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Merge pull request #16090 from greglucas/pcolormesh_snapping
Change pcolormesh snapping (fixes alpha colorbar/grid issues) [AGG]
2 parents 5a9191b + f31c51a commit d85adce

19 files changed

+156
-9
lines changed

‎doc/users/next_whats_new/pcolormesh_alpha_improvement.rst‎

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pcolormesh has improved transparency handling by enabling snapping
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------------------------------------------------------------------
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Due to how the snapping keyword argument was getting passed to the AGG backend,
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previous versions of Matplotlib would appear to show lines between the grid
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edges of a mesh with transparency. This version now applies snapping
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by default. To restore the old behavior (e.g., for test images), you may set
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:rc:`pcolormesh.snap` to `False`.
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.. plot::
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import matplotlib.pyplot as plt
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import numpy as np
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# Use old pcolormesh snapping values
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plt.rcParams['pcolormesh.snap'] = False
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fig, ax = plt.subplots()
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xx, yy = np.meshgrid(np.arange(10), np.arange(10))
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z = (xx + 1) * (yy + 1)
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mesh = ax.pcolormesh(xx, yy, z, shading='auto', alpha=0.5)
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fig.colorbar(mesh, orientation='vertical')
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ax.set_title('Before (pcolormesh.snap = False)')
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Note that there are lines between the grid boundaries of the main plot which
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are not the same transparency. The colorbar also shows these lines when a
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transparency is added to the colormap because internally it uses pcolormesh
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to draw the colorbar. With snapping on by default (below), the lines
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at the grid boundaries disappear.
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.. plot::
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import matplotlib.pyplot as plt
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import numpy as np
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fig, ax = plt.subplots()
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xx, yy = np.meshgrid(np.arange(10), np.arange(10))
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z = (xx + 1) * (yy + 1)
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mesh = ax.pcolormesh(xx, yy, z, shading='auto', alpha=0.5)
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fig.colorbar(mesh, orientation='vertical')
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ax.set_title('After (default: pcolormesh.snap = True)')

‎lib/matplotlib/axes/_axes.py‎

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@@ -6090,6 +6090,8 @@ def pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
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collection = mcoll.QuadMesh(Nx - 1, Ny - 1, coords,
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antialiased=antialiased, shading=shading,
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**kwargs)
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snap = kwargs.get('snap', rcParams['pcolormesh.snap'])
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collection.set_snap(snap)
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collection.set_alpha(alpha)
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collection.set_array(C)
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collection.set_cmap(cmap)

‎lib/matplotlib/collections.py‎

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@@ -2036,6 +2036,7 @@ def draw(self, renderer):
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transOffset = transOffset.get_affine()
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gc = renderer.new_gc()
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gc.set_snap(self.get_snap())
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self._set_gc_clip(gc)
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gc.set_linewidth(self.get_linewidth()[0])
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‎lib/matplotlib/rcsetup.py‎

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@@ -1113,6 +1113,7 @@ def _convert_validator_spec(key, conv):
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## pcolor(mesh) props:
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"pcolor.shading": ["auto", "flat", "nearest", "gouraud"],
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"pcolormesh.snap": validate_bool,
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## patch props
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"patch.linewidth": validate_float, # line width in points

‎lib/matplotlib/tests/test_agg_filter.py‎

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@image_comparison(baseline_images=['agg_filter_alpha'],
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extensions=['png', 'pdf'])
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def test_agg_filter_alpha():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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ax = plt.axes()
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x, y = np.mgrid[0:7, 0:8]
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data = x**2 - y**2

