tint fix

Author: willmcgugan

src/textual/color.py

@@ -399,6 +399,31 @@ def blend(
             new_alpha,
         )
 
+    @lru_cache(maxsize=1024)
+    def tint(self, color: Color) -> Color:
+        """Apply a tint to a color.
+
+        Similar to blend, but combines color and alpha.
+
+        Args:
+            color: A color with alpha component.
+
+        Returns:
+            New color
+        """
+        r2, g2, b2, a2, ansi2 = color
+        if ansi2 is not None:
+            return color
+        r1, g1, b1, a1, ansi1 = self
+        if ansi1 is not None:
+            return color
+        return Color(
+            int(r1 + (r2 - r1) * a2),
+            int(g1 + (g2 - g1) * a2),
+            int(b1 + (b2 - b1) * a2),
+            a1,
+        )
+
     def __add__(self, other: object) -> Color:
         if isinstance(other, Color):
             return self.blend(other, other.a, 1.0)

src/textual/dom.py

@@ -1026,11 +1026,11 @@ def rich_style(self) -> Style:
             has_rule = styles.has_rule
             opacity *= styles.opacity
             if has_rule("background"):
-                text_background = (
-                    background + styles.background + styles.background_tint
+                text_background = background + styles.background.tint(
+                    styles.background_tint
                 )
                 background += (
-                    styles.background + styles.background_tint
+                    styles.background.tint(styles.background_tint)
                 ).multiply_alpha(opacity)
             else:
                 text_background = background
@@ -1119,7 +1119,7 @@ def background_colors(self) -> tuple[Color, Color]:
         for node in reversed(self.ancestors_with_self):
             styles = node.styles
             base_background = background
-            background += styles.background + styles.background_tint
+            background += styles.background.tint(styles.background_tint)
         return (base_background, background)
 
     @property
@@ -1135,7 +1135,7 @@ def _opacity_background_colors(self) -> tuple[Color, Color]:
             styles = node.styles
             base_background = background
             opacity *= styles.opacity
-            background += (styles.background + styles.background_tint).multiply_alpha(
+            background += styles.background.tint(styles.background_tint).multiply_alpha(
                 opacity
             )
         return (base_background, background)
@@ -1152,7 +1152,7 @@ def colors(self) -> tuple[Color, Color, Color, Color]:
         for node in reversed(self.ancestors_with_self):
             styles = node.styles
             base_background = background
-            background += styles.background + styles.background_tint
+            background += styles.background.tint(styles.background_tint)
             if styles.has_rule("color"):
                 base_color = color
                 if styles.auto_color:

tests/snapshot_tests/test_snapshots.py

@@ -2314,15 +2314,27 @@ def compose(self) -> ComposeResult:
 
 
 def test_background_tint(snap_compare):
+    """Test background tint with alpha."""
+
+    # The screen background is dark blue
+    # The vertical is 20% white
+    # With no background tint, the verticals will be a light blue
+    # With a 100% tint, the vertical should be 20% red plus the blue (i.e. purple)
+
+    # tl;dr you should see 4 bars, blue at the top, purple at the bottom, and two shades in betweenm
+
     class BackgroundTintApp(App):
         CSS = """
+        Screen {
+            background: rgb(0,0,100)
+        }
         Vertical {
-            background: $panel;
+            background: rgba(255,255,255,0.2);
         }
-        #tint1 { background-tint: $foreground 0%; }
-        #tint2 { background-tint: $foreground 33%; }
-        #tint3 { background-tint: $foreground 66%; }
-        #tint4 { background-tint: $foreground 100% }
+        #tint1 { background-tint: rgb(255,0,0) 0%; }
+        #tint2 { background-tint: rgb(255,0,0) 33%; }
+        #tint3 { background-tint: rgb(255,0,0) 66%; }
+        #tint4 { background-tint: rgb(255,0,0) 100% }
         """
 
         def compose(self) -> ComposeResult:

tests/test_color.py

@@ -265,3 +265,27 @@ def test_is_transparent():
     assert not Color(20, 20, 30, a=0.01).is_transparent
     assert not Color(20, 20, 30, a=1).is_transparent
     assert not Color(20, 20, 30, 0, ansi=1).is_transparent
+
+
+@pytest.mark.parametrize(
+    "base,tint,expected",
+    [
+        (
+            Color(0, 0, 0),
+            Color(10, 20, 30),
+            Color(10, 20, 30),
+        ),
+        (
+            Color(0, 0, 0, 0.5),
+            Color(255, 255, 255, 0.5),
+            Color(127, 127, 127, 0.5),
+        ),
+        (
+            Color(100, 0, 0, 0.2),
+            Color(0, 100, 0, 0.5),
+            Color(50, 50, 0, 0.2),
+        ),
+    ],
+)
+def test_tint(base: Color, tint: Color, expected: Color) -> None:
+    assert base.tint(tint) == expected