SceneKit smooth camera movement

Question

What is the standard method for smooth camera movement within SceneKit (OpenGL)? Manually changing x,y isn't smooth enough, yet using CoreAnimation creates "pulsing" movement. The docs on SceneKit seem to be very limited so any examples would be appreciated, I'm currently doing this:

- (void)keyDown:(NSEvent *)theEvent {
    int key = [theEvent keyCode];
    int x = cameraNode.position.x;
    int y = cameraNode.position.y;
    int z = cameraNode.position.z;
    int speed = 4;
    if (key==123) {//left
        x-=speed;
    } else if (key==124) {//right
        x+=speed;
    } else if (key==125) {//down
        y-=speed;
    } else if (key==126) {//up
        y+=speed;
    }
    //move the camera
    [SCNTransaction begin];
    [SCNTransaction setAnimationDuration: 1.0];
    // Change properties
    cameraNode.position = SCNVector3Make(x, y, z);
    [SCNTransaction commit];
}

Answer 1

To minimise the pulsing movements (due to the key repeat) you can use an "easeOut" timingFunction:

//move the camera
[SCNTransaction begin];
[SCNTransaction setAnimationDuration: 1.0];
[SCNTransaction setAnimationTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut]];
// Change properties
cameraNode.position = SCNVector3Make(x, y, z);
[SCNTransaction commit];

That said, the best thing to do here is probably to manage a target position (a vector3) yourself and update the position of the camera at every frame to go to this target smoothly.

Answer 2

I've been experimenting with this. The best I've found so far is to record the state of the input keys in internal state, modified by keyDown: and keyUp:, and run an NSTimer to apply them. The timer uses the actual, measured time delta between firings to determine how far to move the camera. That way irregular timings don't have too much effect (and I can call my method to update the camera position at any time without worrying about changing its movement speed).

It takes some work to make this behave correctly, though. keyDown: and keyUp: have some obnoxious behaviours when it comes to game input. For example, repeating keys. Also, they may fire even after your view loses focus or your app goes to the background, if keys are held down across the transition. Etc. Not insurmountable, but annoying.

What I haven't yet done is add acceleration and deceleration, which I think will aid the perception of it being smooth. Otherwise it feels pretty good.