Cascading windows

changes/2023.feature.rst

@@ -0,0 +1 @@
+The initial position of each newly created window is now different, cascading down the screen as windows are created.

cocoa/src/toga_cocoa/window.py

@@ -2,6 +2,7 @@
 
 from toga.command import Command, Separator
 from toga.types import Position, Size
+from toga.window import _initial_position
 from toga_cocoa.container import Container
 from toga_cocoa.libs import (
     SEL,
@@ -161,7 +162,7 @@ def __init__(self, interface, title, position, size):
 
         self.set_title(title)
         self.set_size(size)
-        self.set_position(position)
+        self.set_position(position if position is not None else _initial_position())
 
         self.native.delegate = self.native
 

core/src/toga/app.py

@@ -193,7 +193,7 @@ def __init__(
         self,
         id: str | None = None,
         title: str | None = None,
-        position: PositionT = Position(100, 100),
+        position: PositionT | None = None,
         size: SizeT = Size(640, 480),
         resizable: bool = True,
         minimizable: bool = True,

core/src/toga/window.py

@@ -27,6 +27,29 @@
     from toga.widgets.base import Widget
 
 
+_window_count = -1
+
+
+def _initial_position() -> Position:
+    """Compute a cascading initial position for platforms that don't have a native
+    implementation.
+
+    This is a stateful method; each time it is invoked, it will yield a new initial
+    position.
+
+    :returns: The position for the new window.
+    """
+    # Each new window created without an explicit position is positioned
+    # 50px down and to the right from the previous window, with the first
+    # window positioned at (100, 100). Every 15 windows, move back to a
+    # y coordinate of 100, and start from 50 pixels further right.
+    global _window_count
+    _window_count += 1
+
+    pos = 100 + (_window_count % 15) * 50
+    return Position(pos + (_window_count // 15 * 50), pos)
+
+
 class FilteredWidgetRegistry:
     # A class that exposes a mapping lookup interface, filtered to widgets from a single
     # window. The underlying data store is on the app.
@@ -117,7 +140,7 @@ def __init__(
         self,
         id: str | None = None,
         title: str | None = None,
-        position: PositionT = Position(100, 100),
+        position: PositionT | None = None,
         size: SizeT = Size(640, 480),
         resizable: bool = True,
         closable: bool = True,
@@ -178,13 +201,11 @@ def __init__(
         self._minimizable = minimizable
 
         self.factory = get_platform_factory()
-        position = Position(*position)
-        size = Size(*size)
         self._impl = getattr(self.factory, self._WINDOW_CLASS)(
             interface=self,
             title=title if title else self._default_title,
-            position=position,
-            size=size,
+            position=None if position is None else Position(*position),
+            size=Size(*size),
         )
 
         # Add the window to the app

core/tests/app/test_mainwindow.py

@@ -20,7 +20,8 @@ def test_create(app):
     assert isinstance(window.id, str)
     # Window title is the app title.
     assert window.title == "Test App"
-    assert window.position == (100, 100)
+    # The app has created a main window, so this will be the second window.
+    assert window.position == (150, 150)
     assert window.size == (640, 480)
     assert window.resizable
     assert window.closable

core/tests/conftest.py

@@ -3,12 +3,16 @@
 import pytest
 
 import toga
+from toga import window as toga_window
 from toga_dummy.utils import EventLog
 
 
 @pytest.fixture(autouse=True)
-def reset_event_log():
+def reset_global_state():
+    # Clear the testing event log
     EventLog.reset()
+    # Reset the global window count
+    toga_window._window_count = -1
 
 
 @pytest.fixture(autouse=True)

core/tests/window/test_window.py

@@ -29,7 +29,8 @@ def test_window_created(app):
     # We can't know what the ID is, but it must be a string.
     assert isinstance(window.id, str)
     assert window.title == "Toga"
-    assert window.position == toga.Position(100, 100)
+    # The app has created a main window, so this will be the second window.
+    assert window.position == toga.Position(150, 150)
     assert window.size == toga.Size(640, 480)
     assert window.resizable
     assert window.closable
@@ -207,6 +208,48 @@ def test_set_position(window):
     assert window.position == toga.Position(123, 456)
 
