[Solved] Problems orienting camera with extreme P values

Scripting Issues
1

Hey everyone,

I’m writing a program where the user flies a camera and as such can point it any direction. My cameras are parented to render as otherwise my RoamingRalph forward-movement matrix hack refuses to work. To do my “rotations” (i.e. angling the camera upwards, downwards, leftwards and rightward) I’m setting the H and P of the camera. While the camera is orientated “normally” (i.e. with HPR of (0,0,0) ) this works as I expected: changing P rotates the camera to face upwards or downwards and changing H rotates the camera leftwards or rightwards.

However, if I change P this behavior changes. If I set P to 90 my upward and downward rotations remain functional but changes in H creates only a rotation in a circle, not towards the camera’s left and right as desired.

How do I fix this? I’ve discovered that if I set the camera’s R to 90 then change it’s P value I can do rotations to the left and right but for some reason I don’t seem to be able to implement this with tasks and this seems like quite a hack to do something so simple.

Here is the relevant bits of code, I’d appreciate any nudge in the right direction! It’s structured very much like the RoamingRalph demo as I thought that was quite a clean way to organise the code.


# Snippet from init
def __init__(self):
		self.camera = self.makeCamera(self.win)
		self.camera.reparentTo(render)

def move(self, task):
		"""
		A task that is continously called that moves the active camera in the 
		directions given by the states set with set_key.
		"""
		cam = self.camera
		# Left and Right rotation
		if self.key_map["left"] != 0: 
			cam.setH(cam.getH() +100 * globalClock.getDt())
		if self.key_map["right"] != 0:
			cam.setH(cam.getH() -100 * globalClock.getDt())
		
		# Upward and Downward rotation
		if self.key_map["up"] != 0:
			cam.setP(cam.getP() +100 * globalClock.getDt())
		if self.key_map["down"] != 0:
			cam.setP(cam.getP() -100 * globalClock.getDt())

Edit: fixing my embarrassing it’s/its mistake

2

You might be the victim of gimbal lock, which basically means the hpr math doesn’t work at extreme positions. Try using quaternions.

3

Another approach is to use relative transforms. Instead of using simple addition, use a rotation relative to yourself. Replace:

cam.setH(cam.getH() +100 * globalClock.getDt())

with:

cam.setH(cam, 100 * globalClock.getDt())

David

4

This worked perfectly, thanks again David!