Space shooting lesson 08: improved collision

Space shooting No 08 course ： Improved collision

This is us. “Shmup” Project No 5 part . If you haven't read through the previous section , Please from The first 1 part Start . In this lesson , We will discuss how to change Pygame The way to deal with conflicts between elves .

What happened to the collision ？

In the last tutorial , We added graphics , Change the sprite from a normal rectangle to a more beautiful PNG Images . However , This brings up a problem ： Sometimes the game will think that there is a collision between the player and the meteor , And it seems that they didn't hit at all . To understand what happened , Let's see a picture ：

Pygame The default conflict type in is to use collide_rect() function , This function uses two sprites rect Property to calculate whether they overlap . This is known as AABB Collision , It's very fast and reliable . however , If the sprite image is not rectangular , Then you will encounter rectangle overlap similar to that in the picture . At this time collide_rect() The return value of the function is True, Players will feel frustrated , Because they think they should have successfully avoided the meteor .

If you are in this situation , There are several ways to try ：

By using collide_rect_ratio() function , You can use smaller rectangles , Thus reducing the amount of space that can be counted as overlap . According to the shape of the spirit , It works well . Notice how the tip of the wing is outside the rectangle . This means that in some cases the star seems to pass through the wing , It will not count as an impact . This is actually a good situation ！ At the speed of things moving in the game , Players will not notice this directly , And I just think they “ get away ” A very close dodge . They don't feel depressed , Instead, I will feel that I have done well .

Another option is to use a circular bounding box . For meteors , This is a very good choice . It is not suitable for this ship , But the same , It's not a bad thing that the wing is outside the collision .

Set the radius of the sprite

According to the above options , We will choose a circle for the collision between meteors and players .Pygame Make it easy - We just need to set a new attribute on each wizard ：self.radius.

Let's start with players . How big should the collision ring be ？ It may take a little experiment to get the correct value . The following is how to perform this operation in the player wizard ：__init()__

	self.rect = self.image.get_rect()
	self.radius = 25
	pygame.draw.circle(self.image, RED, self.rect.center, self.radius)

We draw a red circle at the top of the player image , So that we can see its appearance . Let's do the same thing with meteors ：

	self.rect = self.image.get_rect()
	self.radius = int(self.rect.width / 2)
	pygame.draw.circle(self.image, RED, self.rect.center, self.radius)

under these circumstances , We are planning ahead . We may decide to use meteor images of different sizes . By setting the radius to 1⁄2, We can do that , Without having to adjust the code later .

Here is our final result ：

You can see , For player elves , Our radius may be too large —— It's actually y The axis is larger than the size of the spacecraft . To get closer to the above example , Let's set up players self.radius = 20.

For meteors , We want to highlight a little bit , So let's scale the circle to the size 85%：

	self.radius = int(self.rect.width * .85 / 2)

Change the collision type

Let the game start using these circles for collision testing , We just need to change spritecollide Command to use the circle function instead of AABB function ：

	# check to see if a mob hit the player
    hits = pygame.sprite.spritecollide(player, mobs, False, pygame.sprite.collide_circle)
    if hits:
        running = False

Once you try , And you are satisfied with the way the collision works , You can delete the red circle . I suggest you just comment out the command , Instead of deleting them , In case you want to use them again in the future .

Conclusion

Determining the right collision style can greatly change the feel of the game . We now have a better meteor collision with players , But please pay attention to , We haven't changed the style of bullets colliding with meteors . Circle is a bad choice for the shape of bullets , So it's best to keep them rectangular .

thereinafter , We will make things lively by learning how to add animation to sprites

The complete code of this part

# KidsCanCode - Game Development with Pygame video series
# Shmup game - part 5
# Video link: https://www.youtube.com/watch?v=_y5U8tB36Vk
# Improved collisions
import pygame
import random
from os import path

img_dir = path.join(path.dirname(__file__), 'img')

