Simple pygame foundation for transition between different views (for a typical game)

pygame-transitions.py

import pygame
import sys
from pygame.locals import *

BACKGROUND_COLOR = pygame.Color(0, 0, 100)
TEXT_COLOR = pygame.Color(255, 255, 255)
SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600
HALF_SCREEN_WIDTH = SCREEN_WIDTH / 2
HALF_SCREEN_HEIGHT = SCREEN_HEIGHT / 2

VIEW_STATE_SPLASH = 0
VIEW_STATE_MENU = 1
VIEW_STATE_GAME_A = 2
VIEW_STATE_GAME_B = 3
VIEW_STATE_OPTIONS = 4
VIEW_STATE_QUITTING = 5
VIEW_STATE_QUIT = 6


###### BASE CLASS FOR VIEWS
class View:
	def __init__(self, screen):
		self.screen = screen

	# called when transitioning to this view
	def prepare(self):
		pass

	# handle events for this view
	def handleEvents(self):
		for event in pygame.event.get():
			pass

	# render this view
	def render(self):
		self.screen.fill(BACKGROUND_COLOR)

	# returns a view id if the game should transition to another view, None else
	def transition(self):
		return None

	def __str__(self):
		return type(self).__name__


class TextView(View):
	# Displays a text on screen
	# 
	# Shows text for 2 seconds then proceed to next view
	firstRender = True
	startTime = 0

	def __init__(self, screen, text, nextView):
		View.__init__(self, screen)
		self.text = text
		self.font = pygame.font.SysFont("comicsansmsttf", 40)
		self.textSurface = self.font.render(self.text, True, TEXT_COLOR)
		self.nextView = nextView

	def prepare(self):
		self.startTime = pygame.time.get_ticks()
			
	def render(self):
		textSize = self.font.size(self.text)
		textX = HALF_SCREEN_WIDTH - (textSize[0] / 2)
		textY = HALF_SCREEN_HEIGHT  - (textSize[1] / 2)

		self.screen.fill(BACKGROUND_COLOR)
		self.screen.blit(self.textSurface, [textX, textY])
	
	def transition(self):
		nextView = None
		if pygame.time.get_ticks() - self.startTime >= 2000:
			nextView = self.nextView
		return nextView

	def __str__(self):
		return "%s(\"%s\")" % (type(self).__name__, self.text)



class MenuView(View):
	# Displays the main menu

	titleText = "Game title"
	menuItems = ['Game A', 'Game B', 'Options', 'Quit']
	selectedItem = 0
	centerX = HALF_SCREEN_WIDTH
	centerY = HALF_SCREEN_HEIGHT
	
	MENU_ITEM_GAME_A = 0
	MENU_ITEM_GAME_B = 1
	MENU_ITEM_OPTIONS = 2
	MENU_ITEM_QUIT = 3

	MENU_ITEM_TO_VIEW_STATE = {
		MENU_ITEM_GAME_A: VIEW_STATE_GAME_A,
		MENU_ITEM_GAME_B: VIEW_STATE_GAME_B,
		MENU_ITEM_OPTIONS: VIEW_STATE_OPTIONS,
		MENU_ITEM_QUIT: VIEW_STATE_QUITTING,
	}

	def __init__(self, screen):
		View.__init__(self, screen)

	def prepare(self):
		self.transitionToState = None

	def handleEvents(self):
		for event in pygame.event.get():
			if event.type == pygame.QUIT:
				done = True
			if event.type == pygame.KEYDOWN:
				if event.key == K_DOWN:
					self.selectedItem = (self.selectedItem + 1) % len(self.menuItems)
				if event.key == K_UP:
					self.selectedItem = (self.selectedItem - 1) % len(self.menuItems)
				if event.key == K_RETURN:
					# print("clicked menu item '%s'" % self.menuItems[self.selectedItem])
					self.transitionToState = self.MENU_ITEM_TO_VIEW_STATE[self.selectedItem]

	def renderMenuItems(self, screen, selectedItem):	
		index = 0
		for menuItemText in self.menuItems:
			textX = self.centerX - 100
			textY = self.centerY - 50 + (40 * index)
			if self.selectedItem == index:
				textSurface = menuSelectedFont.render(menuItemText, True, TEXT_COLOR)
				pygame.draw.circle(self.screen, TEXT_COLOR, (textX - 15, textY + 15), 5)
			else:
				textSurface = menuFont.render(menuItemText, True, TEXT_COLOR)
			self.screen.blit(textSurface, [textX, textY])
			index += 1


	def render(self):
		textSurface = titleFont.render(self.titleText, True, TEXT_COLOR)
		self.screen.fill(BACKGROUND_COLOR)
		self.screen.blit(textSurface, [HALF_SCREEN_WIDTH - 150, HALF_SCREEN_HEIGHT - 150])
		self.renderMenuItems(self.screen, self.selectedItem)

	def transition(self):
		return self.transitionToState


class QuitView(View):
	# Dummy screen that just quits the game (after quitting screen has been shown)
	def __init__(self, screen):
		View.__init__(self, screen)

	def prepare(self):
		sys.exit()


######################### START OF PROGRAM

pygame.init()

titleFont = pygame.font.SysFont("comicsansmsttf", 60)
menuFont = pygame.font.SysFont("comicsansmsttf", 30)
menuSelectedFont = pygame.font.SysFont("comicsansmsttf", 30, True)

screen = pygame.display.set_mode([SCREEN_WIDTH, SCREEN_HEIGHT])


views = {\
	VIEW_STATE_SPLASH: 		TextView(screen, "Nonexistant games presents", VIEW_STATE_MENU),
	VIEW_STATE_MENU: 		MenuView(screen),
	VIEW_STATE_GAME_A: 		TextView(screen, "Game A screen...", VIEW_STATE_MENU),
	VIEW_STATE_GAME_B: 		TextView(screen, "Game B screen...", VIEW_STATE_MENU),
	VIEW_STATE_OPTIONS: 	TextView(screen, "Game options screen", VIEW_STATE_MENU),
	VIEW_STATE_QUITTING: 	TextView(screen, "Bye bye!", VIEW_STATE_QUIT),
	VIEW_STATE_QUIT: 		QuitView(screen)
}


currentViewId = VIEW_STATE_SPLASH
currentViewState = views[currentViewId]
currentViewState.prepare()

print("Showing %s" % currentViewState)

while True:

	currentViewState.handleEvents()
	currentViewState.render();

	pygame.display.flip()
	pygame.time.delay(100)

	nextViewId = currentViewState.transition()
	if nextViewId:
		print("Transition from %s -> %s" % (currentViewState, views[nextViewId]))
		currentViewId = nextViewId
		currentViewState = views[currentViewId]
		currentViewState.prepare()