Deprecate GraphicsContextPS.

The conversion functions (which is the only thing GraphicsContextPS
adds) are really internal to the PS format and can be done at the
renderer level instead, saving the need for an separate GraphicsContext
subclass.

Author: anntzer

doc/api/next_api_changes/deprecations/18687-AL.rst

@@ -0,0 +1,3 @@
+GraphicsContextPS
+~~~~~~~~~~~~~~~~~
+... is deprecated.  The PostScript backend now uses `.GraphicsContextBase`.

lib/matplotlib/backends/backend_ps.py

@@ -205,15 +205,29 @@ def set_linewidth(self, linewidth, store=True):
             if store:
                 self.linewidth = linewidth
 
+    @staticmethod
+    def _linejoin_cmd(linejoin):
+        # Support for directly passing integer values is for backcompat.
+        linejoin = {'miter': 0, 'round': 1, 'bevel': 2, 0: 0, 1: 1, 2: 2}[
+            linejoin]
+        return f"{linejoin:d} setlinejoin\n"
+
     def set_linejoin(self, linejoin, store=True):
         if linejoin != self.linejoin:
-            self._pswriter.write("%d setlinejoin\n" % linejoin)
+            self._pswriter.write(self._linejoin_cmd(linejoin))
             if store:
                 self.linejoin = linejoin
 
+    @staticmethod
+    def _linecap_cmd(linecap):
+        # Support for directly passing integer values is for backcompat.
+        linecap = {'butt': 0, 'round': 1, 'projecting': 2, 0: 0, 1: 1, 2: 2}[
+            linecap]
+        return f"{linecap:d} setlinecap\n"
+
     def set_linecap(self, linecap, store=True):
         if linecap != self.linecap:
-            self._pswriter.write("%d setlinecap\n" % linecap)
+            self._pswriter.write(self._linecap_cmd(linecap))
             if store:
                 self.linecap = linecap
 
@@ -397,10 +411,8 @@ def draw_markers(
         stroke = lw > 0 and alpha > 0
         if stroke:
             ps_cmd.append('%.1f setlinewidth' % lw)
-            jint = gc.get_joinstyle()
-            ps_cmd.append('%d setlinejoin' % jint)
-            cint = gc.get_capstyle()
-            ps_cmd.append('%d setlinecap' % cint)
+            ps_cmd.append(self._linejoin_cmd(gc.get_joinstyle()))
+            ps_cmd.append(self._linecap_cmd(gc.get_capstyle()))
 
         ps_cmd.append(self._convert_path(marker_path, marker_trans,
                                          simplify=False))
@@ -595,10 +607,6 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
 grestore
 """)
 
-    def new_gc(self):
-        # docstring inherited
-        return GraphicsContextPS()
-
     def draw_mathtext(self, gc, x, y, s, prop, angle):
         """Draw the math text using matplotlib.mathtext."""
         if debugPS:
@@ -703,10 +711,8 @@ def _draw_ps(self, ps, gc, rgbFace, fill=True, stroke=True, command=None):
 
         if mightstroke:
             self.set_linewidth(gc.get_linewidth())
-            jint = gc.get_joinstyle()
-            self.set_linejoin(jint)
-            cint = gc.get_capstyle()
-            self.set_linecap(cint)
+            self.set_linejoin(gc.get_joinstyle())
+            self.set_linecap(gc.get_capstyle())
             self.set_linedash(*gc.get_dashes())
             self.set_color(*gc.get_rgb()[:3])
         write('gsave\n')
@@ -759,6 +765,7 @@ def _is_transparent(rgb_or_rgba):
         return False
 
 
+@cbook.deprecated("3.4", alternative="GraphicsContextBase")
 class GraphicsContextPS(GraphicsContextBase):
     def get_capstyle(self):
         return {'butt': 0, 'round': 1, 'projecting': 2}[super().get_capstyle()]