Ensure opacity values are in range [0.0, 1.0]

docs/style_sheets.md

@@ -133,6 +133,8 @@ family, size, weight.
                         ``background-color: hsl(130, 95%, 10%);``
 ``color``               Color used for lines
 ``text-color``          Color for text
+``opacity``             Color opacity factor (``0.0`` - ``1.0``),
+                        applied to all colors
 ======================= =======================================
 ```
 

gaphor/core/styling/declarations.py

@@ -108,10 +108,18 @@ def parse_color(prop, value):
     "line-width",
     "vertical-spacing",
     "border-radius",
-    "opacity",
 )
 def parse_positive_number(prop, value) -> Optional[Number]:
-    if isinstance(value, number) and value > 0:
+    if isinstance(value, number) and value >= 0:
+        return value
+    return None
+
+
+@declarations.register(
+    "opacity",
+)
+def parse_factor(prop, value) -> Optional[Number]:
+    if isinstance(value, number) and 0 <= value <= 1:
         return value
     return None
 

gaphor/core/styling/tests/test_css.py

@@ -222,6 +222,26 @@ def test_line_style(css_value, result):
     assert props.get("line-style") == result
 
 
+@pytest.mark.parametrize(
+    "css_value,result",
+    [
+        [0.5, 0.5],
+        [0, 0.0],
+        [1, 1.0],
+        [-0.1, None],
+        [1.1, None],
+        ["wrong", None],
+    ],
+)
+def test_opacity(css_value, result):
+    css = f"mytype {{ opacity: {css_value} }}"
+
+    compiled_style_sheet = CompiledStyleSheet(css)
+    props = compiled_style_sheet.match(Node("mytype"))
+
+    assert props.get("opacity") == result
+
+
 def test_broken_line_style():
     # diagram css is missing the closing bracket
     css = "diagram { line-style: sloppy * { }"