Fixed how write handles opacity in SVG output (#429)

Inkscape does not support alpha in `stroke` attribute (e.g. `stroke="#ff00007f"`). The attribute `stroke-opacity` must be used instead.

Fixes #422

CHANGELOG.md

@@ -10,7 +10,7 @@ Release date: UNRELEASED
 
 ### Bug fixes
 
-* ...
+* Fixed issue with `write` where layer opacity was included in the `stroke` attribute instead of using `stroke-opacity`, which, although compliant, was not compatible with Inkscape (#429)
 
 ### Other changes
 

tests/test_files.py

@@ -428,6 +428,18 @@ def test_write_svg_svg_props_unknown_namespace(capsys):
     assert 'unknown:version="1.1.0"' not in capsys.readouterr().out
 
 
+def test_write_opacity_100pct(capsys):
+    vpype_cli.execute("line 0 0 10 10 color red write -f svg -")
+    assert 'stroke="#ff0000"' in capsys.readouterr().out
+
+
+def test_write_opacity_50pct(capsys):
+    vpype_cli.execute("line 0 0 10 10 color '#ff00007f' write -f svg -")
+    output = capsys.readouterr().out
+    assert 'stroke="#ff0000"' in output
+    assert 'stroke-opacity="0.498"' in output
+
+
 def test_read_no_fail():
     with pytest.raises(click.BadParameter):
         vpype_cli.execute("read doesnotexist.svg")

vpype/io.py

@@ -748,21 +748,24 @@ def write_svg(
         group = inkscape.layer(label=label)
         group.attribs["fill"] = "none"
 
+        color = Color("black")
         if color_mode == "layer" or (
             color_mode == "default" and not layer.property_exists(METADATA_FIELD_COLOR)
         ):
-            group.attribs["stroke"] = METADATA_DEFAULT_COLOR_SCHEME[
+            color = METADATA_DEFAULT_COLOR_SCHEME[
                 color_idx % len(METADATA_DEFAULT_COLOR_SCHEME)
             ]
             color_idx += 1
         elif color_mode == "default":
-            group.attribs["stroke"] = str(layer.property(METADATA_FIELD_COLOR))
+            color = Color(layer.property(METADATA_FIELD_COLOR))
 
             # we want to avoid a subsequent layer whose color is undefined to have its color
             # affected by whether or not previous layer have their color defined
             color_idx += 1
-        elif color_mode == "none":
-            group.attribs["stroke"] = "black"
+
+        group.attribs["stroke"] = color.as_rgb_hes()
+        if color.alpha < 255:
+            group.attribs["stroke-opacity"] = f"{color.alpha/255:.3f}"
         group.attribs["style"] = "display:inline"
         group.attribs["id"] = f"layer{layer_id}"
         if layer.property_exists(METADATA_FIELD_PEN_WIDTH):

vpype/metadata.py

@@ -60,6 +60,10 @@ def as_hex(self) -> str:
         """Return a standard, hexadecimal representation of the instance."""
         return svgelements.Color(self.red, self.green, self.blue, self.alpha).hex
 
+    def as_rgb_hes(self) -> str:
+        """Return a standard, hexadecimal representation of the instance, ignoring alpha."""
+        return svgelements.Color(self.red, self.green, self.blue).hexrgb
+
     def __str__(self) -> str:
         return self.as_hex()