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Finished Chapter 12

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Jason Zhu 2020-09-10 21:02:06 +10:00
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# Chapter 12. A Ship that Fires Bullets
## Starting the Game Project
```python
import sys
import pygame
class AlienInvasion:
"""Overall class to manage game assets and behaviour"""
def __init__(self):
"""Initialize the game, and create game resources."""
pygame.init()
self.screen = pygame.display.set_mode((1200, 800))
pygame.display.set_caption("Alien Invasion")
def run_game(self):
"""Start the main loop for the game"""
while True:
# event loop, watch for mouse/keyboard events
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
# Make the most recently draw screen visible
pygame.display.flip()
if __name__ == '__main__':
ai = AlienInvasion()
ai.run_game()
```
* `pygame.display.set_mode()` assigned a **surface** to `self.screen`, which is a part of the screen where a game element can be displayed.
* When we activate the game's animation loop, this surface will be redrawn every time.
* Game is contolled by `run_game()` method. containing
* event loop block
* code that manages screen updates.
* To access the events that Pygame detects, use `pygame.event.get()` function. In each loop, any keyboard/mouse event will cause the `for` loop to run.
### Creating a Settings Class
In order to manage the setting more efficiently, we move setting into a separate module `settings.py`
```python
class Settings:
"""A class to store all settings for Alien Invasion"""
def __init__(self):
"""Initialize the game's settings."""
# Screen settings
self.screen_width = 1200
self.screen_height = 800
self.bg_color = (230,230,230)
```
`alien_invasion.py` will also be modified to fit it.
## Adding The Ship Image
* Verify it's free licensed image
### Creating the Ship Class
Create this `ship.py` module
```python
import pygame
class Ship:
"""A class to manage the ship."""
def __init__(self, ai_game):
"""Initialize the ship and set its starting position"""
self.screen = ai_game.screen
self.screen_rect = ai_game.screen.get_rect()
# Load the ship image and get its rect
self.image = pygame.image.load('ship.bmp')
self.rect = self.image.get_rect()
# Start each new ship at the bottom center of the screen
self.rect.midbottom = self.screen_rect.midbottom
def blitme(self):
"""Draw the ship at its current location"""
self.screen.blit(self.image,self.rect)
```
* Pygame treat all game elements like rectangles (rects). So, collision of objects can be calculated via `get_rect()` method
* `pygame.image.load()` is called to load the image
* When the image is loaded, we call `get_rect()` to access ship surface's `rect` attribute
How to work with a `rect` object:
* Use x,y coord of top, bottom, left and right edges of the rect.
* We can set any of these values to establish the current position of the rect.
* When working center of a game element, use `center`, `centerx`, or `centery` attribute of a rect.
* When working with edge of the screen: work with `top`, `bottom`, `left` or `right` attributes.
* When adjust horizontal/vertical placement of rect, just use `x` & `y` attributes.
* `(0,0)` is the top-left corner of the screen.
### Drawing the Ship to the Screen
Modify `alien_invasion.py` by:
1. Add ship object in `__init__`
2. Add `self.ship.blitme()` in screen redraw code block
## Refactoring: The _check_events() and _update_screen() methods
Refactor code:
* simplifies the structure
* Make it easier to build on.
Here we refactor the code by break the `run_game()`:
* Move code for managing events to `_check_events()`
* Move code for updating the screen to `_update_screen()`
**helper method**:
* is a method in class but isn't meant to be called through an instance.
* syntax: a single leading underscore
### `_check_events()` Method
Create function in `AlienInvasion` and replace original code snippet in while loop
```python
def _check_events(self):
"""Respond to keypresses and mouse events."""
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
```
### `_update_screen()` Method
Create function `_update_screen()` and replace original code snippet
```python
def _update_screen(self):
"""Update images on the screen, and flip to the new screen"""
self.screen.fill(self.settings.bg_color)
self.ship.blitme()
```
```python
def run_game(self):
"""Start the main loop for the game"""
while True:
self._check_events()
self._update_screen()
```
After replacing lengthy codes with helper function, `run_game` now become simpler. This is a way of refactoring the code
## Piloting the Ship
Now write code that responds when player presses the right or left arrow key.
