同时在多个SceneKit节点上进行CAAnimation

Question

I am creating an application wherein I am using SceneKit contents in AR app. I have multiple nodes which are being placed at different places in my scene. They may or may not be necessarily be inside one parent node. The user has to choose a correct node, as per challenge set by the application. If the user chooses correct node, the correct node goes through one kind of animation and incorrect ones (may be several) undergo another set of animation. I am accomplishing animations using CAAnimation directly, which is all good. Basically to accomplish this, I am creating an array of all nodes and using them for animation.

DispatchQueue.global(qos: .userInteractive).async { [weak self] in
    for node in (self?.nodesAddedInScene.keys)! {
        for index in 1...node.childNodes.count - 1 {
            if node.childNodes[index].childNodes.first?.name == "target" {
                self?.riseUpSpinAndFadeAnimation(on: node.childNodes[index])
            } else {
                self?.fadeAnimation(on: node.childNodes[index])
            }
        }
    }
}

When user chooses "target" node, that node goes through one set of animation and others go through another set of animations.

RiseUpSpinAndFadeAnimation:

    private func riseUpSpinAndFadeAnimation(on shape: SCNNode) {
        let riseUpAnimation = CABasicAnimation(keyPath: "position")
        riseUpAnimation.fromValue = SCNVector3(shape.position.x, shape.position.y, shape.position.z)
        riseUpAnimation.toValue = SCNVector3(shape.position.x, shape.position.y + 0.5, shape.position.z)

        let spinAnimation = CABasicAnimation(keyPath: "eulerAngles.y")
        spinAnimation.toValue = shape.eulerAngles.y + 180.0
        spinAnimation.autoreverses = true

        let fadeAnimation = CABasicAnimation(keyPath: "opacity")
        fadeAnimation.toValue = 0.0

        let riseUpSpinAndFadeAnimation = CAAnimationGroup()
        riseUpSpinAndFadeAnimation.animations = [riseUpAnimation, fadeAnimation, spinAnimation]
        riseUpSpinAndFadeAnimation.duration = 1.0
        riseUpSpinAndFadeAnimation.fillMode = kCAFillModeForwards
        riseUpSpinAndFadeAnimation.isRemovedOnCompletion = false

        shape.addAnimation(riseUpSpinAndFadeAnimation, forKey: "riseUpSpinAndFade")
    }

FadeAnimation:

private func fadeAnimation(on shape: SCNNode) {
    let fadeAnimation = CABasicAnimation(keyPath: "opacity")
    fadeAnimation.toValue = 0.0
    fadeAnimation.duration = 0.5
    fadeAnimation.fillMode = kCAFillModeForwards
    fadeAnimation.isRemovedOnCompletion = false
    shape.addAnimation(fadeAnimation, forKey: "fade")
}

I expect animations to work out, which they are actually. However, the issue is since the nodes are in an array animation is not being done at the same time for all nodes. There are minute differences in start of animation which actually is leading to not so good UI.

What I am looking for is a logic wherein I can attach animations on all nodes and call these animations together later when let's say the user taps correct node. Arrays don't seem to be a wise choice to me. However, I am afraid if I make all of these nodes child nodes of an empty node and the run animation on that empty node, possibly it would be difficult to manage placement of these child nodes in the first place since they supposed to be kept at random distances and not necessarily close together. Given that this ultimately drives AR experience, it more so becomes a bummer.

Requesting some inputs whether there are methods to attach animation to multiple (selected out of those) object (even if sequentially) but RUN them together. I used shape.addAnimation(fadeAnimation, forKey: "fade") "forKey", can that be made of use in such use case? Any pointers appreciated.

Answer 1

I've had up to fifty SCNNodes animating in perfect harmony by using CAKeyframe animations that are paused (.speed = 0) and setting the animation's time offset (.timeOffset) inside a SCNSceneRendererDelegate "renderer(updateAtTime:)" function.

It's pretty amazing how you can add a paused animation with an time offset every 1/60th of a second for a large number of nodes. Hats off to the SceneKit developers for having so little overhead on adding and removing CAAnimations.

I tried many different CAAnimation/SCNAction techniques before settling on this. In other methods the animations would drift out of sync over time.

Answer 2

Manganese,

I am just taking a guess here or could spark an idea for you :-)

I am focusing on this part of your question: "What I am looking for is a logic wherein I can attach animations on all nodes and call these animations together later when let's say the user taps correct node."

I wonder if SCNTransaction: [ https://developer.apple.com/documentation/scenekit/scntransaction][1] might do the trick

or maybe dispatch.sync or async (totally guessing...but could help) [ https://developer.apple.com/documentation/dispatch][1]

or I am way off the mark :-) just trying to help out....

We all learn by sharing what we know

RAD