fall_mask.py

"""
Demonstrates some simple platforming using mask collision. Shows the benefit
of using pixel perfect collision detection. When using mask collision
techniques, it is generally best to perfom initial rectangle collision tests
before investing in the more expensive mask detection methods.

Note that this code does not allow the sprite to traverse slopes.
That will be addressed in a future example.

-Written by Sean J. McKiernan 'Mekire'
"""

import os
import sys
import random
import pygame as pg


CAPTION = "Basic Platforming: Pixel Perfect Collision"
SCREEN_SIZE = (700, 500)
BACKGROUND_COLOR = (50, 50, 50)


class _Physics(object):
    """
    A simplified physics class. Using a 'real' gravity function here, though
    it is questionable whether or not it is worth the effort. Compare to the
    effect of gravity in fall_rect and decide for yourself.
    """
    def __init__(self):
        """You can experiment with different gravity here."""
        self.x_vel = self.y_vel = self.y_vel_i = 0
        self.grav = 20
        self.fall = False
        self.time = None

    def physics_update(self):
        """If the player is falling, calculate current y velocity."""
        if self.fall:
            time_now = pg.time.get_ticks()
            if not self.time:
                self.time = time_now
            self.y_vel = self.grav*((time_now-self.time)/1000.0)+self.y_vel_i
        else:
            self.time = None
            self.y_vel = self.y_vel_i = 0


class Player(_Physics, pg.sprite.Sprite):
    """Class representing our player."""
    def __init__(self,location,speed):
        """
        The location is an (x,y) coordinate pair, and speed is the player's
        speed in pixels per frame. Speed should be an integer.
        """
        _Physics.__init__(self)
        pg.sprite.Sprite.__init__(self)
        self.image = PLAYER_IMAGE
        self.mask  = pg.mask.from_surface(self.image)
        self.speed = speed
        self.jump_power = 10
        self.rect = self.image.get_rect(topleft=location)

    def get_position(self, obstacles):
        """Calculate the player's position this frame, including collisions."""
        if not self.fall:
            self.check_falling(obstacles)
        else:
            self.fall = self.check_collisions((0,self.y_vel), 1, obstacles)
        if self.x_vel:
            self.check_collisions((self.x_vel,0), 0, obstacles)

    def check_falling(self, obstacles):
        """If player is not contacting the ground, enter fall state."""
        self.rect.move_ip((0,1))
        collisions = pg.sprite.spritecollide(self, obstacles, False)
        collidable = pg.sprite.collide_mask
        if not pg.sprite.spritecollideany(self, collisions, collidable):
            self.fall = True
        self.rect.move_ip((0,-1))

    def check_collisions(self, offset, index, obstacles):
        """
        This function checks if a collision would occur after moving offset
        pixels.  If a collision is detected position is decremented by one
        pixel and retested. This continues until we find exactly how far we can
        safely move, or we decide we can't move.
        """
        unaltered = True
        self.rect.move_ip(offset)
        collisions = pg.sprite.spritecollide(self, obstacles, False)
        collidable = pg.sprite.collide_mask
        while pg.sprite.spritecollideany(self, collisions, collidable):
            self.rect[index] += (1 if offset[index]<0 else -1)
            unaltered = False
        return unaltered

    def check_keys(self, keys):
        """Find the player's self.x_vel based on currently held keys."""
        self.x_vel = 0
        if keys[pg.K_LEFT] or keys[pg.K_a]:
            self.x_vel -= self.speed
        if keys[pg.K_RIGHT] or keys[pg.K_d]:
            self.x_vel += self.speed

    def jump(self):
        """Called when the user presses the jump button."""
        if not self.fall:
            self.y_vel_i = -self.jump_power
            self.fall = True

    def update(self, obstacles, keys):
        """Everything we need to stay updated."""
        self.check_keys(keys)
        self.get_position(obstacles)
        self.physics_update()

    def draw(self,surface):
        """Blit the player to the target surface."""
        surface.blit(self.image, self.rect)


class Block(pg.sprite.Sprite):
    """A class representing solid obstacles."""
    def __init__(self, location):
        """The location argument is an (x,y) coordinate pair."""
        pg.sprite.Sprite.__init__(self)
        self.make_image()
        self.mask = pg.mask.from_surface(self.image)
        self.rect = pg.Rect(location, (50,50))

    def make_image(self):
        """Something pretty to look at."""
        color = [random.randint(0,255) for _ in range(3)]
        self.image = pg.Surface((50,50)).convert_alpha()
        self.image.fill(color)
        self.image.blit(SHADE_IMG, (0,0))


class Control(object):
    """Class for managing event loop and game states."""
    def __init__(self):
        """Nothing to see here folks. Move along."""
        self.screen = pg.display.get_surface()
        self.clock = pg.time.Clock()
        self.fps = 60.0
        self.keys = pg.key.get_pressed()
        self.done = False
        self.player = Player((50,-25), 4)
        self.obstacles = self.make_obstacles()

    def make_obstacles(self):
        """Adds some arbitrarily placed obstacles to a sprite.Group."""
        obstacles = [Block((400,400)), Block((300,270)), Block((150,170))]
        obstacles += [Block((500+50*i,220)) for i in range(3)]
        for i in range(12):
            obstacles.append(Block((50+i*50,450)))
            obstacles.append(Block((100+i*50,0)))
            obstacles.append(Block((0,50*i)))
            obstacles.append(Block((650,50*i)))
        return pg.sprite.Group(obstacles)

    def event_loop(self):
        """We can always quit, and the player can sometimes jump."""
        for event in pg.event.get():
            if event.type == pg.QUIT or self.keys[pg.K_ESCAPE]:
                self.done = True
            elif event.type == pg.KEYDOWN:
                if event.key == pg.K_SPACE:
                    self.player.jump()

    def update(self):
        """Update held keys and the player."""
        self.keys = pg.key.get_pressed()
        self.player.update(self.obstacles, self.keys)

    def draw(self):
        """Draw all necessary objects to the display surface."""
        self.screen.fill(BACKGROUND_COLOR)
        self.obstacles.draw(self.screen)
        self.player.draw(self.screen)

    def display_fps(self):
        """Show the programs FPS in the window handle."""
        caption = "{} - FPS: {:.2f}".format(CAPTION, self.clock.get_fps())
        pg.display.set_caption(caption)

    def main_loop(self):
        """As simple as it gets."""
        while not self.done:
            self.event_loop()
            self.update()
            self.draw()
            pg.display.update()
            self.clock.tick(self.fps)
            self.display_fps()


if __name__ == "__main__":
    os.environ['SDL_VIDEO_CENTERED'] = '1'
    pg.init()
    pg.display.set_caption(CAPTION)
    pg.display.set_mode(SCREEN_SIZE)
    PLAYER_IMAGE = pg.image.load("smallface.png").convert_alpha()
    SHADE_IMG = pg.image.load("shader.png").convert_alpha()
    run_it = Control()
    run_it.main_loop()
    pg.quit()
    sys.exit()