def collide_circle(left, right):
"""detect collision between two sprites using circles
pygame.sprite.collide_circle(left, right): return bool
Tests for collision between two sprites by testing whether two circles
centered on the sprites overlap. If the sprites have a "radius" attribute,
then that radius is used to create the circle; otherwise, a circle is
created that is big enough to completely enclose the sprite's rect as
given by the "rect" attribute. This function is intended to be passed as
a collided callback function to the *collide functions. Sprites must have a
"rect" and an optional "radius" attribute.
New in pygame 1.8.0
"""
xdistance = left.rect.centerx - right.rect.centerx
ydistance = left.rect.centery - right.rect.centery
distancesquared = xdistance ** 2 + ydistance ** 2
if hasattr(left, 'radius'):
leftradius = left.radius
else:
leftrect = left.rect
# approximating the radius of a square by using half of the diagonal,
# might give false positives (especially if its a long small rect)
leftradius = 0.5 * ((leftrect.width ** 2 + leftrect.height ** 2) ** 0.5)
# store the radius on the sprite for next time
setattr(left, 'radius', leftradius)
if hasattr(right, 'radius'):
rightradius = right.radius
else:
rightrect = right.rect
# approximating the radius of a square by using half of the diagonal
# might give false positives (especially if its a long small rect)
rightradius = 0.5 * ((rightrect.width ** 2 + rightrect.height ** 2) ** 0.5)
# store the radius on the sprite for next time
setattr(right, 'radius', rightradius)
return distancesquared <= (leftradius + rightradius) ** 2
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