 
+def test_position_cascade(app):
+    """The initial position of windows will cascade."""
+    windows = [app.main_window]
+
+    for i in range(0, 14):
+        win = toga.Window(title=f"Window {i}")
+        # The for the first 14 new windows (the app creates the first window)
+        # the x and y coordinates must be the same
+        assert win.position[0] == win.position[1]
+        # The position of the window should cascade down
+        assert win.position[0] > windows[-1].position[0]
+        assert win.position[1] > windows[-1].position[1]
+
+        windows.append(win)
+
+    # The 15th window will come back to the y origin, but shift along the x axis.
+    win = toga.Window(title=f"Window {i}")
+    assert win.position[0] > windows[0].position[0]
+    assert win.position[1] == windows[0].position[1]
+
+    windows.append(win)
+
+    # Cascade another 15 windows
+    for i in range(16, 30):
+        win = toga.Window(title=f"Window {i}")
+        # The position of the window should cascade down
+        assert win.position[0] > windows[-1].position[0]
+        assert win.position[1] > windows[-1].position[1]
+
+        # The y coordinate of these windows should be the same
+        # as 15 windows ago; the x coordinate is shifted right
+        assert win.position[0] > windows[i - 15].position[0]
+        assert win.position[1] == windows[i - 15].position[1]
+
+        windows.append(win)
+
+    # The 30 window will come back to the y origin, but shift along the x axis.
+    win = toga.Window(title=f"Window {i}")
+    assert win.position[0] > windows[15].position[0]
+    assert win.position[1] == windows[15].position[1]
+
+
 def test_set_size(window):
     """The size of the window can be set."""
     window.size = (123, 456)
@@ -392,9 +435,11 @@ def test_screen(window, app):
     # window between the screens.
     # `window.screen` will return `Secondary Screen`
     assert window.screen == app.screens[1]
-    assert window.position == toga.Position(100, 100)
+    # The app has created a main window; the secondary window will be at second
+    # position.
+    assert window.position == toga.Position(150, 150)
     window.screen = app.screens[0]
-    assert window.position == toga.Position(1466, 868)
+    assert window.position == toga.Position(1516, 918)
 
 
 def test_screen_position(window, app):

dummy/src/toga_dummy/window.py

@@ -2,6 +2,7 @@
 
 import toga_dummy
 from toga.types import Size
+from toga.window import _initial_position
 
 from .screens import Screen as ScreenImpl
 from .utils import LoggedObject
@@ -50,7 +51,7 @@ def __init__(self, interface, title, position, size):
         self.container = Container()
 
         self.set_title(title)
-        self.set_position(position)
+        self.set_position(position if position is not None else _initial_position())
         self.set_size(size)
 
     def create_toolbar(self):

gtk/src/toga_gtk/window.py

@@ -4,6 +4,7 @@
 
 from toga.command import Separator
 from toga.types import Position, Size
+from toga.window import _initial_position
 
 from .container import TogaContainer
 from .libs import Gdk, Gtk
@@ -30,7 +31,7 @@ def __init__(self, interface, title, position, size):
         self.native.set_default_size(size[0], size[1])
 
         self.set_title(title)
-        self.set_position(position)
+        self.set_position(position if position is not None else _initial_position())
 
         # Set the window deletable/closable.
         self.native.set_deletable(self.interface.closable)

testbed/tests/app/test_app.py

@@ -6,7 +6,7 @@
 from toga.colors import CORNFLOWERBLUE, FIREBRICK, REBECCAPURPLE
 from toga.style.pack import Pack
 
-from ..test_window import window_probe
+from ..window.test_window import window_probe
 
 
 @pytest.fixture