SKShapeNode - Animate color change

Question

I'm working on a game with SpriteKit. I'm drawing a shape with SKShapeNode. Now I want to animate its colour change but the SKActions is not working for SKShapeNode. Is there any way to do this or I have to use a different approach?

Thank you.

EDIT:

Thanks to LearnCocos2D I was able to come up with this quick (and totally not perfect) solution.

int groundChangeInterval = 5;
SKColor *originalColor = [SKColor colorWithRed:0.92 green:0.87 blue:0.38 alpha:1.0];
SKColor *finalColor = [SKColor colorWithRed:0.29 green:0.89 blue:0.31 alpha:1.0];

CGFloat red1 = 0.0, green1 = 0.0, blue1 = 0.0, alpha1 = 0.0;
[originalColor getRed:&red1 green:&green1 blue:&blue1 alpha:&alpha1];

CGFloat red2 = 0.0, green2 = 0.0, blue2 = 0.0, alpha2 = 0.0;
[finalColor getRed:&red2 green:&green2 blue:&blue2 alpha:&alpha2];

SKAction *changeGroundColor = [SKAction customActionWithDuration:groundChangeInterval actionBlock:^(SKNode *node, CGFloat elapsedTime) {
    CGFloat step = elapsedTime/groundChangeInterval;

    CGFloat red3 = 0.0, green3 = 0.0, blue3 = 0.0;
    red3 = red1-(red1-red2)*step;
    green3 = green1-(green1-green2)*step;
    blue3 = blue1-(blue1-blue2)*step;

    [(SKShapeNode*)node setFillColor:[SKColor colorWithRed:red3 green:green3 blue:blue3 alpha:1.0]];
    [(SKShapeNode*)node setStrokeColor:[SKColor colorWithRed:red3 green:green3 blue:blue3 alpha:1.0]];
}];

I only needed to fade two specific colours so it is not a universal solution but it is enough for now.

Thanks

Answer 1

Updated for Swift 4.2

This the common code that you need to place in and extension file or something of the sort.

func lerp(a : CGFloat, b : CGFloat, fraction : CGFloat) -> CGFloat
{
    return (b-a) * fraction + a
}

struct ColorComponents {
    var red = CGFloat(0)
    var green = CGFloat(0)
    var blue = CGFloat(0)
    var alpha = CGFloat(0)
}

extension UIColor {
    func toComponents() -> ColorComponents {
        var components = ColorComponents()
        getRed(&components.red, green: &components.green, blue: &components.blue, alpha: &components.alpha)
        return components
    }
}

extension SKAction {
    static func colorTransitionAction(fromColor : UIColor, toColor : UIColor, duration : Double = 0.4) -> SKAction
    {
        return SKAction.customAction(withDuration: duration, actionBlock: { (node : SKNode!, elapsedTime : CGFloat) -> Void in
            let fraction = CGFloat(elapsedTime / CGFloat(duration))
            let startColorComponents = fromColor.toComponents()
            let endColorComponents = toColor.toComponents()
            let transColor = UIColor(red: lerp(a: startColorComponents.red, b: endColorComponents.red, fraction: fraction),
                                     green: lerp(a: startColorComponents.green, b: endColorComponents.green, fraction: fraction),
                                     blue: lerp(a: startColorComponents.blue, b: endColorComponents.blue, fraction: fraction),
                                     alpha: lerp(a: startColorComponents.alpha, b: endColorComponents.alpha, fraction: fraction))
            (node as? SKSpriteNode)?.color = transColor
        }
        )
    }
}

Usage:

redSKSpriteNodeThatBecomesBlue.run(SKAction.colorTransitionAction(fromColor: .red, toColor: .blue, duration: 5))

Please note that for SKShapeNode or other purposes you need to rewrite this line to suit your need:

(node as? SKSpriteNode)?.color = transColor

This solution is heavily inspired originally by Paddy Collins answer.

Answer 2

Use customActionWithDuration:block: and change the fillColor or strokeColor properties.

I suppose the colorize actions won't work because SKShapeNode has no color property. It's worth a try to add this property to the class in a subclass or category and redirect it to fillColor or strokeColor or both.

Answer 3

Here is my implementation. I think a little easier to read.

-(SKAction*)getColorFadeActionFrom:(SKColor*)col1 toColor:(SKColor*)col2 {

    // get the Color components of col1 and col2
    CGFloat r1 = 0.0, g1 = 0.0, b1 = 0.0, a1 =0.0;
    CGFloat r2 = 0.0, g2 = 0.0, b2 = 0.0, a2 =0.0;
    [col1 getRed:&r1 green:&g1 blue:&b1 alpha:&a1];
    [col2 getRed:&r2 green:&g2 blue:&b2 alpha:&a2];

    // return a color fading on the fill color
    CGFloat timeToRun = 0.3;

    return [SKAction customActionWithDuration:timeToRun actionBlock:^(SKNode *node, CGFloat elapsedTime) {

        CGFloat fraction = elapsedTime / timeToRun;

        SKColor *col3 = [SKColor colorWithRed:lerp(r1,r2,fraction)
                                        green:lerp(g1,g2,fraction)
                                         blue:lerp(b1,b2,fraction)
                                        alpha:lerp(a1,a2,fraction)];

        [(SKShapeNode*)node setFillColor:col3];
        [(SKShapeNode*)node setStrokeColor:col3];
    }];
}

double lerp(double a, double b, double fraction) {
    return (b-a)*fraction + a;
}

Answer 4

I wanted a continuous throbbing glow on my polygon. I used runBlock: instead of customActionWithDuration:block: but could have just run infinitely with that one.

