Speed up Path.iter_segments()

lazka · lazka · commit dcb5fbb51770 · 2018-12-22T17:53:02.000+01:00
Using the Gtk3Cairo backend with wire3d_animation_sgskip.py:

Before: 9.16 fps
After: 11.36 fps

The main speedup is from iterating and keeping the common non-curve
case simple and from converting the codes to int before comparing/hashing
them as using uint8 there is much slower for some reason.
diff --git a/lib/matplotlib/path.py b/lib/matplotlib/path.py
@@ -399,24 +399,26 @@ def iter_segments(self, transform=None, remove_nans=True, clip=None,
                                snap=snap, stroke_width=stroke_width,
                                simplify=simplify, curves=curves,
                                sketch=sketch)
-        vertices = cleaned.vertices
-        codes = cleaned.codes
-        len_vertices = vertices.shape[0]
 
         # Cache these object lookups for performance in the loop.
         NUM_VERTICES_FOR_CODE = self.NUM_VERTICES_FOR_CODE
         STOP = self.STOP
 
-        i = 0
-        while i < len_vertices:
-            code = codes[i]
-            if code == STOP:
-                return
+        vertices = iter(cleaned.vertices)
+        codes = iter(cleaned.codes)
+        for curr_vertices, code in zip(vertices, codes):
+            # int is a lot faster than uint8 when comparing/hashing
+            code_int = int(code)
+            if code_int == STOP:
+                break
+            extra_vertices = NUM_VERTICES_FOR_CODE[code_int] - 1
+            if extra_vertices:
+                for i in range(extra_vertices):
+                    next(codes)
+                    curr_vertices = np.append(curr_vertices, next(vertices))
+                yield curr_vertices, code
             else:
-                num_vertices = NUM_VERTICES_FOR_CODE[code]
-                curr_vertices = vertices[i:i+num_vertices].flatten()
                 yield curr_vertices, code
-                i += num_vertices
 
     def cleaned(self, transform=None, remove_nans=False, clip=None,
                 quantize=False, simplify=False, curves=False,
