Automatically load PGF components

takimata · takimata · commit d3ad76faa9d0 · 2021-08-22T21:30:44.000+02:00
diff --git a/lib/matplotlib/artist.py b/lib/matplotlib/artist.py
@@ -677,16 +677,6 @@ def set_sketch_params(self, scale=None, length=None, randomness=None):
         """
         Set the sketch parameters.
 
-        Requires the following preamble when using the PGF backend::
-
-            \\usepgfmodule{decorations}
-            \\usepgflibrary{decorations.pathmorphing}
-
-        This also applies to PGF backend + PDF output, where this must be added
-        to *pgf.preamble* manually. The PGF backend uses the *randomness*
-        argument as a seed and not as described below. Pass the same seed to
-        obtain the same random shape.
-
         Parameters
         ----------
         scale : float, optional
@@ -700,6 +690,9 @@ def set_sketch_params(self, scale=None, length=None, randomness=None):
             The scale factor by which the length is shrunken or
             expanded (default 16.0)
 
+            The PGF backend uses this argument as an RNG seed and not as
+            described above. Using the same seed yields the same random shape.
+
             .. ACCEPTS: (scale: float, length: float, randomness: float)
         """
         if scale is None:
diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
@@ -612,6 +612,9 @@ def _print_pgf_path(self, gc, path, transform, rgbFace=None):
             # same shape on multiple sketched lines
             scale, length, randomness = sketch_params
             if scale is not None:
+                # PGF guarantees that repeated loading is a no-op
+                writeln(self.fh, r"\usepgfmodule{decorations}")
+                writeln(self.fh, r"\usepgflibrary{decorations.pathmorphing}")
                 writeln(self.fh, r"\pgfkeys{/pgf/decoration/.cd, "
                         f"segment length = {(length * f):f}in, "
                         f"amplitude = {(scale * f):f}in}}")
diff --git a/lib/matplotlib/tests/test_backend_pgf.py b/lib/matplotlib/tests/test_backend_pgf.py
@@ -354,6 +354,8 @@ def test_sketch_params():
 
     baseline = r"""\pgfpathmoveto{\pgfqpoint{0.375000in}{0.300000in}}%
 \pgfpathlineto{\pgfqpoint{2.700000in}{2.700000in}}%
+\usepgfmodule{decorations}%
+\usepgflibrary{decorations.pathmorphing}%
 \pgfkeys{/pgf/decoration/.cd, """ \
     r"""segment length = 0.300000in, amplitude = 0.050000in}%
 \pgfmathsetseed{42}%
