位图旋转是一项计算量相当大的操作。你的代码变慢了，因为它每次更新都会旋转图像，每次都为每个精灵执行大量的数学运算。
在 sprite 构造函数中预先旋转位图是可能的（也很方便），然后简单地将生成的图像放入缓存中。然后，代码无需执行旋转计算，只需确定将哪些缓存图像分配给sprite.image.
这种方法的问题之一是程序员必须决定要构建多少预先生成的旋转。在下面的示例中，我使用整数角度来设置旋转，因此这强制了 360 帧的理论上限。我可以想象在类似矢量的游戏中，程序员可能需要亚度旋转，但这是另一个答案。如果您查看历史旋转位图游戏，通常只使用几个角度，可能是 8 步（360 / 8 → 45°）。无论如何，我的示例使用 15° 角，提供 24 步，这似乎很多！如果您在嵌入式空间中工作，或使用大型位图，则使用的内存可能会成为考虑因素。显然，如果您有许多相同的精灵，理想情况下它们应该共享缓存的图像。这不是本示例的工作方式。
此示例代码还执行基于位图掩码的碰撞（与简单的矩形碰撞相反），因此位图掩码也需要旋转。
import pygame
import random
# Window size
WINDOW_WIDTH = 400
WINDOW_HEIGHT = 400
FPS = 60
# background colours
INKY_BLACK = ( 0, 0, 0)
class MovingSprite( pygame.sprite.Sprite ):
ANGLE_STEP = 15 # degrees, makes 360/ANGLE_STEP frames
def __init__( self, bitmap ):
pygame.sprite.Sprite.__init__( self )
self.rect = bitmap.get_rect()
self.rect.center = ( random.randrange( 0, WINDOW_WIDTH ), random.randrange( 0, WINDOW_HEIGHT ) )
self.crashing = False
# start with zero rotation
self.rotation = 0
self.rotations = [ bitmap ]
self.masks = [ pygame.mask.from_surface( bitmap ) ]
self.angle_slots = 360 // self.ANGLE_STEP
# pre-compute all the rotated images, and bitmap collision masks
for i in range( 1, self.angle_slots ):
rotated_image = pygame.transform.rotate( bitmap, self.ANGLE_STEP * i )
self.rotations.append( rotated_image )
self.masks.append( pygame.mask.from_surface( rotated_image ) )
self._setRotationImage( 0 ) # sets initial image, mask & rect
def rotateTo( self, angle ):
# If the given angle is not an exact point we have, round to nearest
if ( angle % self.ANGLE_STEP != 0 ):
angle = round( angle / self.ANGLE_STEP ) * self.ANGLE_STEP
rot_index = ( angle // self.ANGLE_STEP )
# set the pre-rotated image
self._setRotationImage( rot_index )
def rotateRight( self ):
if ( self.rotation == 0 ):
self._setRotationImage( self.angle_slots - 1 )
else:
self._setRotationImage( self.rotation - 1 )
def rotateLeft( self ):
if ( self.rotation == self.angle_slots - 1 ):
self._setRotationImage( 0 )
else:
self._setRotationImage( self.rotation + 1 )
def _setRotationImage( self, rot_index ):
rot_index %= self.angle_slots
self.rotation = rot_index
# Select the pre-rotated image & mash
self.image = self.rotations[ rot_index ]
self.mask = self.masks[ rot_index ]
# We need to preserve the centre-poisiton of the bitmap,
# as rotated bitmaps will (probably) not be the same size as the original
centerx = self.rect.centerx
centery = self.rect.centery
self.rect = self.image.get_rect()
self.rect.center = ( centerx, centery )
def newPosition( self ):
# Wander Around
if ( not self.crashing ):
self.rect.x += random.randrange( -2, 3 )
self.rect.y += random.randrange( -2, 3 )
else:
self.rect.y += 3
def crash( self ):
self.crashing = True
def update( self ):
self.newPosition()
if ( self.rect.y > WINDOW_HEIGHT ):
self.kill()
elif ( self.crashing == True ):
# rotate as we fall
self.rotateRight()
### MAIN
pygame.init()
pygame.font.init()
SURFACE = pygame.HWSURFACE|pygame.DOUBLEBUF|pygame.RESIZABLE
WINDOW = pygame.display.set_mode( ( WINDOW_WIDTH, WINDOW_HEIGHT ), SURFACE )
pygame.display.set_caption("Sprite Rotation Example")
# Load resource images
sprite_image = pygame.image.load( "tiny_alien_space.png" )#.convert_alpha()
# Make some sprites from game-mode
SPRITES = pygame.sprite.Group() # a group, for a single sprite
for i in range( 50 ):
SPRITES.add( MovingSprite( sprite_image ) )
clock = pygame.time.Clock()
done = False
while not done:
# Handle user-input
for event in pygame.event.get():
if ( event.type == pygame.QUIT ):
done = True
elif ( event.type == pygame.KEYDOWN ):
if ( event.unicode == '+' or event.scancode == pygame.K_PLUS ):
# Pressing '+' adds a new sprite
SPRITES.add( MovingSprite( sprite_image ) )
# Handle continuous-keypresses, but only in playing mode
keys = pygame.key.get_pressed()
if ( keys[pygame.K_UP] ):
print("up")
elif ( keys[pygame.K_DOWN] ):
print("down")
elif ( keys[pygame.K_LEFT] ):
print("left")
elif ( keys[pygame.K_RIGHT] ):
print("right")
elif ( keys[pygame.K_ESCAPE] ):
# [Esc] exits too
done = True
# Repaint the screen
SPRITES.update() # re-position the game sprites
WINDOW.fill( INKY_BLACK )
SPRITES.draw( WINDOW ) # draw the game sprites
# Determine collisions - simple rect-based collision first
single_group = pygame.sprite.GroupSingle()
for s in SPRITES:
single_group.sprite = s
collisions = pygame.sprite.groupcollide( single_group, SPRITES, False, False )
# Now double-check collisions with the bitmap-mask to get per-pixel accuracy
for other in collisions[ s ]:
if ( other != s ): # we don't collide with ourselves
# Second step, do more complex collision detection
# using the sprites mask
if ( pygame.sprite.collide_mask( s, other ) ):
#print("Collision")
s.crash( )
other.crash( )
pygame.display.flip()
# Update the window, but not more than 60fps
clock.tick_busy_loop( FPS )
pygame.quit()
注意：此动画 .GIF 的帧率远低于屏幕版本，因此不能反映示例的真实操作。