Fix #319 by nudging the first coordinate of some shapes. (#320)

* Fix #319 by nudging the first coordinate of some shapes.

* Improve efficiency of the fix for #319.

svglib/svglib.py

@@ -967,8 +967,9 @@ def convert_length_attrs(self, node, *attrs, em_base=DEFAULT_FONT_SIZE, **kwargs
         ]
 
     def convertLine(self, node):
-        x1, y1, x2, y2 = self.convert_length_attrs(node, 'x1', 'y1', 'x2', 'y2')
-        return Line(x1, y1, x2, y2)
+        points = self.convert_length_attrs(node, 'x1', 'y1', 'x2', 'y2')
+        nudge_points(points)
+        return Line(*points)
 
     def convertRect(self, node):
         x, y, width, height, rx, ry = self.convert_length_attrs(
@@ -999,6 +1000,7 @@ def convertPolyline(self, node):
             # Odd number of coordinates or no coordinates, invalid polyline
             return None
 
+        nudge_points(points)
         polyline = PolyLine(points)
         self.applyStyleOnShape(polyline, node)
         has_fill = self.attrConverter.findAttr(node, 'fill') not in ('', 'none')
@@ -1024,6 +1026,7 @@ def convertPolygon(self, node):
         if len(points) % 2 != 0 or len(points) == 0:
             # Odd number of coordinates or no coordinates, invalid polygon
             return None
+        nudge_points(points)
         shape = Polygon(points)
 
         return shape
@@ -1462,6 +1465,26 @@ def svg2rlg(path, resolve_entities=False, **kwargs):
     return drawing
 
 
+def nudge_points(points):
+    """ Nudge first coordinate if all coordinate pairs are identical.
+
+    This works around reportlab's decision to hide shapes of size zero, even
+    when the stroke should be visible.
+    """
+    if not points:
+        return
+    if len(points) < 4:
+        return
+    x = points[0]
+    y = points[1]
+    for i in range(2, len(points)-1, 2):
+        if x != points[i] or y != points[i+1]:
+            break
+    else:
+        # All points were identical, so we nudge.
+        points[0] *= 1.0000001
+
+
 def load_svg_file(path, resolve_entities=False):
     parser = etree.XMLParser(
         remove_comments=True, recover=True, resolve_entities=resolve_entities

tests/test_basic.py

@@ -16,7 +16,7 @@
 from tempfile import NamedTemporaryFile
 
 from reportlab.graphics.shapes import (
-    _CLOSEPATH, _CURVETO, _LINETO, _MOVETO, Group, Path, Polygon, PolyLine, Rect,
+    _CLOSEPATH, _CURVETO, _LINETO, _MOVETO, Group, Path, Polygon, PolyLine, Rect, Line,
 )
 from reportlab.lib import colors
 from reportlab.lib.units import cm, inch
@@ -702,6 +702,30 @@ def test_strokewidth_0(self):
         assert rect.strokeColor is None
 
 
+class TestLineNode:
+    def test_length_zero(self):
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<line stroke="#000000" x1="10" y1="20" x2="10" y2="20" />'
+        ))
+        line = converter.convertLine(node)
+        assert isinstance(line, Line)
+
+        # Force a slight change in the first coordinate, so it's not invisible.
+        assert line.x1 != 10
+
+    def test_length_not_zero(self):
+        """ No change needed when length is not zero. """
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<line stroke="#000000" x1="10" y1="20" x2="10" y2="30" />'
+        ))
+        line = converter.convertLine(node)
+        assert isinstance(line, Line)
+
+        assert line.x1 == 10
+
+
 class TestPolylineNode:
     def test_filling(self):
         converter = svglib.Svg2RlgShapeConverter(None)
@@ -722,6 +746,50 @@ def test_filling(self):
         assert group.contents[0].fillColor == colors.white
         assert isinstance(group.contents[1], PolyLine)
 
+    def test_length_zero(self):
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<polyline fill="none" stroke="#000000" '
+            'points="10,50,10,50" />'
+        ))
+        polyline = converter.convertPolyline(node)
+        assert isinstance(polyline, PolyLine)
+
+        # Force a slight change in the first coordinate, so it's not invisible.
+        assert polyline.points[0] != 10
+
+    def test_odd_length(self):
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<polyline fill="none" stroke="#000000" '
+            'points="10,50,10,50,10" />'
+        ))
+        polyline = converter.convertPolyline(node)
+        assert polyline is None
+
+
+class TestPolygonNode:
+    def test_length_zero(self):
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<polygon fill="none" stroke="#000000" '
+            'points="10,50,10,50" />'
+        ))
+        polygon = converter.convertPolygon(node)
+        assert isinstance(polygon, Polygon)
+
+        # Force a slight change in the first coordinate, so it's not invisible.
+        assert polygon.points[0] != 10
+
+    def test_odd_length(self):
+        converter = svglib.Svg2RlgShapeConverter(None)
+        node = svglib.NodeTracker(etree.XML(
+            '<polygon fill="none" stroke="#000000" '
+            'points="10,50,10,50,10" />'
+        ))
+        polygon = converter.convertPolygon(node)
+        assert polygon is None
+
 
 class TestUseNode:
     def test_use(self, drawing_source=None):