### Responding to a Keypress
* Whenever the player presses a key, the keypress is registered in Pygame as an event.
* Each event is picked by `pygame.event.get()` method.
* We can specify in `_check_events()` method what kind of events we want the game to check for.
* Each keypress is registered as a `KEYDOWN` event
* If a `K_RIGHT` event is found, move the ship to right by increasing the value `self.ship.rect.x` by 1
```python
def _check_events(self):
"""Respond to keypresses and mouse events."""
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
elif event.type == pygame.KEYDOWN:
if event.key == pygame.K_RIGHT:
self.ship.rect.x += 1
```
### Allowing Continuous Movement
* We can detect whether the key is released using `KEYUP` event.
* We can use `KEYDOWN` & `KEYUP` events together with a flag called `moving_right` to implement continuous motion
* When `moving_right` flag is `False`, the ship will be motionless.
* Create an attribute called `moving_right` and `update()` method to check the status of the `moving_right` flag.
Change `alien_invasion.py`:
```python
def run_game(self):
"""Start the main loop for the game"""
while True:
self._check_events()
self.ship.update()
self._update_screen()
def _check_events(self):
"""Respond to keypresses and mouse events."""
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
elif event.type == pygame.KEYDOWN:
if event.key == pygame.K_RIGHT:
self.ship.moving_right = True
elif event.type == pygame.KEYUP:
if event.key == pygame.K_RIGHT:
self.ship.moving_right = False
```
Change `ship.py`:
```python
def __init__(self, ai_game):
"""Initialize the ship and set its starting position"""
self.screen = ai_game.screen
self.screen_rect = ai_game.screen.get_rect()
# Load the ship image and get its rect
self.image = pygame.image.load('ship.bmp')
self.rect = self.image.get_rect()
# Start each new ship at the bottom center of the screen
self.rect.midbottom = self.screen_rect.midbottom
# Movement flag
self.moving_right = False
def update(self):
"""Update the ship's position based on movement flag"""
if self.moving_right:
self.rect.x += 1
```
### Moving Both Left and Right
Apply the same logic on left movement
### Adjusting the Ship's Speed
1. Add `ship_speed` attribute to the `Settings` class
2. Modify `update()` & `__init__` method of `Ship`, so it move by defined speed
```python
class Settings:
"""A class to store all settings for Alien Invasion"""
def __init__(self):
"""Initialize the game's settings."""
# Screen settings
self.screen_width = 1200
self.screen_height = 800
self.bg_color = (230,230,230)
# Ship settings
self.ship_speed = 1.5
```
Modify `ship.py`
```python
def __init__(self, ai_game):
"""Initialize the ship and set its starting position"""
self.screen = ai_game.screen
self.screen_rect = ai_game.screen.get_rect()
self.settings = ai_game.settings
# Load the ship image and get its rect
self.image = pygame.image.load('ship.bmp')
self.rect = self.image.get_rect()
# Start each new ship at the bottom center of the screen
self.rect.midbottom = self.screen_rect.midbottom
# Store a decimal value for the ship's horizontal position
self.x = float(self.rect.x)
# Movement flag
self.moving_right = False
self.moving_left = False
def update(self):
"""Update the ship's position based on movement flag"""
# Update the ship's x value, not the rect
if self.moving_right:
self.rect.x += self.settings.ship_speed
if self.moving_left:
self.rect.x -= self.settings.ship_speed
```
### Limiting the Ship's Range
Add limit of ship's range
```python
def update(self):
"""Update the ship's position based on movement flag"""
# Update the ship's x value, not the rect
if self.moving_right and self.rect.right < self.screen_rect.right:
self.rect.x += self.settings.ship_speed
if self.moving_left and self.rect.left > 0:
self.rect.x -= self.settings.ship_speed
```
### Refactoring _check_events()
As `_check_events()` is becoming lengthy, we should break/refactor it.
