core: simplify homescreen and lockscreen implementations

core/src/apps/homescreen/__init__.py

@@ -1,11 +1,10 @@
 import storage.device
-from trezor import io, res, ui
+from trezor import loop, res, ui
-
-if False:
-    from typing import Any, Coroutine
 
 
 class HomescreenBase(ui.Layout):
+    RENDER_SLEEP = loop.SLEEP_FOREVER
+
     def __init__(self) -> None:
         self.repaint = True
 
@@ -17,16 +16,3 @@ class HomescreenBase(ui.Layout):
     def render_homescreen(self) -> None:
         ui.display.avatar(48, 48 - 10, self.image, ui.WHITE, ui.BLACK)
         ui.display.text_center(ui.WIDTH // 2, 220, self.label, ui.BOLD, ui.FG, ui.BG)
-
-    def dispatch(self, event: int, x: int, y: int) -> None:
-        if event is ui.RENDER and self.repaint:
-            self.repaint = False
-            self.on_render()
-        elif event is io.TOUCH_END:
-            self.on_touch_end(x, y)
-
-    def __iter__(self) -> Coroutine[Any, Any, ui.ResultValue]:
-        # called whenever `await homescreen` is invoked.
-        # we want to repaint once after that and then never again
-        self.repaint = True
-        return super().__iter__()

core/src/apps/homescreen/lockscreen.py

@@ -1,4 +1,4 @@
-from trezor import loop, res, ui, wire
+from trezor import res, ui, wire
 
 from . import HomescreenBase
 
@@ -20,6 +20,8 @@ async def lockscreen() -> None:
 
 
 class Lockscreen(HomescreenBase):
+    BACKLIGHT_LEVEL = ui.BACKLIGHT_LOW
+
     def __init__(
         self, lock_label: str = "Locked", tap_label: str = "Tap to unlock"
     ) -> None:
@@ -39,33 +41,6 @@ class Lockscreen(HomescreenBase):
         )
         ui.display.icon(45, 202, res.load(ui.ICON_CLICK), ui.TITLE_GREY, ui.BG)
 
-    def handle_rendering(self) -> loop.Task:  # type: ignore
-        """Task that is rendering the layout in a busy loop.
-
-        Copy-pasted from ui.Layout.handle_rendering with modification to set the
-        backlight to a lower level while lockscreen is on, and a longer sleep because
-        we never do any redrawing."""
-        # Before the first render, we dim the display.
-        ui.backlight_fade(ui.BACKLIGHT_DIM)
-        # Clear the screen of any leftovers, make sure everything is marked for
-        # repaint (we can be running the same layout instance multiple times)
-        # and paint it.
-        ui.display.clear()
-        self.on_render()
-
-        if __debug__ and self.should_notify_layout_change:
-            from apps.debug import notify_layout_change
-
-            self.should_notify_layout_change = False
-            notify_layout_change(self)
-
-        ui.refresh()
-        ui.backlight_fade(ui.BACKLIGHT_LOW)
-        # long sleep
-        sleep = loop.sleep(1000 * 1000 * 1000)
-        while True:
-            yield sleep
-
     def on_render(self) -> None:
         self.render_homescreen()
         self.render_lock()

core/src/trezor/loop.py

@@ -222,6 +222,10 @@ class Syscall:
         pass
 
 
+SLEEP_FOREVER = Syscall()
+"""Tasks awaiting `SLEEP_FOREVER` will never be resumed."""
+
+
 class sleep(Syscall):
     """
     Pause current task and resume it after given delay.  Although the delay is

core/src/trezor/ui/__init__.py

@@ -305,6 +305,9 @@ class Layout(Component):
     raised, usually from some of the child components.
     """
 
+    BACKLIGHT_LEVEL = style.BACKLIGHT_NORMAL
+    RENDER_SLEEP = loop.sleep(_RENDER_DELAY_US)  # type: loop.Syscall
+
     async def __iter__(self) -> ResultValue:
         """
         Run the layout and wait until it completes.  Returns the result value.
@@ -381,8 +384,8 @@ class Layout(Component):
         # rendering everything synchronously, so refresh it manually and turn
         # the brightness on again.
         refresh()
-        backlight_fade(style.BACKLIGHT_NORMAL)
+        backlight_fade(self.BACKLIGHT_LEVEL)
-        sleep = loop.sleep(_RENDER_DELAY_US)
+        sleep = self.RENDER_SLEEP
         while True:
             # Wait for a couple of ms and render the layout again.  Because
             # components use re-paint marking, they do not really draw on the