Change the orbit target without move the camera

[happydpc]

I have a cad model manipulated by trackball crate, it works nice. But when I want to change the orbit center, the camera moves to forwad to the object target soon. I want to keep camera static when change the target. I used this function to change target:

	pub fn set_target(&mut self, target: Point3<N>){
			let eye = self.eye();
		self.pos = target;
		self.zat = (self.pos - eye).norm();
	}

[n3vu0r]

Hm, the current behavior of set_target seems wrong, also its documentation is misleading. This should be fixed. Does the following implementation work for you?

	/// Sets target position in world space preserving eye position inclusive its roll attitude.
	pub fn set_target(&mut self, pos: Point3<N>) {
		let eye = self.eye();
		let (new_dir, zat) = Unit::new_and_get(pos - eye);
		let old_dir = Unit::new_normalize(self.pos - eye);
		let rot = UnitQuaternion::rotation_between_axis(&old_dir, &new_dir)
			.unwrap_or_else(|| UnitQuaternion::from_axis_angle(&self.yaw_axis(), N::pi()));
		let rot = rot * self.rot;
		*self = Self { pos, rot, zat }
	}

[happydpc]

Have tried yet myself, with this rot, still moving to the center of the view. that's trange, can't figure out what's wrong.

UnitQuaternion::rotation_between_axis(&old_dir, &new_dir)

[n3vu0r]

Ok, maybe I misunderstood you. Do you just want to move (translate) your cad model around? This can be achieved with the slide method. Try it with slide(new_target - old_target) or maybe slide(old_target - new_target).

[happydpc]

I want to keep the camera static, when changing the orbit center. When a object clicked, the orbit center is just assigned by the object center, no camera move. But now the camera moves with a click.

[n3vu0r]

The camera itself cannot store an orbit center (i.e. target) without looking at it. If you want to assign a new target without moving the camera, you have to store the new target separately and only apply it when you want the camera to move.

The camera stores three elements:

• pos: Point3: Target position in world space (where the camera is looking to).
• rot: Quaternion: Eye rotation from camera to world space around pos. In camera space, the eye is always at Point3::new(N::zero(), N::zero(), zat).
• zat: N: Distance from pos to eye, the radius of the orbit.

[happydpc]

Oh I see, I can use the second target when orbiting. But the logic will be complicated. If I can make the new look matrix just as it should be. The camera may mot move.

[n3vu0r]

Have you found a solution? I would try to use the Bevy ECS to store the target assignment as part of the camera bundle which can then be reassigned when clicking an object.

[happydpc]

Havent solved yet.