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import numpy as np

import matplotlib.pyplot as plt

from matplotlib.testing.decorators import image_comparison

@image_comparison(baseline_images=['agg_filter_alpha'],

extensions=['png', 'pdf'])

def test_agg_filter_alpha():

# Remove this line when this test image is regenerated.

plt.rcParams['pcolormesh.snap'] = False

ax = plt.axes()

x, y = np.mgrid[0:7, 0:8]

data = x**2 - y**2

mesh = ax.pcolormesh(data, cmap='Reds', zorder=5)

def manual_alpha(im, dpi):

im[:, :, 3] *= 0.6

print('CALLED')

return im, 0, 0

# Note: Doing alpha like this is not the same as setting alpha on

# the mesh itself. Currently meshes are drawn as independent patches,

# and we see fine borders around the blocks of color. See the SO

# question for an example: https://stackoverflow.com/q/20678817/

mesh.set_agg_filter(manual_alpha)

# Currently we must enable rasterization for this to have an effect in

# the PDF backend.

mesh.set_rasterized(True)

ax.plot([0, 4, 7], [1, 3, 8])