matplotlib · anntzer · Sep 14, 2021 · Sep 9, 2021 · Sep 9, 2021 · Sep 9, 2021
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2259,6 +2259,7 @@ def print_figure(
         # Remove the figure manager, if any, to avoid resizing the GUI widget.
         with cbook._setattr_cm(self, manager=None), \
              cbook._setattr_cm(self.figure, dpi=dpi), \
+             cbook._setattr_cm(canvas, _device_pixel_ratio=1), \
              cbook._setattr_cm(canvas, _is_saving=True), \
              ExitStack() as stack:
 

diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -245,7 +245,7 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
 
             ctx.save()
             ctx.select_font_face(*_cairo_font_args_from_font_prop(prop))
-            ctx.set_font_size(prop.get_size_in_points() * self.dpi / 72)
+            ctx.set_font_size(self.points_to_pixels(prop.get_size_in_points()))
             opts = cairo.FontOptions()
             opts.set_antialias(
                 cairo.ANTIALIAS_DEFAULT if mpl.rcParams["text.antialiased"]
@@ -271,7 +271,7 @@ def _draw_mathtext(self, gc, x, y, s, prop, angle):
             ctx.move_to(ox, -oy)
             ctx.select_font_face(
                 *_cairo_font_args_from_font_prop(ttfFontProperty(font)))
-            ctx.set_font_size(fontsize * self.dpi / 72)
+            ctx.set_font_size(self.points_to_pixels(fontsize))
             ctx.show_text(chr(idx))
 
         for ox, oy, w, h in rects:
@@ -303,9 +303,7 @@ def get_text_width_height_descent(self, s, prop, ismath):
         # save/restore prevents the problem
         ctx.save()
         ctx.select_font_face(*_cairo_font_args_from_font_prop(prop))
-        # Cairo (says it) uses 1/96 inch user space units, ref: cairo_gstate.c
-        # but if /96.0 is used the font is too small
-        ctx.set_font_size(prop.get_size_in_points() * self.dpi / 72)
+        ctx.set_font_size(self.points_to_pixels(prop.get_size_in_points()))
 
         y_bearing, w, h = ctx.text_extents(s)[1:4]
         ctx.restore()

diff --git a/lib/matplotlib/backends/backend_gtk3cairo.py b/lib/matplotlib/backends/backend_gtk3cairo.py
@@ -28,6 +28,7 @@ def on_draw_event(self, widget, ctx):
                 allocation.width, allocation.height)
             self._renderer.set_width_height(
                 allocation.width, allocation.height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
 
 

diff --git a/lib/matplotlib/backends/backend_gtk4cairo.py b/lib/matplotlib/backends/backend_gtk4cairo.py
@@ -27,6 +27,7 @@ def on_draw_event(self, widget, ctx):
                 allocation.width, allocation.height)
             self._renderer.set_width_height(
                 allocation.width, allocation.height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
 
 

diff --git a/lib/matplotlib/backends/backend_qtcairo.py b/lib/matplotlib/backends/backend_qtcairo.py
@@ -13,6 +13,7 @@ def __init__(self, figure=None):
 
     def draw(self):
         if hasattr(self._renderer.gc, "ctx"):
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
         super().draw()
 
@@ -23,6 +24,7 @@ def paintEvent(self, event):
             surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
             self._renderer.set_ctx_from_surface(surface)
             self._renderer.set_width_height(width, height)
+            self._renderer.dpi = self.figure.dpi
             self.figure.draw(self._renderer)
         buf = self._renderer.gc.ctx.get_target().get_data()
         if QT_API == "PyQt6":

diff --git a/lib/matplotlib/backends/backend_tkcairo.py b/lib/matplotlib/backends/backend_tkcairo.py
@@ -18,6 +18,7 @@ def draw(self):
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
         self._renderer.set_ctx_from_surface(surface)
         self._renderer.set_width_height(width, height)
+        self._renderer.dpi = self.figure.dpi
         self.figure.draw(self._renderer)
         buf = np.reshape(surface.get_data(), (height, width, 4))
         _backend_tk.blit(

diff --git a/lib/matplotlib/backends/backend_wxcairo.py b/lib/matplotlib/backends/backend_wxcairo.py
@@ -35,6 +35,7 @@ def draw(self, drawDC=None):
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
         self._renderer.set_ctx_from_surface(surface)
         self._renderer.set_width_height(width, height)
+        self._renderer.dpi = self.figure.dpi
         self.figure.draw(self._renderer)
         self.bitmap = wxcairo.BitmapFromImageSurface(surface)
         self._isDrawn = True

diff --git a/lib/matplotlib/tests/test_figure.py b/lib/matplotlib/tests/test_figure.py
@@ -6,6 +6,10 @@
 from types import SimpleNamespace
 import warnings
 
+import numpy as np
+import pytest
+from PIL import Image
+
 import matplotlib as mpl
 from matplotlib import cbook, rcParams
 from matplotlib._api.deprecation import MatplotlibDeprecationWarning
@@ -16,8 +20,6 @@
 import matplotlib.pyplot as plt
 import matplotlib.dates as mdates
 import matplotlib.gridspec as gridspec
-import numpy as np
-import pytest
 
 
 @image_comparison(['figure_align_labels'], extensions=['png', 'svg'],
@@ -496,6 +498,29 @@ def test_savefig_backend():
         fig.savefig("test.png", backend="pdf")
 
 
+@pytest.mark.parametrize('backend', [
+    pytest.param('Agg', marks=[pytest.mark.backend('Agg')]),
+    pytest.param('Cairo', marks=[pytest.mark.backend('Cairo')]),
+])
+def test_savefig_pixel_ratio(backend):
+    fig, ax = plt.subplots()
+    ax.plot([1, 2, 3])
+    with io.BytesIO() as buf:
+        fig.savefig(buf, format='png')
+        ratio1 = Image.open(buf)
+        ratio1.load()
+
+    fig, ax = plt.subplots()
+    ax.plot([1, 2, 3])
+    fig.canvas._set_device_pixel_ratio(2)
+    with io.BytesIO() as buf:
+        fig.savefig(buf, format='png')
+        ratio2 = Image.open(buf)
+        ratio2.load()
+
+    assert ratio1 == ratio2
+
+
 def test_figure_repr():
     fig = plt.figure(figsize=(10, 20), dpi=10)
     assert repr(fig) == "<Figure size 100x200 with 0 Axes>"