added render measure

docs.md

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+# Documentation Workflow
+
+* Ensure you're inside a *Python 3.10+* virtual environment
+* Run the live-reload server using `mkdocs serve` from the project root
+* Create new pages by adding new directories and Markdown files inside `docs/*`
+
+## Commands
+
+- `mkdocs serve` - Start the live-reloading docs server.
+- `mkdocs build` - Build the documentation site.
+- `mkdocs -h` - Print help message and exit.
+
+## Project layout
+
+    mkdocs.yml    # The configuration file.
+    docs/
+        index.md  # The documentation homepage.
+        ...       # Other markdown pages, images and other files.

sandbox/will/scrolly.py

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+from rich.text import Text
+from textual.app import App, ComposeResult
+from textual.widgets import Static
+
+text = "\n".join("FOO BAR bazz etc sdfsdf " * 20 for n in range(1000))
+
+
+class Content(Static):
+    DEFAULT_CSS = """
+    Content {
+        width: auto;
+    }
+    """
+
+    def render(self):
+        return Text(text, no_wrap=False)
+
+
+class ScrollApp(App):
+    CSS = """
+    Screen {
+        overflow: auto;
+    }
+    """
+
+    def compose(self) -> ComposeResult:
+        yield Content()
+
+
+app = ScrollApp()
+if __name__ == "__main__":
+    app.run()

src/textual/render.py

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+from rich.console import Console, RenderableType
+
+
+def measure(console: Console, renderable: RenderableType, default: int) -> int:
+    """Measure a rich renderable.
+
+    Args:
+        console (Console): A console object.
+        renderable (RenderableType): Rich renderable.
+        default (int): Default width to use if renderable does not expose dimensions.
+
+    Returns:
+        int: Width in cells
+    """
+    get_console_width = getattr(renderable, "__rich_measure__", None)
+    if get_console_width is not None:
+        render_width = get_console_width(console, console.options).normalize().maximum
+        return max(0, render_width)
+    return default