title: Matplotlib figsize behaving strange in WXAgg
body: <p>Im trying to resize a figure to A4 paper size to save it as pdf. This gives strange behavior when using WXAgg. Here is an example:</p>
  
  <pre><code>import matplotlib as mpl
  mpl.use("WXAgg")
  import numpy as np
  import matplotlib.pyplot as plt
  
  # data to plot
  x = np.arange(0, 10, 0.005)
  y = np.sin(x)
  
  # plot the data
  fig = plt.figure()
  ax = fig.add_axes([0,0,1,1])
  ax.plot(x, y)
  
  # resize figure and immediatly print it's size
  page_width, page_height = (8.2765, 11.70475) #A4
  fig.set_size_inches(page_width, page_height)
  print fig.get_size_inches()
  </code></pre>
  
  <p>The output I get is <code>[ 8.27  7.59]</code>, not as expected. When I comment out the <code>mpl.use("WXAgg")</code>, it works fine. The output then is <code>[  8.2765   11.70475]</code> as expected.</p>
  
  <p>EDIT: Apparently this has something to do with the size of the screen. I changed screens (plugged in a monitor to my laptop) and the output changed to <code>[ 8.27  9.39]</code></p>
  
  <p>What is happening here? And how do I get the right figure size with WXAgg?</p>
  
  <p>Some information about my system:</p>
  
  <ul>
  <li>OS: macOS High Sierra <code>10.13.1</code></li>
  <li>python: <code>2.7.13</code> </li>
  <li>Matplotlib: <code>2.2.3</code></li>
  </ul>