Merge pull request #29872 from QuLogic/layout-text-placeholders

TST: Use placeholders for text in layout tests

Author: timhoffm

doc/devel/testing.rst

@@ -163,9 +163,10 @@ the tests, they should now pass.
 
 It is preferred that new tests use ``style='mpl20'`` as this leads to smaller
 figures and reflects the newer look of default Matplotlib plots. Also, if the
-texts (labels, tick labels, etc) are not really part of what is tested, use
-``remove_text=True`` as this will lead to smaller figures and reduce possible
-issues with font mismatch on different platforms.
+texts (labels, tick labels, etc) are not really part of what is tested, use the
+``remove_text=True`` argument or add the ``text_placeholders`` fixture as this
+will lead to smaller figures and reduce possible issues with font mismatch on
+different platforms.
 
 
 Compare two methods of creating an image

lib/matplotlib/testing/conftest.py

@@ -125,3 +125,54 @@ def test_imshow_xarray(xr):
 
     xr = pytest.importorskip('xarray')
     return xr
+
+
+@pytest.fixture
+def text_placeholders(monkeypatch):
+    """
+    Replace texts with placeholder rectangles.
+
+    The rectangle size only depends on the font size and the number of characters. It is
+    thus insensitive to font properties and rendering details. This should be used for
+    tests that depend on text geometries but not the actual text rendering, e.g. layout
+    tests.
+    """
+    from matplotlib.patches import Rectangle
+
+    def patched_get_text_metrics_with_cache(renderer, text, fontprop, ismath, dpi):
+        """
+        Replace ``_get_text_metrics_with_cache`` with fixed results.
+
+        The usual ``renderer.get_text_width_height_descent`` would depend on font
+        metrics; instead the fixed results are based on font size and the length of the
+        string only.
+        """
+        # While get_window_extent returns pixels and font size is in points, font size
+        # includes ascenders and descenders. Leaving out this factor and setting
+        # descent=0 ends up with a box that is relatively close to DejaVu Sans.
+        height = fontprop.get_size()
+        width = len(text) * height / 1.618  # Golden ratio for character size.
+        descent = 0
+        return width, height, descent
+
+    def patched_text_draw(self, renderer):
+        """
+        Replace ``Text.draw`` with a fixed bounding box Rectangle.
+
+        The bounding box corresponds to ``Text.get_window_extent``, which ultimately
+        depends on the above patched ``_get_text_metrics_with_cache``.
+        """
+        if renderer is not None:
+            self._renderer = renderer
+        if not self.get_visible():
+            return
+        if self.get_text() == '':
+            return
+        bbox = self.get_window_extent()
+        rect = Rectangle(bbox.p0, bbox.width, bbox.height,
+                         facecolor=self.get_color(), edgecolor='none')
+        rect.draw(renderer)
+
+    monkeypatch.setattr('matplotlib.text._get_text_metrics_with_cache',
+                        patched_get_text_metrics_with_cache)
+    monkeypatch.setattr('matplotlib.text.Text.draw', patched_text_draw)

lib/matplotlib/testing/conftest.pyi

@@ -10,3 +10,5 @@ def mpl_test_settings(request: pytest.FixtureRequest) -> None: ...
 def pd() -> ModuleType: ...
 @pytest.fixture
 def xr() -> ModuleType: ...
+@pytest.fixture
+def text_placeholders(monkeypatch: pytest.MonkeyPatch) -> None: ...