Pygame has a a few great interfaces that we can use to detect whether game character has overlapped each other or not and today we are going to look at one of them which is the pygame.sprite.collide_rect method. This method will take in two sprite objects that will then be used to find out the condition of the overlap. If no overlap happens then the above method will return False or else it will return True.
The script below is not perfect because it will only detect the overlapping once in the entire game and moves the enemy sprite in the opposite direction after the first overlapping occurs. This program is uses just to demonstrate to you how the above mentioned method works.
First thing we need to do before going into the main module is to modify the previous GameSprite module by making it a subclass of the pygame.sprite.Sprite class and then change it’s getImage method so we do not need to create a new GameSprite object on every loop pass just like before. Finally we will include a new detectCollide method which will return a boolean value indicates whether two sprite have overlapped each other or not.
import pygame from pygame.locals import * class GameSprite(pygame.sprite.Sprite): # Constructor. Pass in the image file # and it's width and height def __init__(self, image, width, height): # Call the parent class (Sprite) constructor pygame.sprite.Sprite.__init__(self) # Create the spritesheet surface from the image file self.sprite = pygame.image.load(image).convert_alpha() #register the width and height of the sprite self.width = width self.height = height def getImage(self, x_sprite, y_sprite, flip): # this method will return a subsurface which represents a portion of the spritesheet #the rectangle object uses in clipping self.clip_rect = Rect((x_sprite, y_sprite), (self.width, self.height)) self.sprite.set_clip(self.clip_rect) # clip a portion of the spritesheet with the rectangle object sub_surface = self.sprite.subsurface(self.sprite.get_clip()) #create sub surface return pygame.transform.flip(sub_surface, flip, False) #return a new flip surface def detectCollide(self, right, player_draw_pos, enemy_draw_pos): #return a boolean value indicates whether the player has collided with enemy or not # create the rectangle object for both enemy and player that will be used in the collide_rect function self.rect = Rect(player_draw_pos.x, player_draw_pos.y, self.width, self.height) right.rect = Rect(enemy_draw_pos.x, enemy_draw_pos.y, right.width, right.height) return pygame.sprite.collide_rect(self, right)
The next thing we need to do is to include the detectCollide method in our main game loop to detect the overlapping of two objects.
#!/usr/bin/env python import pygame from pygame.locals import * from sys import exit from vector2d import Vector2D from game_sprite import GameSprite robot_sprite_sheet = 'left.png' pygame.init() screen = pygame.display.set_mode((640, 480), 0, 32) #return a screen surface with desire screen size pygame.display.set_caption("Pygame Demo") w, h = 64, 64 # width and height of the sprite sprite_counter = 0 # initialize the sprite_counter game_frame = 0 # initialize the game_frame counter #direction control for player flip = False #direction control for enemy face_left = True clock = pygame.time.Clock() # initialize the clock object player_pos = Vector2D(30, 240) # initial position of the player sprite enemy_pos = Vector2D(450, 240) # initial position of the enemy sprite game_speed = 70. # speed per second #create the player sprite game_sprite = GameSprite(robot_sprite_sheet, w, h) #the enemy sprite object game_sprite_two = GameSprite(robot_sprite_sheet, w, h) while True: for event in pygame.event.get(): if event.type == QUIT: exit() v = Vector2D(0., 0.) # reset the speed to zero on each pass pressed_keys = pygame.key.get_pressed() # get all the keys from key-press events if pressed_keys[K_LEFT]: flip = True # if the user pressed the left arrow key then makes the sprite object facing left v = Vector2D(-1., 0.) # move the object one unit to the left elif pressed_keys[K_RIGHT]: flip = False # if the user pressed the right arrow key then makes the sprite object facing right v = Vector2D(1., 0.) # move the object one unit to the right screen.fill((205, 200, 215)) #blit the player with new position player_draw_pos = Vector2D(player_pos.x-w/2, player_pos.y-h/2) game_sprite_surface = game_sprite.getImage(sprite_counter * 64, 0, flip) # get the new sprite surface screen.blit(game_sprite_surface, player_draw_pos) #blit the enemy with new position enemy_draw_pos = Vector2D(enemy_pos.x-w/2, enemy_pos.y-h/2) game_sprite_surface_two = game_sprite_two.getImage(sprite_counter * 64, 0, face_left) # get the new sprite surface screen.blit(game_sprite_surface_two, enemy_draw_pos) #increase the sprite counter after x numbers of frame if(game_frame % 50 == 0): sprite_counter += 1 if(sprite_counter > 5): sprite_counter = 0 game_frame += 1 time_passed = clock.tick() #delta time for each frame time_passed_seconds = time_passed / 1000.0 #set the player's new position after each frame player_pos+= v * game_speed * time_passed_seconds #if player collides with enemy, enemy flips and changes it's direction if(game_sprite.detectCollide(game_sprite_two, player_draw_pos, enemy_draw_pos)): face_left = False if(face_left == True): enemy_pos += Vector2D(-1., 0.) * game_speed * time_passed_seconds else: enemy_pos += Vector2D(1., 0.) * game_speed * time_passed_seconds pygame.display.flip()
By running the above module you will see that after a contact has occurred the enemy sprite will move in the opposite direction.