‎lib/matplotlib/tests/test_axes.py‎

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@@ -731,6 +731,10 @@ def test_hexbin_pickable():
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@image_comparison(['hexbin_log.png'], style='mpl20')
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def test_hexbin_log():
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# Issue #1636 (and also test log scaled colorbar)
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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np.random.seed(19680801)
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n = 100000
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x = np.random.standard_normal(n)
@@ -992,6 +996,9 @@ def test_pcolorargs_5205():
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@image_comparison(['pcolormesh'], remove_text=True)
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def test_pcolormesh():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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n = 12
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x = np.linspace(-1.5, 1.5, n)
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y = np.linspace(-1.5, 1.5, n*2)
@@ -1014,6 +1021,9 @@ def test_pcolormesh():
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@image_comparison(['pcolormesh_alpha'], extensions=["png", "pdf"],
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remove_text=True)
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def test_pcolormesh_alpha():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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n = 12
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X, Y = np.meshgrid(
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np.linspace(-1.5, 1.5, n),
@@ -1046,6 +1056,9 @@ def test_pcolormesh_alpha():
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@image_comparison(['pcolormesh_datetime_axis.png'],
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remove_text=False, style='mpl20')
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def test_pcolormesh_datetime_axis():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig = plt.figure()
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fig.subplots_adjust(hspace=0.4, top=0.98, bottom=.15)
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base = datetime.datetime(2013, 1, 1)
@@ -1750,6 +1763,9 @@ def test_contour_hatching():
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@image_comparison(['contour_colorbar'], style='mpl20')
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def test_contour_colorbar():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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x, y, z = contour_dat()
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fig = plt.figure()
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@image_comparison(['hist2d', 'hist2d'], remove_text=True, style='mpl20')
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def test_hist2d():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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np.random.seed(0)
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# make it not symmetric in case we switch x and y axis
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x = np.random.randn(100)*2+5
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@image_comparison(['hist2d_transpose'], remove_text=True, style='mpl20')
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def test_hist2d_transpose():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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np.random.seed(0)
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# make sure the output from np.histogram is transposed before
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# passing to pcolorfast

‎lib/matplotlib/tests/test_colorbar.py‎

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@@ -101,6 +101,9 @@ def _colorbar_extension_length(spacing):
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'colorbar_extensions_shape_proportional.png'])
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def test_colorbar_extension_shape():
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"""Test rectangular colorbar extensions."""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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# Create figures for uniform and proportionally spaced colorbars.
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_colorbar_extension_shape('uniform')
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_colorbar_extension_shape('proportional')
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'colorbar_extensions_proportional.png'])
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def test_colorbar_extension_length():
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"""Test variable length colorbar extensions."""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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# Create figures for uniform and proportionally spaced colorbars.
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_colorbar_extension_length('uniform')
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_colorbar_extension_length('proportional')
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extensions=['png'], remove_text=True,
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savefig_kwarg={'dpi': 40})
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def test_colorbar_positioning(use_gridspec):
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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data = np.arange(1200).reshape(30, 40)
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levels = [0, 200, 400, 600, 800, 1000, 1200]
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@@ -232,6 +241,9 @@ def test_colorbarbase():
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@image_comparison(['colorbar_closed_patch'], remove_text=True)
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def test_colorbar_closed_patch():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig = plt.figure(figsize=(8, 6))
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ax1 = fig.add_axes([0.05, 0.85, 0.9, 0.1])
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ax2 = fig.add_axes([0.1, 0.65, 0.75, 0.1])

‎lib/matplotlib/tests/test_colors.py‎

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@@ -608,6 +608,9 @@ def _mask_tester(norm_instance, vals):
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@image_comparison(['levels_and_colors.png'])
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def test_cmap_and_norm_from_levels_and_colors():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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data = np.linspace(-2, 4, 49).reshape(7, 7)
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levels = [-1, 2, 2.5, 3]
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colors = ['red', 'green', 'blue', 'yellow', 'black']
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@image_comparison(baseline_images=['boundarynorm_and_colorbar'],
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extensions=['png'])
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def test_boundarynorm_and_colorbarbase():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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# Make a figure and axes with dimensions as desired.
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fig = plt.figure()

