How to “crop” SCNAnimationPlayer to a specific start and end time, iOS 11

Question

I have a .dae model with a long animation. The animation includes segments of walking, running, hitting, death, etc. I know the frame numbers of the start and end of each segment. I also know the frame per second rate. So getting the time of the start and end of each segment is pretty easy.

I can get the full animation as a SCNAnimationPlayer object. What I’ve been experimenting with is making a copy of the full animation and then setting the timeOffset and duration of the animation.

let walkPlayer = fullPlayer.copy() as! SCNAnimationPlayer
walkPlayer.stop()
walkPlayer.animation.timeOffset = walk.offset
walkPlayer.animation.duration = walk.duration

I then add the walkPlayer back to the Bip01 node (where I got the full animation from).

I can play the walk easily enough by calling animationPlayer(forKey:"walk")?.play()

I can change the duration and other aspects of the animation easily enough. But the animation always starts at frame 0. Whatever value I put into .timeOffset, it just gets ignored.

How can I play from a start frame to an end frame of an SCNAnimation found in SCNAnimationPlayer?

Answer 1

The key bit was to find

CAAnimation(scnAnimation: animation)

and

SCNAnimation(caAnimation: animation)

Once I found these then I could use CAAnimationGroup to “crop” the full animation.

Here’s my Troll.swift that I was working on. There is, of course, much to do but now I can at least make the poor beast walk and die.

class Troll: SCNNode {
    var body:SCNNode!

    static func timeRange(forStartingAtFrame start:Int, endingAtFrame end:Int, fps:Double = 30) -> (offset:TimeInterval, duration:TimeInterval) {
        let startTime   = self.time(atFrame: start, fps: fps) //TimeInterval(start) / fps
        let endTime     = self.time(atFrame: end, fps: fps) //TimeInterval(end) / fps
        return (offset:startTime, duration:endTime - startTime)
    }

    static func time(atFrame frame:Int, fps:Double = 30) -> TimeInterval {
        return TimeInterval(frame) / fps
    }

    static func animation(from full:CAAnimation, startingAtFrame start:Int, endingAtFrame end:Int, fps:Double = 30) -> CAAnimation {
        let range = self.timeRange(forStartingAtFrame: start, endingAtFrame: end, fps: fps)
        let animation = CAAnimationGroup()
        let sub = full.copy() as! CAAnimation
        sub.timeOffset = range.offset
        animation.animations = [sub]
        animation.duration = range.duration
        return animation
    }


    func load() {

        guard let trollScene = SCNScene(named: "Models.scnassets/troll/troll.dae") else {
            fatalError("Can't load the scene")
        }

        guard let troll_body = trollScene.rootNode.childNode(withName: "troll", recursively: true) else {
            fatalError( "found no troll")
        }

        guard let troll_weapon = trollScene.rootNode.childNode(withName: "troll_weapon", recursively: true) else {
            fatalError( "found no troll_weapon")
        }

        guard let troll_bracelet = trollScene.rootNode.childNode(withName: "troll_bracelet", recursively: true) else {
            fatalError( "found no troll_bracelet")
        }

        guard let bips = trollScene.rootNode.childNode(withName: "Bip01", recursively: true) else {
            fatalError( "found no Bip01")
        }

        guard let fullKey = bips.animationKeys.first else {
            fatalError( "Bip01 got no animation")
        }

        guard let fullPlayer = bips.animationPlayer(forKey: fullKey) else {
            fatalError( "Bip01 got no player for \(fullKey)")
        }
        let fullAnimation = CAAnimation(scnAnimation: fullPlayer.animation)

        self.addChildNode(troll_body)
        self.addChildNode(troll_weapon)
        self.addChildNode(troll_bracelet)
        self.addChildNode(bips)

        self.body = bips
        self.body.removeAllAnimations()

        let walkAnimation = Troll.animation(from: fullAnimation, startingAtFrame: 10, endingAtFrame: 60)
        walkAnimation.repeatCount = .greatestFiniteMagnitude
        walkAnimation.fadeInDuration = 0.3
        walkAnimation.fadeOutDuration = 0.3
        let walkPlayer = SCNAnimationPlayer(animation: SCNAnimation(caAnimation: walkAnimation))
        self.body.addAnimationPlayer(walkPlayer, forKey: "walk")

        let deathAnimation = Troll.animation(from: fullAnimation, startingAtFrame: 1810, endingAtFrame: 1850)
        deathAnimation.isRemovedOnCompletion = false
        deathAnimation.fadeInDuration = 0.3
        deathAnimation.fadeOutDuration = 0.3
        let deathPlayer = SCNAnimationPlayer(animation: SCNAnimation(caAnimation: deathAnimation))
        self.body.addAnimationPlayer(deathPlayer, forKey: "death")

        self.scale     = SCNVector3(0.1,0.1,0.1)

    }

    func walk() {
        print( "+++ walk +++" )
        self.body.animationPlayer(forKey: "walk")?.play()
    }

    func death() {
        print( "+++ death +++" )
        self.body.animationPlayer(forKey: "walk")?.stop(withBlendOutDuration: 0.3)
        self.body.animationPlayer(forKey: "death")?.play()
    }
}