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Make the frame size of animation writers be the canvas size rather than the figure size #32194

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Make the frame size of animation writers be the canvas size rather than the figure size #32194

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11 changes: 7 additions & 4 deletions lib/matplotlib/animation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -173,12 +173,12 @@ def setup(self, fig, outfile, dpi=None):
if dpi is None:
dpi = self.fig.dpi
self.dpi = dpi
fig.set_dpi(self.dpi)

@property
def frame_size(self):
"""A tuple ``(width, height)`` in pixels of a movie frame."""
w, h = self.fig.get_size_inches()
return int(w * self.dpi), int(h * self.dpi)
return self.fig.canvas.get_width_height()

def _supports_transparency(self):
"""
Expand Down Expand Up @@ -293,15 +293,17 @@ def __init__(self, fps=5, codec=None, bitrate=None, extra_args=None,
self.extra_args = extra_args

def _adjust_frame_size(self):
wo, ho = self.frame_size # in pixels, so need to convert to inches
wo /= self.dpi
ho /= self.dpi
if self.codec == 'h264':
wo, ho = self.fig.get_size_inches()
w, h = adjusted_figsize(wo, ho, self.dpi, 2)

@QuLogic QuLogic Aug 10, 2026

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What about the calculation in adjusted_figsize?

if (wo, ho) != (w, h):
self.fig.set_size_inches(w, h, forward=True)
_log.info('figure size in inches has been adjusted '
'from %s x %s to %s x %s', wo, ho, w, h)
else:
w, h = self.fig.get_size_inches()
w, h = wo, ho
_log.debug('frame size in pixels is %s x %s', *self.frame_size)
return w, h

Expand Down Expand Up @@ -411,6 +413,7 @@ def setup(self, fig, outfile, dpi=None, frame_prefix=None):
if dpi is None:
dpi = self.fig.dpi
self.dpi = dpi
fig.set_dpi(self.dpi)
self._adjust_frame_size()

if frame_prefix is None:
Expand Down
13 changes: 13 additions & 0 deletions lib/matplotlib/tests/test_animation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,19 @@ def test_null_movie_writer(anim):
assert writer._count == anim._save_count


def test_frame_size():
# Test that the frame size is the canvas size and not the figure size
fig = plt.figure(figsize=(1, 2.03), dpi=100)
assert fig.bbox.height < 203 # due to floating-point precision
assert fig.canvas.get_width_height() == (100, 203)

anim = animation.FuncAnimation(fig, lambda frame: tuple(), frames=1)
writer = NullMovieWriter()
anim.save("unused.null", dpi=100, writer=writer)

assert writer.frame_size == fig.canvas.get_width_height()


@pytest.mark.parametrize('anim', [dict(klass=dict)], indirect=['anim'])
def test_animation_delete(anim):
if platform.python_implementation() == 'PyPy':
Expand Down
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