‎lib/matplotlib/tests/test_constrainedlayout.py‎

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@@ -51,6 +51,9 @@ def test_constrained_layout2():
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@image_comparison(['constrained_layout3.png'])
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def test_constrained_layout3():
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"""Test constrained_layout for colorbars with subplots"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True)
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for nn, ax in enumerate(axs.flat):
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pcm = example_pcolor(ax, fontsize=24)
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@image_comparison(['constrained_layout4'])
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def test_constrained_layout4():
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"""Test constrained_layout for a single colorbar with subplots"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True)
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for ax in axs.flat:
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pcm = example_pcolor(ax, fontsize=24)
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Test constrained_layout for a single colorbar with subplots,
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colorbar bottom
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"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True)
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for ax in axs.flat:
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pcm = example_pcolor(ax, fontsize=24)
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@image_comparison(['constrained_layout6.png'])
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def test_constrained_layout6():
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"""Test constrained_layout for nested gridspecs"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig = plt.figure(constrained_layout=True)
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gs = fig.add_gridspec(1, 2, figure=fig)
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gsl = gs[0].subgridspec(2, 2)
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@image_comparison(['constrained_layout8.png'])
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def test_constrained_layout8():
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"""Test for gridspecs that are not completely full"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig = plt.figure(figsize=(10, 5), constrained_layout=True)
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gs = gridspec.GridSpec(3, 5, figure=fig)
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axs = []
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@image_comparison(['constrained_layout9.png'])
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def test_constrained_layout9():
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"""Test for handling suptitle and for sharex and sharey"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True,
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sharex=False, sharey=False)
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for ax in axs.flat:
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@image_comparison(['constrained_layout11.png'])
177195
def test_constrained_layout11():
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"""Test for multiple nested gridspecs"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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179200
fig = plt.figure(constrained_layout=True, figsize=(13, 3))
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gs0 = gridspec.GridSpec(1, 2, figure=fig)
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gsl = gridspec.GridSpecFromSubplotSpec(1, 2, gs0[0])
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@image_comparison(['constrained_layout11rat.png'])
196217
def test_constrained_layout11rat():
197218
"""Test for multiple nested gridspecs with width_ratios"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig = plt.figure(constrained_layout=True, figsize=(10, 3))
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gs0 = gridspec.GridSpec(1, 2, figure=fig, width_ratios=[6, 1])
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gsl = gridspec.GridSpecFromSubplotSpec(1, 2, gs0[0])
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@image_comparison(['constrained_layout13.png'], tol=2.e-2)
237261
def test_constrained_layout13():
238262
"""Test that padding works."""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True)
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for ax in axs.flat:
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pcm = example_pcolor(ax, fontsize=12)
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@image_comparison(['constrained_layout14.png'])
247274
def test_constrained_layout14():
248275
"""Test that padding works."""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(2, 2, constrained_layout=True)
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for ax in axs.flat:
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pcm = example_pcolor(ax, fontsize=12)
@@ -374,6 +404,8 @@ def test_colorbar_location():
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Test that colorbar handling is as expected for various complicated
375405
cases...
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"""
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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fig, axs = plt.subplots(4, 5, constrained_layout=True)
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for ax in axs.flat:

‎lib/matplotlib/tests/test_contour.py‎

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@@ -137,6 +137,9 @@ def test_contour_labels_size_color():
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@image_comparison(['contour_manual_colors_and_levels.png'], remove_text=True)
139139
def test_given_colors_levels_and_extends():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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_, axs = plt.subplots(2, 4)
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data = np.arange(12).reshape(3, 4)
@@ -318,6 +321,9 @@ def test_clabel_zorder(use_clabeltext, contour_zorder, clabel_zorder):
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@image_comparison(['contour_log_extension.png'],
319322
remove_text=True, style='mpl20')
320323
def test_contourf_log_extension():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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# Test that contourf with lognorm is extended correctly
322328
fig = plt.figure(figsize=(10, 5))
323329
fig.subplots_adjust(left=0.05, right=0.95)
@@ -357,6 +363,9 @@ def test_contourf_log_extension():
357363
# tolerance is because image changed minutely when tick finding on
358364
# colorbars was cleaned up...
359365
def test_contour_addlines():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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360369
fig, ax = plt.subplots()
361370
np.random.seed(19680812)
362371
X = np.random.rand(10, 10)*10000
@@ -371,6 +380,9 @@ def test_contour_addlines():
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@image_comparison(baseline_images=['contour_uneven'],
372381
extensions=['png'], remove_text=True, style='mpl20')
373382
def test_contour_uneven():
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# Remove this line when this test image is regenerated.
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plt.rcParams['pcolormesh.snap'] = False
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374386
z = np.arange(24).reshape(4, 6)
375387
fig, axs = plt.subplots(1, 2)
376388
ax = axs[0]

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