The game loop is the heart of Serenity Valley, handling all game logic, event processing, and rendering in a continuous cycle.
Main Game Loop
The game loop is implemented in the run() method of the Game class (game.py:199-254):
def run(self):
print "Beginning run sequence."
# The main game loop
#
while True:
# Limit frame speed to 30 FPS
#
self.time_passed = self.clock.tick(30)
# If too long has passed between two frames, don't
# update (the game must have been suspended for some
# reason, and we don't want it to "jump forward"
# suddenly)
#
if self.time_passed > 100:
continue
active = False
for entry in self.textEntries:
if entry.clicked:
active = True
# Event loop
for event in pygame.event.get():
if event.type == pygame.QUIT:
self.quit()
elif event.type == pygame.KEYDOWN and not active:
if event.key == pygame.K_SPACE:
self.paused = not self.paused
elif event.key == pygame.K_g:
self.options['draw_grid'] = not self.options['draw_grid']
elif (event.type == pygame.MOUSEBUTTONDOWN and event.button == 1):
for button in self.buttons:
button.mouse_click_event(event.pos)
for entry in self.textEntries:
entry.mouse_click_event(event.pos)
# Update and draw
if not self.paused:
msg1 = ''
msg2 = ''
self.mboard_text = [msg1, msg2]
self.draw()
# Flip the display buffer
pygame.display.flip()
Frame Rate Control
The game uses pygame.time.Clock to maintain a consistent frame rate:
self.clock = pygame.time.Clock()
self.time_passed = self.clock.tick(30)
The tick() method automatically delays the loop to maintain 30 FPS, returning the milliseconds that passed since the last call.
Frame Skip Prevention
If more than 100ms passes between frames (indicating the game was suspended), the frame is skipped to prevent physics “jumping”:
if self.time_passed > 100:
continue
Event Handling
The game processes three main types of events:
1. Quit Events
if event.type == pygame.QUIT:
self.quit()
2. Keyboard Events
Keyboard events are only processed when text entries are not active:
elif event.type == pygame.KEYDOWN and not active:
if event.key == pygame.K_SPACE:
self.paused = not self.paused
elif event.key == pygame.K_g:
self.options['draw_grid'] = not self.options['draw_grid']
- Press SPACE to pause/unpause the game
- Press G to toggle the grid overlay
3. Mouse Events
Left mouse button clicks are dispatched to interactive widgets:
elif (event.type == pygame.MOUSEBUTTONDOWN and event.button == 1):
for button in self.buttons:
button.mouse_click_event(event.pos)
for entry in self.textEntries:
entry.mouse_click_event(event.pos)
Update and Draw Cycle
The game only updates and draws when not paused:
if not self.paused:
msg1 = ''
msg2 = ''
self.mboard_text = [msg1, msg2]
self.draw()
draw() method (game.py:186-197) handles all rendering:
def draw(self):
# Draw background image
self.draw_background()
# Decide if we should draw grid
if self.options['draw_grid']:
self.draw_grid()
self.tboard.draw()
for obj in self.world:
obj.draw()
All drawing happens to an off-screen buffer. The final pygame.display.flip() swaps the buffers to display the rendered frame.
Pause Functionality
The pause system is controlled by a boolean flag:
self.paused = False # Initialized in __init__ (game.py:122)
- Events are still processed (allowing unpause)
- Game logic and rendering are skipped
- The display continues to show the last rendered frame
The pause mechanism is simple but effective - it completely halts game updates while keeping the event system responsive.
Game Loop Flow
The loop continues indefinitely until a QUIT event is received, at which point sys.exit() is called.