simplify layout

notes/README.md

@@ -0,0 +1,3 @@
+# Developer notes
+
+These are notes made by the developer, and _not_ to be considered documentation.

notes/refresh.md

@@ -0,0 +1,11 @@
+# Refresh system
+
+This note describes how Textual updates widgets on-screen.
+
+if widget has made some changes and wishes to update visuals it can call Widget.refresh. There are two flags on this method; `repaint` which will repaint just the widget, and `layout` which will re-layout the screen. A layout must be done if the widget has changed size / position / visibility. Otherwise repaint will refresh just the widget area.
+
+A refresh won't happen immediately when `refresh()` is called, rather it sets internal flags. The `on_idle` method of Widget checks these flags. This is so that multiple changes made to the UI while processing events don't cause excessive repainting of the screen (which makes the UI slow and jumpy).
+
+In the case of a repaint. The Widget.on_idle handler will emit (send to the parent) an UpdateMessage. This message will be handled by the parent view, which will update the widget (a particular part of the screen).
+
+In the case of a layout. The Widget.on_idle handler will emit a LayoutMessage. This message will be handled by the parent view, which calls refresh_layout on the root view, which will layout and repaint the entire screen.

src/textual/geometry.py

@@ -74,6 +74,7 @@ class Size(NamedTuple):
     height: int
 
     def __bool__(self) -> bool:
+        """A Size is Falsey if it has area 0"""
         return self.width * self.height != 0
 
     @property
@@ -193,10 +194,12 @@ class Region(NamedTuple):
 
     @property
     def x_max(self) -> int:
+        """Maximum X value (non inclusive)"""
         return self.x + self.width
 
     @property
     def y_max(self) -> int:
+        """Maximum Y value (non inclusive)"""
         return self.y + self.height
 
     @property
@@ -226,10 +229,12 @@ class Region(NamedTuple):
 
     @property
     def x_range(self) -> range:
+        """A range object for X coordinates"""
         return range(self.x, self.x + self.width)
 
     @property
     def y_range(self) -> range:
+        """A range object for Y coordinates"""
         return range(self.y, self.y + self.height)
 
     def __add__(self, other: Any) -> Region:

src/textual/messages.py

@@ -13,10 +13,9 @@ if TYPE_CHECKING:
 
 @rich.repr.auto
 class UpdateMessage(Message, verbosity=3):
-    def __init__(self, sender: MessagePump, widget: Widget, layout: bool = False):
+    def __init__(self, sender: MessagePump, widget: Widget):
         super().__init__(sender)
         self.widget = widget
-        self.layout = layout
 
     def __rich_repr__(self) -> rich.repr.Result:
         yield self.sender
@@ -24,7 +23,7 @@ class UpdateMessage(Message, verbosity=3):
 
     def __eq__(self, other: object) -> bool:
         if isinstance(other, UpdateMessage):
-            return self.widget == other.widget and self.layout == other.layout
+            return self.widget == other.widget
         return NotImplemented
 
     def can_replace(self, message: Message) -> bool:

src/textual/view.py

@@ -94,15 +94,12 @@ class View(Widget):
         widget = message.widget
         assert isinstance(widget, Widget)
 
-        if message.layout:
-            await self.root_view.refresh_layout()
-            self.log("LAYOUT")
-
         display_update = self.root_view.layout.update_widget(self.console, widget)
         if display_update is not None:
             self.app.display(display_update)
 
     async def message_layout(self, message: LayoutMessage) -> None:
+        message.stop()
         await self.root_view.refresh_layout()
         self.app.refresh()
 

src/textual/widget.py

@@ -288,7 +288,7 @@ class Widget(MessagePump):
         elif self.check_repaint():
             self.render_cache = None
             self.reset_check_repaint()
-            await self.emit(UpdateMessage(self, self, layout=False))
+            await self.emit(UpdateMessage(self, self))
 
     async def focus(self) -> None:
         await self.app.set_focus(self)