[英]How do I leave a trail behind a sprite with pygame?
众所周知,如果你移动一个精灵而不在它留下痕迹之前填满屏幕,但是,我想在移动其他东西的同时在我的后面留下一条很酷的痕迹(这意味着我不能简单地停止填满屏幕。提前感谢您的帮助
一种解决方案是创建另一个透明表面(此处称为alpha_surf
),其大小与您使用轨迹 blit 对象的屏幕大小相同。 它需要是一个每像素 alpha 表面,您可以通过传递pygame.SRCALPHA
特殊标志来创建它。
Blit 对象并通过用透明白色填充每一帧来降低alpha_surf
上所有像素的 alpha,并传递pygame.BLEND_RGBA_MULT
标志,以便仅影响 alpha 通道。
import pygame as pg
from pygame.math import Vector2
class Player(pg.sprite.Sprite):
def __init__(self, pos, *groups):
super().__init__(*groups)
self.image = pg.Surface((50, 50), pg.SRCALPHA)
pg.draw.circle(self.image, pg.Color('dodgerblue'), (25, 25), 25)
self.rect = self.image.get_rect(center=pos)
self.vel = Vector2(0, 0)
self.pos = Vector2(pos)
def update(self):
self.pos += self.vel
self.rect.center = self.pos
def main():
pg.init()
screen = pg.display.set_mode((640, 480))
# Blit objects with trails onto this surface instead of the screen.
alpha_surf = pg.Surface(screen.get_size(), pg.SRCALPHA)
clock = pg.time.Clock()
all_sprites = pg.sprite.Group()
player = Player((150, 150), all_sprites)
while True:
for event in pg.event.get():
if event.type == pg.QUIT:
return
elif event.type == pg.KEYDOWN:
if event.key == pg.K_d:
player.vel.x = 5
elif event.key == pg.K_a:
player.vel.x = -5
elif event.key == pg.K_w:
player.vel.y = -5
elif event.key == pg.K_s:
player.vel.y = 5
elif event.type == pg.KEYUP:
if event.key == pg.K_d and player.vel.x > 0:
player.vel.x = 0
elif event.key == pg.K_a and player.vel.x < 0:
player.vel.x = 0
elif event.key == pg.K_w:
player.vel.y = 0
elif event.key == pg.K_s:
player.vel.y = 0
# Reduce the alpha of all pixels on this surface each frame.
# Control the fade speed with the alpha value.
alpha_surf.fill((255, 255, 255, 220), special_flags=pg.BLEND_RGBA_MULT)
all_sprites.update()
screen.fill((20, 50, 80)) # Clear the screen.
all_sprites.draw(alpha_surf) # Draw the objects onto the alpha_surf.
screen.blit(alpha_surf, (0, 0)) # Blit the alpha_surf onto the screen.
pg.display.flip()
clock.tick(60)
if __name__ == '__main__':
main()
pg.quit()
或者,您可以使用不同的 alpha 值创建多个版本的精灵图像,并存储精灵的先前位置。 然后在之前的位置用较低的 alpha 对图像进行 blit。
如果您想创建不同类型的轨迹,例如烟雾,您还可以 blit 其他图像或粒子而不是self.image
。
这是另一个变体,带有单独的、不同的轨迹图像,在精灵的self.image
被self.image
之前被self.image
,因此它会出现在它们下面:
import pygame as pg
from pygame.math import Vector2
class Player(pg.sprite.Sprite):
def __init__(self, pos, *groups):
super().__init__(*groups)
self.image = pg.Surface((50, 70), pg.SRCALPHA)
self.image.fill(pg.Color('sienna1'))
self.rect = self.image.get_rect(center=pos)
# A separate image for the trail (just a single-color circle).
self.trail_image = pg.Surface((40, 40), pg.SRCALPHA)
pg.draw.circle(self.trail_image, pg.Color('dodgerblue'), (20, 20), 20)
self.trail_rect = self.trail_image.get_rect()
self.vel = Vector2(0, 0)
self.pos = Vector2(pos)
def update(self):
self.pos += self.vel
self.rect.center = self.pos
# Update the rect of the trail as well, because we'll blit it there.
self.trail_rect.center = self.rect.center
def main():
pg.init()
screen = pg.display.set_mode((640, 480))
# Blit objects with trails onto this surface instead of the screen.
alpha_surf = pg.Surface(screen.get_size(), pg.SRCALPHA)
clock = pg.time.Clock()
all_sprites = pg.sprite.Group()
sprites_with_trails = pg.sprite.Group()
player = Player((150, 150), all_sprites, sprites_with_trails)
while True:
for event in pg.event.get():
if event.type == pg.QUIT:
return
elif event.type == pg.KEYDOWN:
if event.key == pg.K_d:
player.vel.x = 5
elif event.key == pg.K_a:
player.vel.x = -5
elif event.key == pg.K_w:
player.vel.y = -5
elif event.key == pg.K_s:
player.vel.y = 5
elif event.type == pg.KEYUP:
if event.key == pg.K_d and player.vel.x > 0:
player.vel.x = 0
elif event.key == pg.K_a and player.vel.x < 0:
player.vel.x = 0
elif event.key == pg.K_w:
player.vel.y = 0
elif event.key == pg.K_s:
player.vel.y = 0
# Reduce the alpha of all pixels on this surface each frame.
# Control the fade speed with the alpha value.
alpha_surf.fill((255, 255, 255, 244), special_flags=pg.BLEND_RGBA_MULT)
all_sprites.update()
screen.fill((20, 50, 80)) # Clear the screen.
# Blit the trails onto the alpha_surf.
for sprite in sprites_with_trails:
alpha_surf.blit(sprite.trail_image, sprite.trail_rect)
screen.blit(alpha_surf, (0, 0)) # Blit the alpha_surf onto the screen.
all_sprites.draw(screen) # Draw the objects onto the alpha_surf.
pg.display.flip()
clock.tick(60)
if __name__ == '__main__':
main()
pg.quit()
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