add option to disable automatic figure resizing

A user requested that there be an option to disable
automatic resizing to support certain workflows.

As accessing the actual backend instance is a bit awkward,
we expose this setting as an environment variable called
`MPLBACKEND_KITTY_SIZING`, named analogously to MPL's
`MPLBACKEND` variable used to select backends.

closes #3

README.md

@@ -9,7 +9,8 @@ To use it, add the directory containing this module to your
 `sys.path` or the `$PYTHONPATH`, or clone this repo into
 your python's `site-packages` directory.
 
-Then, initialize matplotlib like this:
+Then, initialize matplotlib either as follows or using the
+the `MPLBACKEND` environment variable:
 
 ```python
 import matplotlib
@@ -38,6 +39,10 @@ you can construct your figures as usual, and then call
 `plt.show()` to render them to your terminal. This
 works from both a repl and when running scripts.
 
+Figures are resized to the size of your terminal by default.
+If you'd rather control the sizing of figures manually,
+set the `MPLBACKEND_KITTY_SIZING` environment variable to `manual`.
+
 Internally, this backend is somewhat based on matplotlib's
 IPython support: it's a hybrid of image and GUI backend types.
 It works by using matplotlib's `Agg` backend to render the

__init__.py

@@ -31,21 +31,25 @@ def f(*args, output=True, **kwargs):
         return f
 
     def show(self):
-        tput = __class__._run('tput')
+
         icat = __class__._run('kitty', '+kitten', 'icat')
 
-        # gather terminal dimensions
-        rows = int(tput('lines'))
-        px = icat('--print-window-size')
-        px = list(map(int, px.split('x')))
+        if os.environ.get('MPLBACKEND_KITTY_SIZING', 'automatic') != 'manual':
+
+            tput = __class__._run('tput')
+
+            # gather terminal dimensions
+            rows = int(tput('lines'))
+            px = icat('--print-window-size')
+            px = list(map(int, px.split('x')))
 
-        # account for post-display prompt scrolling
-        # 3 line shift for [\n, <matplotlib.axes…, >>>] after the figure
-        px[1] -= int(3*(px[1]/rows))
+            # account for post-display prompt scrolling
+            # 3 line shift for [\n, <matplotlib.axes…, >>>] after the figure
+            px[1] -= int(3*(px[1]/rows))
 
-        # resize figure to terminal size & aspect ratio
-        dpi = self.canvas.figure.dpi
-        self.canvas.figure.set_size_inches((px[0] / dpi, px[1] / dpi))
+            # resize figure to terminal size & aspect ratio
+            dpi = self.canvas.figure.dpi
+            self.canvas.figure.set_size_inches((px[0] / dpi, px[1] / dpi))
 
         with BytesIO() as buf:
             self.canvas.figure.savefig(buf, format='png', facecolor='#888888')