From 76e2f4e0eb1c990f84ce87cf58bd134ea20e029e Mon Sep 17 00:00:00 2001
From: Antoine Beyeler <49431240+abey79@users.noreply.github.com>
Date: Sun, 27 Mar 2022 14:49:26 +0200
Subject: [PATCH] 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        |  2 +-
 tests/test_files.py | 12 ++++++++++++
 vpype/io.py         | 11 +++++++----
 vpype/metadata.py   |  4 ++++
 4 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ea21256b..d11ada14 100644
--- a/CHANGELOG.md
+++ b/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
 
diff --git a/tests/test_files.py b/tests/test_files.py
index 4568f3e2..03f317b6 100644
--- a/tests/test_files.py
+++ b/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")
diff --git a/vpype/io.py b/vpype/io.py
index d5e1688d..c7be4945 100644
--- a/vpype/io.py
+++ b/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):
diff --git a/vpype/metadata.py b/vpype/metadata.py
index 37684a7a..ea885d80 100644
--- a/vpype/metadata.py
+++ b/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()