checker example

docs/examples/guide/checker.py

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+from __future__ import annotations
+
+from textual.app import App, ComposeResult
+from textual.geometry import Size
+from textual.strip import Strip
+from textual.scroll_view import ScrollView
+
+from rich.segment import Segment
+
+
+class CheckerBoard(ScrollView):
+    COMPONENT_CLASSES = {
+        "checkerboard--white-square",
+        "checkerboard--black-square",
+        "checkerboard--void",
+    }
+
+    DEFAULT_CSS = """
+    CheckerBoard {
+        background: $primary;
+    }
+    CheckerBoard .checkerboard--void {
+        background: $background;
+    }
+
+    CheckerBoard .checkerboard--white-square {
+        background: $foreground 70%;
+    }
+    CheckerBoard .checkerboard--black-square {
+        background: $primary;
+    }
+    """
+
+    def on_mount(self) -> None:
+        self.virtual_size = Size(64, 32)
+
+    def render_line(self, y: int) -> Strip:
+        """Render a line of the widget. y is relative to the top of the widget."""
+
+        scroll_x, scroll_y = self.scroll_offset
+        y += scroll_y
+        row_index = y // 4  # four lines per row
+
+        white = self.get_component_rich_style("checkerboard--white-square")
+        black = self.get_component_rich_style("checkerboard--black-square")
+        void = self.get_component_rich_style("checkerboard--void")
+
+        if row_index >= 8:
+            return Strip.blank(self.size.width, void)
+
+        is_odd = row_index % 2
+
+        segments = [
+            Segment(" " * 8, black if (column + is_odd) % 2 else white)
+            for column in range(8)
+        ]
+        strip = Strip(segments, 8 * 8)
+        strip = strip.extend_cell_length(self.size.width, void)
+        strip = strip.crop(scroll_x, scroll_x + self.size.width)
+        return strip
+
+
+class BoardApp(App):
+    def compose(self) -> ComposeResult:
+        yield CheckerBoard()
+
+
+if __name__ == "__main__":
+    app = BoardApp()
+    app.run()