WIDTH = 480
HEIGHT = 600
FPS = 60

# define colors
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)
YELLOW = (255, 255, 0)

# initialize pygame and create window
pygame.init()
pygame.mixer.init()
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Shmup!")
clock = pygame.time.Clock()

class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.transform.scale(player_img, (50, 38))
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        self.radius = 20
        # pygame.draw.circle(self.image, RED, self.rect.center, self.radius)
        self.rect.centerx = WIDTH / 2
        self.rect.bottom = HEIGHT - 10
        self.speedx = 0

    def update(self):
        self.speedx = 0
        keystate = pygame.key.get_pressed()
        if keystate[pygame.K_LEFT]:
            self.speedx = -8
        if keystate[pygame.K_RIGHT]:
            self.speedx = 8
        self.rect.x += self.speedx
        if self.rect.right > WIDTH:
            self.rect.right = WIDTH
        if self.rect.left < 0:
            self.rect.left = 0

    def shoot(self):
        bullet = Bullet(self.rect.centerx, self.rect.top)
        all_sprites.add(bullet)
        bullets.add(bullet)

class Mob(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = meteor_img
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        self.radius = int(self.rect.width * .85 / 2)
        # pygame.draw.circle(self.image, RED, self.rect.center, self.radius)
        self.rect.x = random.randrange(WIDTH - self.rect.width)
        self.rect.y = random.randrange(-100, -40)
        self.speedy = random.randrange(1, 8)
        self.speedx = random.randrange(-3, 3)

    def update(self):
        self.rect.x += self.speedx
        self.rect.y += self.speedy
        if self.rect.top > HEIGHT + 10 or self.rect.left < -25 or self.rect.right > WIDTH + 20:
            self.rect.x = random.randrange(WIDTH - self.rect.width)
            self.rect.y = random.randrange(-100, -40)
            self.speedy = random.randrange(1, 8)

class Bullet(pygame.sprite.Sprite):
    def __init__(self, x, y):
        pygame.sprite.Sprite.__init__(self)
        self.image = bullet_img
        self.image.set_colorkey(BLACK)
        self.rect = self.image.get_rect()
        self.rect.bottom = y
        self.rect.centerx = x
        self.speedy = -10

    def update(self):
        self.rect.y += self.speedy
        # kill if it moves off the top of the screen
        if self.rect.bottom < 0:
            self.kill()

# Load all game graphics
background = pygame.image.load(path.join(img_dir, "starfield.png")).convert()
background_rect = background.get_rect()
player_img = pygame.image.load(path.join(img_dir, "playerShip1_orange.png")).convert()
meteor_img = pygame.image.load(path.join(img_dir, "meteorBrown_med1.png")).convert()
bullet_img = pygame.image.load(path.join(img_dir, "laserRed16.png")).convert()

all_sprites = pygame.sprite.Group()
mobs = pygame.sprite.Group()
bullets = pygame.sprite.Group()
player = Player()
all_sprites.add(player)
for i in range(8):
    m = Mob()
    all_sprites.add(m)
    mobs.add(m)

# Game loop
running = True
while running:
    # keep loop running at the right speed
    clock.tick(FPS)
    # Process input (events)
    for event in pygame.event.get():
        # check for closing window
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_SPACE:
                player.shoot()

    # Update
    all_sprites.update()

    # check to see if a bullet hit a mob
    hits = pygame.sprite.groupcollide(mobs, bullets, True, True)
    for hit in hits:
        m = Mob()
        all_sprites.add(m)
        mobs.add(m)

    # check to see if a mob hit the player
    hits = pygame.sprite.spritecollide(player, mobs, False, pygame.sprite.collide_circle)
    if hits:
        running = False

    # Draw / render
    screen.fill(BLACK)
    screen.blit(background, background_rect)
    all_sprites.draw(screen)
    # *after* drawing everything, flip the display
    pygame.display.flip()

pygame.quit()

The first 6 part ： Sprite animation