Simplify binary data handling in ps backend.

- bytes.hex() can now perform linewrapping itself, so use that in
  draw_image.
- draw_gouraud_triangles can rely on PostScript's hexstring format
  (`<...>` instead of `(...)`) and thus on bytes.hex() too.  This makes
  _quote_ps_string fully unused, thus tweak the deprecation of
  quote_ps_string.

Also add a test for PostScript Gouraud shading, which was previously not
covered at all.

Author: anntzer

lib/matplotlib/backends/backend_ps.py

@@ -91,10 +91,6 @@ def _nums_to_str(*args):
 
 @_api.deprecated("3.6", alternative="Vendor the code")
 def quote_ps_string(s):
-    return _quote_ps_string(s)
-
-
-def _quote_ps_string(s):
     """
     Quote dangerous characters of S for use in a PostScript string constant.
     """
@@ -447,17 +443,7 @@ def draw_image(self, gc, x, y, im, transform=None):
         h, w = im.shape[:2]
         imagecmd = "false 3 colorimage"
         data = im[::-1, :, :3]  # Vertically flipped rgb values.
-        # data.tobytes().hex() has no spaces, so can be linewrapped by simply
-        # splitting data every nchars. It's equivalent to textwrap.fill only
-        # much faster.
-        nchars = 128
-        data = data.tobytes().hex()
-        hexlines = "\n".join(
-            [
-                data[n * nchars:(n + 1) * nchars]
-                for n in range(math.ceil(len(data) / nchars))
-            ]
-        )
+        hexdata = data.tobytes().hex("\n", -64)  # Linewrap to 128 chars.
 
         if transform is None:
             matrix = "1 0 0 1 0 0"
@@ -479,7 +465,7 @@ def draw_image(self, gc, x, y, im, transform=None):
 {{
 currentfile DataString readhexstring pop
 }} bind {imagecmd}
-{hexlines}
+{hexdata}
 grestore
 """)
 
@@ -737,13 +723,13 @@ def draw_gouraud_triangles(self, gc, points, colors, trans):
         xmin, ymin = points_min
         xmax, ymax = points_max
 
-        streamarr = np.empty(
+        data = np.empty(
             shape[0] * shape[1],
             dtype=[('flags', 'u1'), ('points', '2>u4'), ('colors', '3u1')])
-        streamarr['flags'] = 0
-        streamarr['points'] = (flat_points - points_min) * factor
-        streamarr['colors'] = flat_colors[:, :3] * 255.0
-        stream = _quote_ps_string(streamarr.tobytes())
+        data['flags'] = 0
+        data['points'] = (flat_points - points_min) * factor
+        data['colors'] = flat_colors[:, :3] * 255.0
+        hexdata = data.tobytes().hex("\n", -64)  # Linewrap to 128 chars.
 
         self._pswriter.write(f"""\
 gsave
@@ -754,7 +740,9 @@ def draw_gouraud_triangles(self, gc, points, colors, trans):
    /BitsPerFlag 8
    /AntiAlias true
    /Decode [ {xmin:g} {xmax:g} {ymin:g} {ymax:g} 0 1 0 1 0 1 ]
-   /DataSource ({stream})
+   /DataSource <
+{hexdata}
+>
 >>
 shfill
 grestore