```python
def _check_events(self):
"""Respond to keypresses and mouse events."""
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
elif event.type == pygame.KEYDOWN:
self._check_keydown_events(event)
elif event.type == pygame.KEYUP:
self._check_keyup_events(event)
def _check_keydown_events(self, event):
"""Respond to keypresses"""
if event.key == pygame.K_RIGHT:
self.ship.moving_right = True
elif event.key == pygame.K_LEFT:
self.ship.moving_left = True
def _check_keyup_events(self, event):
"""Respond to key releases"""
if event.key == pygame.K_RIGHT:
self.ship.moving_right = False
elif event.key == pygame.K_LEFT:
self.ship.moving_left = False
```
### Pressing Q to Quit
* use `pygame.K_q` key event (q) to exit program
```python
def _check_keydown_events(self, event):
"""Respond to keypresses"""
if event.key == pygame.K_RIGHT:
self.ship.moving_right = True
elif event.key == pygame.K_LEFT:
self.ship.moving_left = True
elif event.key == pygame.K_q:
sys.exit()
```
### Running the Game in Fullscreen Mode
To run the game in fullscreen mode
```python
class AlienInvasion:
"""Overall class to manage game assets and behaviour"""
def __init__(self):
"""Initialize the game, and create game resources."""
pygame.init()
self.settings = Settings()
# self.screen = pygame.display.set_mode((self.settings.screen_width, self.settings.screen_height))
self.screen = pygame.display.set_mode((0,0), pygame.FULLSCREEN)
self.settings.screen_width = self.screen.get_rect().width
self.settings.screen_height = self.screen.get_rect().height
pygame.display.set_caption("Alien Invasion")
self.ship = Ship(self)
```
## Shooting Bullets
Write code that fires a bullet, which is represented by a small rectangle, when the player presses the spacebar.
### Adding the Bullet Settings
```python
def __init__(self):
"""Initialize the game's settings."""
# Screen settings
...
# Ship settings
...
# Bullet settings
self.bullet_speed = 1.0
self.bullet_width = 3
self.bullet_height = 15
self.bullet_color = (60,60,60)
```
`bullet.py` module
```python
import pygame
from pygame.sprite import Sprite
class Bullet(Sprite):
"""
A class to manage bullets fired from the ship
"""
def __init__(self, ai_game):
"""Create a bullet object at the ship's current position."""
super().__init__()
self.screen = ai_game.screen
self.settings = ai_game.settings
self.color = self.settings.bullet_color
# Create a bullet rect at (0,0) and then set correct position
self.rect = pygame.Rect(0,0,self.settings.bullet_width, self.settings.bullet_height)
self.rect.midtop = ai_game.ship.rect.midtop
# Store the bullet's position as a decimal value
self.y = float(self.rect.y)
```
* `self.rect = ...` created bullet's `rect` attribute.
* First, initialize at `(0,0)`, with width/height stored in `self.settings`
* Then, move it to the correct location via `self.rect.midtop`, as the bullet's position depends on the ship's position
Then add `update()` & `draw_bullet()` for Bullet class
```python
def update(self):
"""Move the bullet up the screen"""
# Update the decimal position of the bullet
self.y -= self.settings.bullet_speed
# Update the rect position
self.rect.y = self.y # When a bullet is fired, it moves up the screen
def draw_bullet(self):
"""Draw the bullet to the screen"""
pygame.draw.rect(self.screen, self.color, self.rect)
```
### Storing Bullets in a Group
After defining the `Bullet` class and its necessary settings, we can write code to fire a bullet each time the player presses the spacebar.
First, we'll create a group in `AlienInvasion` to store all the live bullets, so we can manage the bullets that have already been fired.
`pygame.sprite.Group` class behave like a list with some extra functionality that's helpful when building games. So we directly draw the group (instead of individual bullets) to the screen.
