.backend_agg.FigureCanvas on it
+    FigureCanvas(fig_agg)
+    axes_agg = fig_agg.subplots(2, 2)
+
+    init_pos = [ax.get_position() for ax in axes_test.ravel()]
+
+    fig_test.canvas.draw()
+    fig_agg.canvas.draw()
+
+    layed_out_pos_test = [ax.get_position() for ax in axes_test.ravel()]
+    layed_out_pos_agg = [ax.get_position() for ax in axes_agg.ravel()]
+
+    for init, placed in zip(init_pos, layed_out_pos_test):
+        assert not np.allclose(init, placed, atol=0.005)
+
+    for ref, test in zip(layed_out_pos_agg, layed_out_pos_test):
+        np.testing.assert_allclose(ref, test, atol=0.005)
