title: Fill between x and baseline x position in Matplotlib
body: <p>I'm looking for a way to use fill_between in matplotlib to shade between x1 and x2 as opposed to y1 and y2. </p>
  
  <p>I have a series of log plots, with depth on the Y axis, and the measured variable on the x axis and would like to shade to the left or right, as opposed to above or below, of the plotted line.     </p>
  
  <p>I'm sure this should be possible with fill_between but cant make it work.</p>
  
  <p>As an example:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  import matplotlib.gridspec as gridspec
  
  
  gs = gridspec.GridSpec(3, 3)
  ax1 = plt.subplot(gs[0, :])
  ax2 = plt.subplot(gs[1:, 1])
  
  y=np.random.uniform(0,1,30)
  x=np.arange(30)
  
  ax1.set_ylabel('Plot 1')
  ax1.plot(x,y)
  ax1.fill_between(x,y,0.5,where=y&gt;0.5,interpolate=True)
  
  ax2.set_ylabel('Plot 2')
  ax2.plot(y,x)
  ax2.set_ylim(30,0)
  
  plt.show()
  </code></pre>
  
  <p>I have attached an image of what this produces:
  Essentially i want to plot something like plot 1 in the plot 2 position
  <img src="https://i.stack.imgur.com/roeiP.png" alt="enter image description here"></p>
  
  <p>Thankyou for any suggestions </p>