`alien_invasion.py`
```python
def __init__(self):
...
self.ship = Ship(self)
self.bullets = pygame.sprite.Group()
...
def run_game(self):
"""Start the main loop for the game"""
while True:
self._check_events()
self.ship.update()
self.bullets.update() # initiate the bullets group
self._update_screen()
```
### Firing Bullets
1. Add key press event in `_check_keydown_events(self,event)`, which will trigger `_fire_bullet()` by `K_SPACE`
2. Create function `_fire_bullet(self)`
3. Add bullets group's drawing action in `_update_screen()`
```python
from bullet import Bullet
class AlienInvasion:
def _check_keydown_events(self, event):
"""Respond to keypresses"""
...
elif event.key == pygame.K_q:
sys.exit()
elif event.key == pygame.K_SPACE:
self._fire_bullet()
def _check_keyup_events(self, event):
...
def _fire_bullet(self):
"""Create a new bullet and add it to the bullets group"""
new_bullet = Bullet(self)
self.bullets.add(new_bullet)
def _update_screen(self):
"""Update images on the screen, and flip to the new screen"""
...
for bullet in self.bullets.sprites():
bullet.draw_bullet()
pygame.display.flip()
```
### Deleting Old Bullets
Currently, bullets don't delete themselves after moving out of frame. Only their y-coordinate values grow increasingly negative.
* Con: bullets continue to consume memory and processing power.
Solution: need recycle these objects during running the game
```python
def run_game(self):
"""Start the main loop for the game"""
while True:
...
# Delete bullets out of screen
for bullet in self.bullets.copy():
if bullet.rect.bottom <= 0:
self.bullets.remove(bullet)
print(len(self.bullets))
```
### Limiting the Number of Bullets
To limit the number of bullets.
```python
class Settings:
"""A class to store all settings for Alien Invasion"""
def __init__(self):
"""Initialize the game's settings."""
...
self.bullet_allowed = 3
```
Modify `AlienInvasion` class as shown below
```python
class AlienInvasion:
"""Overall class to manage game assets and behaviour"""
...
def _fire_bullet(self):
"""Create a new bullet and add it to the bullets group"""
if len(self.bullets) < self.settings.bullets_allowed:
new_bullet = Bullet(self)
self.bullets.add(new_bullet)
```
### Creating the _update_bullets() Method
Need refactor `run_game` function in `AlienInvasion` class again, to make bullets update and deletion independent of `run_game()`
```python
...
class AlienInvasion:
"""Overall class to manage game assets and behaviour"""
def run_game(self):
"""Start the main loop for the game"""
while True:
self._check_events()
self.ship.update()
self._update_bullets()
self._update_screen()
def _update_bullets(self):
"""Update position of bullets and get rid of old bullets"""
# Update bullet positions.
self.bullets.update()
# Delete bullets out of screen
for bullet in self.bullets.copy():
if bullet.rect.bottom <= 0:
self.bullets.remove(bullet)
print(len(self.bullets))
...
```

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import sys
import pygame
from settings import Settings
from ship import Ship
from bullet import Bullet
class AlienInvasion:
"""Overall class to manage game assets and behaviour"""
def __init__(self):
"""Initialize the game, and create game resources."""
pygame.init()
self.settings = Settings()
self.screen = pygame.display.set_mode((self.settings.screen_width, self.settings.screen_height)) # Use default screen width/height
# self.screen = pygame.display.set_mode((0,0), pygame.FULLSCREEN) # Use full screen
self.settings.screen_width = self.screen.get_rect().width
self.settings.screen_height = self.screen.get_rect().height
pygame.display.set_caption("Alien Invasion")
self.ship = Ship(self)
self.bullets = pygame.sprite.Group() #
def run_game(self):
"""Start the main loop for the game"""
while True:
self._check_events()
self.ship.update()
self._update_bullets()
self._update_screen()
def _check_events(self):
"""Respond to keypresses and mouse events."""
