Stream layout

Author: willmcgugan

.gitignore

@@ -29,6 +29,7 @@ lib/
 lib64/
 parts/
 sdist/
+dist/
 var/
 wheels/
 *.egg-info/

src/textual/css/constants.py

@@ -28,7 +28,7 @@
     "wide",
 }
 VALID_EDGE: Final = {"top", "right", "bottom", "left", "none"}
-VALID_LAYOUT: Final = {"vertical", "horizontal", "grid"}
+VALID_LAYOUT: Final = {"vertical", "horizontal", "grid", "stream"}
 
 VALID_BOX_SIZING: Final = {"border-box", "content-box"}
 VALID_OVERFLOW: Final = {"scroll", "hidden", "auto"}

src/textual/css/styles.py

@@ -284,7 +284,7 @@ class StylesBase:
     layout = LayoutProperty()
     """Set the layout of the widget, defining how it's children are laid out.
     
-    Valid values are "grid", "horizontal", and "vertical" or None to clear any layout
+    Valid values are "grid", "stream", "horizontal", or "vertical" or None to clear any layout
     that was set at runtime.
 
     Raises:

src/textual/layouts/factory.py

@@ -3,12 +3,14 @@
 from textual.layout import Layout
 from textual.layouts.grid import GridLayout
 from textual.layouts.horizontal import HorizontalLayout
+from textual.layouts.stream import StreamLayout
 from textual.layouts.vertical import VerticalLayout
 
 LAYOUT_MAP: dict[str, type[Layout]] = {
     "horizontal": HorizontalLayout,
     "grid": GridLayout,
     "vertical": VerticalLayout,
+    "stream": StreamLayout,
 }
 
 

src/textual/layouts/stream.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from textual.geometry import NULL_OFFSET, Region, Size
+from textual.layout import ArrangeResult, Layout, WidgetPlacement
+
+if TYPE_CHECKING:
+
+    from textual.widget import Widget
+
+
+class StreamLayout(Layout):
+    name = "stream"
+
+    def arrange(
+        self, parent: Widget, children: list[Widget], size: Size, greedy: bool = True
+    ) -> ArrangeResult:
+        parent.pre_layout(self)
+        viewport = parent.app.size
+
+        placements: list[WidgetPlacement] = []
+        if not children:
+            return []
+        width = size.width
+        first_child_styles = children[0].styles
+        y = first_child_styles.margin.top
+        previous_margin = 0
+        null_offset = NULL_OFFSET
+
+        for widget in children:
+            styles = widget.styles
+            overlay = styles.overlay == "screen"
+            absolute = styles.has_rule("position") and styles.position == "absolute"
+            margin = styles.margin
+            top, right, bottom, left = margin
+            margin_width = left + right
+            y += max(top, previous_margin)
+            previous_margin = bottom
+            height = widget.get_content_height(size, viewport, width - margin_width)
+            height += styles.gutter.height
+            if (max_height := styles.max_height) is not None and max_height.is_cells:
+                height = min(height, int(max_height.value))
+            placements.append(
+                WidgetPlacement(
+                    Region(left, y, width - margin_width, height),
+                    null_offset,
+                    margin,
+                    widget,
+                    0,
+                    False,
+                    overlay,
+                    absolute,
+                )
+            )
+            y += height
+
+        return placements