Fix animation of offset with tuple and string

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Raise `ValueError` with improved error message when number of cells inserted using `DataTable.add_row` doesn't match the number of columns in the table https://github.com/Textualize/textual/pull/4742
 - Add `Tree.move_cursor` to programmatically move the cursor without selecting the node https://github.com/Textualize/textual/pull/4753
 - Added `Footer` component style handling of padding for the key/description https://github.com/Textualize/textual/pull/4651
+- Added ability to animate `widget.styles.offset` with `tuple` or `str` https://github.com/Textualize/textual/issues/3028
 
 ### Fixed
 

src/textual/css/scalar.py

@@ -362,6 +362,22 @@ def resolve(self, size: Size, viewport: Size) -> Offset:
             round(y.resolve(size, viewport)),
         )
 
+    @classmethod
+    def parse(cls, token: str) -> ScalarOffset:
+        """Create a scalar offset from a string.
+
+        Args:
+            token: String to parse (e.g. '1 2' or '1.0 2.0')
+
+        Returns:
+            New offset
+        """
+        x, y = token.split()
+        return cls(
+            Scalar.parse(x, Unit.WIDTH),
+            Scalar.parse(y, Unit.HEIGHT),
+        )
+
 
 NULL_SCALAR = ScalarOffset(Scalar.from_number(0), Scalar.from_number(0))
 

src/textual/css/styles.py

@@ -385,6 +385,13 @@ def __textual_animation__(
             # If destination is a number, we can convert that to a scalar
             if isinstance(value, (int, float)):
                 value = Scalar(value, Unit.CELLS, Unit.CELLS)
+            # If destination is a pair of numbers, we can convert it to a
+            # scalar offset
+            elif isinstance(value, tuple) and (
+                list(map(type, value)) == [int, int]
+                or list(map(type, value)) == [float, float]
+            ):
+                value = ScalarOffset.from_offset(value)
 
             # We can only animate to Scalar
             if not isinstance(value, (Scalar, ScalarOffset)):

tests/test_animation.py

@@ -1,6 +1,10 @@
 from time import perf_counter
 
+import pytest
+
 from textual.app import App, ComposeResult
+from textual.css.scalar import NULL_SCALAR, Scalar, ScalarOffset, Unit
+from textual.geometry import Offset
 from textual.reactive import var
 from textual.widgets import Static
 
@@ -39,6 +43,44 @@ async def test_animate_height() -> None:
         assert static.styles.height.value == 100
 
 
+destinations = [
+    ScalarOffset.from_offset((10, 5)),
+    Offset(10, 5),
+    (10, 5),
+    (10.0, 5.0),
+    "10 5",
+    "10.0 5.0",
+]
+
+
+@pytest.mark.parametrize("destination", destinations)
+async def test_animate_offset(destination) -> None:
+    """Test animating styles.offset works."""
+    # Styles.offset is a ScalarOffset, which makes it more complicated to animate
+
+    app = AnimApp()
+
+    async with app.run_test() as pilot:
+        static = app.query_one(Static)
+        assert static.offset == Offset(0, 0)
+        assert static.styles.offset == NULL_SCALAR
+
+        static.styles.animate("offset", destination, duration=0.5)
+        start = perf_counter()
+
+        # Wait for the animation to finished
+        await pilot.wait_for_animation()
+        elapsed = perf_counter() - start
+        # Check that the full time has elapsed
+        assert elapsed >= 0.5
+
+        # Check the offset reached the destination
+        assert static.styles.offset == ScalarOffset(
+            Scalar(10, Unit.CELLS, Unit.WIDTH),
+            Scalar(5, Unit.CELLS, Unit.HEIGHT),
+        )
+
+
 async def test_scheduling_animation() -> None:
     """Test that scheduling an animation works."""