for event in pygame.event.get():
if event.type == pygame.QUIT:
sys.exit()
elif event.type == pygame.KEYDOWN:
self._check_keydown_events(event)
elif event.type == pygame.KEYUP:
self._check_keyup_events(event)
def _check_keydown_events(self, event):
"""Respond to keypresses"""
if event.key == pygame.K_RIGHT:
self.ship.moving_right = True
elif event.key == pygame.K_LEFT:
self.ship.moving_left = True
elif event.key == pygame.K_q:
sys.exit()
elif event.key == pygame.K_SPACE:
self._fire_bullet()
def _check_keyup_events(self, event):
"""Respond to key releases"""
if event.key == pygame.K_RIGHT:
self.ship.moving_right = False
elif event.key == pygame.K_LEFT:
self.ship.moving_left = False
def _fire_bullet(self):
"""Create a new bullet and add it to the bullets group"""
if len(self.bullets) < self.settings.bullets_allowed:
new_bullet = Bullet(self)
self.bullets.add(new_bullet)
def _update_bullets(self):
"""Update position of bullets and get rid of old bullets"""
# Update bullet positions.
self.bullets.update()
# Delete bullets out of screen
for bullet in self.bullets.copy():
if bullet.rect.bottom <= 0:
self.bullets.remove(bullet)
print(len(self.bullets))
def _update_screen(self):
"""Update images on the screen, and flip to the new screen"""
self.screen.fill(self.settings.bg_color)
self.ship.blitme()
for bullet in self.bullets.sprites():
bullet.draw_bullet()
pygame.display.flip()
if __name__ == '__main__':
ai = AlienInvasion()
ai.run_game()

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import pygame
from pygame.sprite import Sprite
class Bullet(Sprite):
"""
A class to manage bullets fired from the ship
"""
def __init__(self, ai_game):
"""Create a bullet object at the ship's current position."""
super().__init__()
self.screen = ai_game.screen
self.settings = ai_game.settings
self.color = self.settings.bullet_color
# Create a bullet rect at (0,0) and then set correct position
self.rect = pygame.Rect(0,0,self.settings.bullet_width, self.settings.bullet_height)
self.rect.midtop = ai_game.ship.rect.midtop
# Store the bullet's position as a decimal value
self.y = float(self.rect.y)
def update(self):
"""Move the bullet up the screen"""
# Update the decimal position of the bullet
self.y -= self.settings.bullet_speed
# Update the rect position
self.rect.y = self.y # When a bullet is fired, it moves up the screen
def draw_bullet(self):
"""Draw the bullet to the screen"""
pygame.draw.rect(self.screen, self.color, self.rect)

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class Settings:
"""A class to store all settings for Alien Invasion"""
def __init__(self):
"""Initialize the game's settings."""
# Screen settings
self.screen_width = 1200
self.screen_height = 800
self.bg_color = (230,230,230)
# Ship settings
self.ship_speed = 1.5
# Bullet settings
self.bullet_speed = 1.0
self.bullet_width = 3
self.bullet_height = 15
self.bullet_color = (60,60,60)
self.bullets_allowed = 3

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import pygame
class Ship:
"""A class to manage the ship."""
def __init__(self, ai_game):
"""Initialize the ship and set its starting position"""
self.screen = ai_game.screen
self.screen_rect = ai_game.screen.get_rect()
self.settings = ai_game.settings
# Load the ship image and get its rect
self.image = pygame.image.load('ship.bmp')
self.rect = self.image.get_rect()
# Start each new ship at the bottom center of the screen
self.rect.midbottom = self.screen_rect.midbottom
# Store a decimal value for the ship's horizontal position
self.x = float(self.rect.x)
# Movement flag
self.moving_right = False
self.moving_left = False
def update(self):
"""Update the ship's position based on movement flag"""
# Update the ship's x value, not the rect
if self.moving_right and self.rect.right < self.screen_rect.right:
self.rect.x += self.settings.ship_speed
if self.moving_left and self.rect.left > 0:
self.rect.x -= self.settings.ship_speed
def blitme(self):
"""Draw the ship at its current location"""
self.screen.blit(self.image,self.rect)