Trying to rotate a guided missile in pygame - pygame

Question

Trig is not my strong suit which is why I am having probs trying to get my guided missile to rotate properly. Looks like I have the direction fine although Im still not 100% happy with the movement, so Im hoping by fixing the rotation it will fix that also. Problem is my missiles dont point towards the target (player), and they also flip at a certain point past the target. Heres is the code...the rotations just dont work correctly.
def update(self):
self.calcVect()
self.calcPos()
self.rotate()
self.checkBounds()
self.rect.center = (self.x, self.y)
def calcVect(self):
self.vectX = self.targetX - self.x
self.vectY = self.targetY - self.y
self.length = math.sqrt((self.vectX*self.vectX)+(self.vectY*self.vectY))
self.normX = self.vectX/self.length
self.normY = self.vectY/self.length
self.dx += self.normX*self.power
self.dy += self.normY*self.power
def calcPos(self):
self.x += self.dx*0.2
self.y += self.dy*0.2
def rotate(self):
radians = math.atan2(-self.vectY,self.vectX)
radians %= 2*math.pi
self.dir = math.degrees(radians)
print self.dir
oldCenter = self.rect.center
self.image = pygame.transform.rotate(self.imageMissile, self.dir)
self.rect = self.image.get_rect()
self.rect.center = oldCenter
Working Code
Here is the new working code for the entire class. The expression at the end of this line enabled correct rotations "radians = math.atan2(self.vectX, self.vectY)- math.pi/2" even though the image was horizontal to start with.
class GuidedMissile(pygame.sprite.Sprite):
def __init__(self, source):
pygame.sprite.Sprite.__init__(self)
self.screen = source.screen
self.imageMissile = pygame.image.load("Images/missile.tga").convert()
self.imageMissile.set_colorkey((0,0,255))
self.image = self.imageMissile
self.rect = self.image.get_rect()
self.rect.center = source.rect.midbottom
self.rect.inflate_ip(-15, -5)
self.x, self.y = self.rect.center
self.X, self.Y = self.rect.center
self.dx = 0
self.dy = 0
self.power = 3
self.dir = 0
def update(self):
self.player = goodSpritesOneGRP.sprite
self.targetX, self.targetY = self.player.rect.center
NX, NY = self.calcVect()
self.calcVel(NX, NY)
self.calcPos()
self.rotate()
self.checkBounds()
self.rect.center = (self.x, self.y)
def calcVect(self):
self.vectX = self.targetX - self.x
self.vectY = self.targetY - self.y
self.length = math.sqrt((self.vectX*self.vectX)+(self.vectY*self.vectY))
if self.length == 0:
self.normX = 0
self.normY = 1
else:
self.normX = self.vectX/self.length
self.normY = self.vectY/self.length
return (self.normX, self.normY)
def calcVel(self,NX,NY ):
self.dx += NX*self.power
self.dy += NY*self.power
def calcPos(self):
self.x += self.dx*0.05
self.y += self.dy*0.05
def rotate(self):
radians = math.atan2(self.vectX, self.vectY)- math.pi/2
radians %= 2*math.pi
self.dir = math.degrees(radians)
oldCenter = self.rect.center
self.image = pygame.transform.rotate(self.imageMissile, self.dir)
self.rect = self.image.get_rect()
self.rect.center = oldCenter
def checkBounds(self):
global guidedMissile
screen = self.screen
if self.x > screen.get_width():
self.kill()
guidedMissile -= 1
if self.x < -100:
self.kill()
guidedMissile -= 1
if self.y > screen.get_height() + 100:
self.kill()
guidedMissile -= 1
if self.y < -100:
self.kill()
guidedMissile -= 1

Answer 1

When you call calcPos() you have to recalculate self.vectX and self.vectY, otherwise the missile will not point to the target. And don't forget to check if self.length == 0
You can fix splitting calcVect():
def calcVect(self):
self.vectX = self.targetX - self.x
self.vectY = self.targetY - self.y
self.length = math.sqrt((self.vectX*self.vectX)+(self.vectY*self.vectY))
if self.length != 0:
normX = vectX/self.length
normY = vectY/self.length
# Update velocity
def calcVel(self):
self.dx += self.normX*self.power
self.dy += self.normY*self.power
Then
def update(self):
self.calcVect()
self.calcVel()
self.calcPos()
self.calcVect()
self.rotate()
self.checkBounds()
self.rect.center = (self.x, self.y)
This solution works, but I suggest you to write a generic method calcVectTo(self, target) that returns the unitary vector pointing to (target.x, target.y):
def calcVect(self, target):
vectX = target.x - self.x
vectY = target.y - self.y
length = math.sqrt((vectX*vectX)+(vectY*vectY))
if length == 0:
normX = 0
normY = 1
else
normX = vectX/length
normY = vectY/length
return (normX, normY)
Edit
I did not understand that the target is fixed, now it is much easier: you only need to calculate vect at the construction of the class, moving calcVect from update to __construct (ignore my second implementation of calcVect):
class GuidedMissile(pygame.sprite.Sprite):
def __init__(self, source, target):
...
self.calcVect()
def update(self):
self.calcVel()
self.calcPos()
self.rotate()
self.checkBounds()
self.rect.center = (self.x, self.y)