Redraw only when something could have changed - save CPU usage

iboard.py

@@ -8,7 +8,7 @@ from pygame.event import Event
 
 class IBoard:
     @abstractmethod
-    def draw(self, screen: Surface):
+    def draw(self, screen: Surface, force_redraw: bool):
         raise NotImplementedError()
 
     @abstractmethod

menu.py

@@ -86,13 +86,16 @@ class MessageBoard(IBoard):
                                     (screen_rect.top + (screen_rect.height - text_rect.height)/2),
                                     text_rect.width, text_rect.height)
         self.bg_color = bg_color
+        self.was_drawn_already = False
 
     def handle_event(self, _):
         pass
 
-    def draw(self, screen: pygame.Surface):
-        screen.fill(self.bg_color)
-        self.font.render_to(screen, self.text_pos, self.text, fgcolor="black")
+    def draw(self, screen: pygame.Surface, force_redraw: bool):
+        if not self.was_drawn_already or force_redraw:
+            screen.fill(self.bg_color)
+            self.font.render_to(screen, self.text_pos, self.text, fgcolor="black")
+            self.was_drawn_already = True
 
 
 class MenuBoard(IBoard):
@@ -126,10 +129,11 @@ class MenuBoard(IBoard):
         for b in self.buttons:
             b.handle_event(event)
 
-    def draw(self, screen: pygame.Surface):
-        screen.fill(self.bg_color)
-        for b in self.buttons:
-            b.draw(screen)
+    def draw(self, screen: pygame.Surface, force_redraw: bool):
+        if force_redraw:
+            screen.fill(self.bg_color)
+            for b in self.buttons:
+                b.draw(screen)
 
 
 class App:
@@ -208,6 +212,7 @@ class App:
 
     def loop(self):
         self.running = True
+        needs_redrawing = True
         while self.running:
             try:
                 self.task_q.get_nowait()()
@@ -219,12 +224,14 @@ class App:
                 if self.screensaver_ticks != 0:
                     self.board.handle_event(event)
                 self.screensaver_ticks = self.TICKS_UNTIL_SCREENSAVER
+                needs_redrawing = True
 
             if self.screensaver_ticks == 0:
-                self.screensaver.draw(self.screen)
+                self.screensaver.draw(self.screen, False)
             else:
-                self.board.draw(self.screen)
+                self.board.draw(self.screen, needs_redrawing)
                 self.screensaver_ticks -= 1
+                needs_redrawing = False
 
             pygame.display.flip()
 

screensavers.py

@@ -20,7 +20,7 @@ class ClockScreensaver(Screensaver):
         self.dy = 1
         self.text_xy: Tuple[int, int] = (0, 0)
 
-    def draw(self, screen: pygame.Surface):
+    def draw(self, screen: pygame.Surface, _):
         text = strftime("%H:%M:%S")
         screen.fill("black")
         pygame.Rect(0, 0, screen.get_width(), screen.get_height())