Cache SVG use tags

Fix #1439.

tests/draw/svg/test_defs.py

@@ -0,0 +1,40 @@
+"""
+    weasyprint.tests.test_draw.svg.test_defs
+    ----------------------------------------
+
+    Test how SVG definitions are drawn.
+
+"""
+
+from ...testing_utils import assert_no_logs
+from .. import assert_pixels
+
+
+@assert_no_logs
+def test_use():
+    assert_pixels('use', 10, 10, '''
+        RRRRR_____
+        RRRRR_____
+        __________
+        ___RRRRR__
+        ___RRRRR__
+        __________
+        _____RRRRR
+        _____RRRRR
+        __________
+        __________
+    ''', '''
+      <style>
+        @page { size: 10px }
+        svg { display: block }
+      </style>
+      <svg width="10px" height="10px" xmlns="http://www.w3.org/2000/svg"
+           xlink="http://www.w3.org/1999/xlink">
+        <defs>
+          <rect id="rectangle" width="5" height="2" fill="red" />
+        </defs>
+        <use xlink:href="#rectangle" />
+        <use xlink:href="#rectangle" x="3" y="3" />
+        <use xlink:href="#rectangle" x="5" y="6" />
+      </svg>
+    ''')

weasyprint/svg/__init__.py

@@ -294,6 +294,8 @@ def __init__(self, bytestring_svg, url):
         self.patterns = {}
         self.paths = {}
 
+        self.use_cache = {}
+
         self.cursor_position = [0, 0]
         self.cursor_d_position = [0, 0]
         self.text_path_width = 0

weasyprint/svg/defs.py

@@ -27,10 +27,15 @@ def use(svg, node, font_size):
 
     parsed_url = parse_url(node.get_href())
     if parsed_url.fragment and not parsed_url.path:
-        try:
-            tree = svg.tree.get_child(parsed_url.fragment).copy()
-        except AttributeError:
-            return
+        if parsed_url.fragment in svg.use_cache:
+            tree = svg.use_cache[parsed_url.fragment].copy()
+        else:
+            try:
+                tree = svg.tree.get_child(parsed_url.fragment).copy()
+            except AttributeError:
+                return
+            else:
+                svg.use_cache[parsed_url.fragment] = tree
     else:
         url = parsed_url.geturl()
         try: