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