SKShapeNode *shape = [SKShapeNode shapeNodeWithPoints:points count:indices.count];
shape.fillColor = [[SKColor yellowColor] colorWithAlphaComponent:0.2];
shape.strokeColor = [SKColor clearColor];
[self addChild:shape];
shape.userData = @{@"minAlpha": @0, @"maxAlpha": @0.5, @"deltaAlpha": @.025}.mutableCopy;
SKAction *a = [SKAction runBlock:^{
  SKColor *color = shape.fillColor;
  CGFloat delta = [shape.userData[@"deltaAlpha"] floatValue];
  CGFloat w, alpha; [color getWhite:&w alpha:&alpha];
  shape.fillColor = [color colorWithAlphaComponent:alpha + delta];
  if ((delta < 0 && alpha <= [shape.userData[@"minAlpha"] floatValue]) ||
      (delta > 0 && alpha >= [shape.userData[@"maxAlpha"] floatValue])) {
    shape.userData[@"deltaAlpha"] = @(-delta);
  }
}];
SKAction *slice = [SKAction sequence:@[a, [SKAction waitForDuration:0.05]]];
SKAction *glow = [SKAction repeatActionForever:slice];
[shape runAction:glow];

Answer 5

Adding to mogelbuster's answer, which is adding to GOR's answer, which is adding to Patrick Collins' answer.

Swift 4

func shapeColorChangeAction(from fromColor: UIColor, to toColor: UIColor, withDuration duration: TimeInterval) -> SKAction {

    func components(for color: UIColor) -> [CGFloat] {
        var comp = color.cgColor.components!
        // converts [white, alpha] to [red, green, blue, alpha]
        if comp.count < 4 {
            comp.insert(comp[0], at: 0)
            comp.insert(comp[0], at: 0)
        }
        return comp
    }
    func lerp(a: CGFloat, b: CGFloat, fraction: CGFloat) -> CGFloat {
        return (b-a) * fraction + a
    }

    let fromComp = components(for: fromColor)
    let toComp = components(for: toColor)
    let durationCGFloat = CGFloat(duration)
    return SKAction.customAction(withDuration: duration, actionBlock: { (node, elapsedTime) -> Void in
        let fraction = elapsedTime / durationCGFloat
        let transColor = UIColor(red: lerp(a: fromComp[0], b: toComp[0], fraction: fraction),
                                 green: lerp(a: fromComp[1], b: toComp[1], fraction: fraction),
                                 blue: lerp(a: fromComp[2], b: toComp[2], fraction: fraction),
                                 alpha: lerp(a: fromComp[3], b: toComp[3], fraction: fraction))
        (node as! SKShapeNode).fillColor = transColor
    })
}

Answer 6

I found GOR's answer above helpful, who found Paddy Collin's answer above helpful, so I extended it to animate through an array of colors.

extension SKAction {

func multipleColorTransitionAction(colors:[SKColor], duration:Double) -> SKAction {
    guard colors.count > 1 else { return SKAction.colorize(withColorBlendFactor: 1, duration: 0) }
    var colorActions:[SKAction] = []
    for i in 1..<colors.count {
        colorActions.append( colorTransitionAction(fromColor: colors[i-1] , toColor: colors[i], duration: duration/Double(colors.count)) )
    }
    colorActions.append(colorTransitionAction(fromColor: colors.last!, toColor: colors.first!, duration: duration/Double(colors.count)))
    return SKAction.sequence(colorActions)
}

func colorTransitionAction(fromColor : SKColor, toColor : SKColor, duration : Double = 0.4) -> SKAction {
    func lerp(_ a : CGFloat, b : CGFloat, fraction : CGFloat) -> CGFloat { return (b-a) * fraction + a }
    var frgba:[CGFloat] = [0,0,0,0]
    var trgba:[CGFloat] = [0,0,0,0]
    fromColor.getRed(&frgba[0], green: &frgba[1], blue: &frgba[2], alpha: &frgba[3])
    toColor.getRed(&trgba[0], green: &trgba[1], blue: &trgba[2], alpha: &trgba[3])

    return SKAction.customAction(withDuration: duration, actionBlock: { (node : SKNode!, elapsedTime : CGFloat) -> Void in
        let fraction = CGFloat(elapsedTime / CGFloat(duration))
        let transColor = UIColor(red:   lerp(frgba[0], b: trgba[0], fraction: fraction),
                                 green: lerp(frgba[1], b: trgba[1], fraction: fraction),
                                 blue:  lerp(frgba[2], b: trgba[2], fraction: fraction),
                                 alpha: lerp(frgba[3], b: trgba[3], fraction: fraction))
        (node as! SKShapeNode).fillColor = transColor
    })
}
}

I changed a few things about GOR's original function to accommodate for multiple colors, mainly encapsulating frgba, trgba, and lerp so the block doesn't need a reference to self, and to allow frgba and trgba to have multiple instances captured by multiple blocks. Here is an example usage:

let theRainbow:[SKColor] = [.red,.orange,.yellow,.green,.cyan,.blue,.purple,.magenta]
let rainbowSequenceAction = SKAction.multipleColorTransitionAction(colors: theRainbow, duration: 10)
star.run(SKAction.repeatForever(rainbowSequenceAction))

Where star is an SKShapeNode.