From 311108f779e58c728e769f6eaaecd7719e805d11 Mon Sep 17 00:00:00 2001
From: Darren Burns <darrenb900@gmail.com>
Date: Thu, 20 Oct 2022 09:47:03 +0100
Subject: [PATCH] Animating alpha colors

---
 sandbox/darren/color_animate.css |  0
 sandbox/darren/color_animate.py  | 22 ++++++++++++++++++++++
 sandbox/darren/just_a_box.py     | 23 +++++++++++++++--------
 src/textual/color.py             | 18 +++++++++++++-----
 4 files changed, 50 insertions(+), 13 deletions(-)
 create mode 100644 sandbox/darren/color_animate.css
 create mode 100644 sandbox/darren/color_animate.py

diff --git a/sandbox/darren/color_animate.css b/sandbox/darren/color_animate.css
new file mode 100644
index 000000000..e69de29bb
diff --git a/sandbox/darren/color_animate.py b/sandbox/darren/color_animate.py
new file mode 100644
index 000000000..fb5227d76
--- /dev/null
+++ b/sandbox/darren/color_animate.py
@@ -0,0 +1,22 @@
+from textual.app import App, ComposeResult
+from textual.color import Color
+from textual.widgets import Static
+
+START_COLOR = Color.parse("#FF0000EE")
+END_COLOR = Color.parse("#0000FF0F")
+
+
+class ColorAnimate(App):
+    def compose(self) -> ComposeResult:
+        box = Static("Hello, world", id="box")
+        box.styles.background = START_COLOR
+        self.box = box
+        yield box
+
+    def key_a(self):
+        self.animator.animate(self.box.styles, "background", END_COLOR, duration=2.0)
+
+
+app = ColorAnimate(css_path="color_animate.css")
+if __name__ == "__main__":
+    app.run()
diff --git a/sandbox/darren/just_a_box.py b/sandbox/darren/just_a_box.py
index fa2ee364d..b4bc98e46 100644
--- a/sandbox/darren/just_a_box.py
+++ b/sandbox/darren/just_a_box.py
@@ -2,19 +2,21 @@ from __future__ import annotations
 
 from textual.app import App, ComposeResult
 from textual.binding import Binding
+from textual.screen import Screen
 from textual.widgets import Static, Footer, Header
 
 
-class JustABox(App):
+class MainScreen(Screen):
+
     BINDINGS = [
         Binding(
             key="ctrl+t", action="text_fade_out", description="text-opacity fade out"
         ),
-        Binding(
-            key="o,f,w",
-            action="widget_fade_out",
-            description="opacity fade out",
-            key_display="o or f or w",
+        (
+            "o,f,w",
+            "widget_fade_out",
+            "opacity fade out",
+            # key_display="o or f or w",
         ),
     ]
 
@@ -25,11 +27,16 @@ class JustABox(App):
 
     def action_text_fade_out(self) -> None:
         box = self.query_one("#box1")
-        self.animator.animate(box.styles, "text_opacity", value=0.0, duration=1)
+        self.app.animator.animate(box.styles, "text_opacity", value=0.0, duration=1)
 
     def action_widget_fade_out(self) -> None:
         box = self.query_one("#box1")
-        self.animator.animate(box.styles, "opacity", value=0.0, duration=1)
+        self.app.animator.animate(box.styles, "opacity", value=0.0, duration=1)
+
+
+class JustABox(App):
+    def on_mount(self):
+        self.push_screen(MainScreen())
 
     def key_d(self):
         print(self.screen.styles.get_rules())
diff --git a/src/textual/color.py b/src/textual/color.py
index 16108e71d..5a60bb7b6 100644
--- a/src/textual/color.py
+++ b/src/textual/color.py
@@ -341,13 +341,15 @@ class Color(NamedTuple):
         r, g, b, _ = self
         return Color(r, g, b, alpha)
 
-    def blend(self, destination: Color, factor: float, alpha: float = 1) -> Color:
+    def blend(
+        self, destination: Color, factor: float, alpha: float | None = None
+    ) -> Color:
         """Generate a new color between two colors.
 
         Args:
             destination (Color): Another color.
             factor (float): A blend factor, 0 -> 1.
-            alpha (float | None): New alpha for result. Defaults to 1.
+            alpha (float | None): New alpha for result. Defaults to None.
 
         Returns:
             Color: A new color.
@@ -356,13 +358,19 @@ class Color(NamedTuple):
             return self
         elif factor == 1:
             return destination
-        r1, g1, b1, _ = self
-        r2, g2, b2, _ = destination
+        r1, g1, b1, a1 = self
+        r2, g2, b2, a2 = destination
+
+        if alpha is None:
+            new_alpha = a1 + (a2 - a1) * factor
+        else:
+            new_alpha = alpha
+
         return Color(
             int(r1 + (r2 - r1) * factor),
             int(g1 + (g2 - g1) * factor),
             int(b1 + (b2 - b1) * factor),
-            alpha,
+            new_alpha,
         )
 
     def __add__(self, other: object) -> Color: