SpriteKit 中的正弦波运动 [英] Sine Wave Motion In SpriteKit

问题描述

我想从屏幕中的第一个点到屏幕中的最后一个点进行正弦波运动，与屏幕大小无关.

I want to make sine wave motion from the first point in the screen to the last Point in the screen, independent on the size of the screen.

这是我的代码，但它不能正常工作:

Here is my code, but it doesn't work correctly:

 SKSpriteNode* RedBird = (SKSpriteNode*)[self childNodeWithName:@"RedBird"];
CGPoint currentPoint=CGPointMake(-60,0);
double width=self.frame.size.width/4;
CGPoint cp1=CGPointMake(width, self.frame.size.height/2);
CGPoint cp2=CGPointMake((width*3), 0);
CGPoint e=CGPointMake(self.frame.size.width+200, 0);


CGMutablePathRef cgpath = CGPathCreateMutable();


CGPathMoveToPoint(cgpath,NULL, currentPoint.x, currentPoint.y);
CGPathAddCurveToPoint(cgpath, NULL, cp1.x, cp1.y, cp2.x, cp2.y, e.x, e.y);



[RedBird runAction:[SKAction group:@[[SKAction repeatActionForever:RedBirdAnimation],[SKAction followPath:cgpath asOffset:YES orientToPath:NO duration:12.0]]]];


CGPathRelease(cgpath);

推荐答案

我同意@Gord，因为我认为 SKAction 是最好的方法.但是，当您可以使用 sin 函数时，无需逼近正弦曲线.

I agree with @Gord, in that I think SKActions are the best way to go. However, there is no need to approximate the sine curve when you can use the sin function.

首先，您需要 π，因为它对计算很有用:

Firstly, you need π as it's going to be useful for the calculations:

// Defined at global scope.
let π = CGFloat(M_PI)

其次，扩展 SKAction(在 Objective-C 中，这将通过类别完成)以轻松创建一个振荡相关节点的 SKAction:

Secondly, extend SKAction (in Objective-C this would be done with categories) to easily create an SKAction that oscillates the node in question:

extension SKAction {
    static func oscillation(amplitude a: CGFloat, timePeriod t: CGFloat, midPoint: CGPoint) -> SKAction {
        let action = SKAction.customActionWithDuration(Double(t)) { node, currentTime in
            let displacement = a * sin(2 * π * currentTime / t)
            node.position.y = midPoint.y + displacement
        }

        return action
    }
}

在上面的代码中:amplitude是振荡的高度；timePeriod 是一个完整周期的时间，midPoint 是发生振荡的点.displacement 的公式来自 Simple Harmonic Motion.

In the code above: amplitude is the height of the oscillation; timePeriod is the time for one complete cycle and the midPoint is the point around which the oscillation occurs. The formula for displacement comes from the equations for Simple Harmonic Motion.

第三，将所有内容放在一起.您可以结合 SKAction.oscillation 动作和 SKAction.moveByX 使精灵沿着曲线的路径移动.

Thirdly, putting that all together. You can combine the SKAction.oscillation action and SKAction.moveByX to make the sprite move along the path of the curve.

class GameScene: SKScene {
    override func didMoveToView(view: SKView) {
        let node = SKSpriteNode(color: UIColor.greenColor(), size: CGSize(width: 50, height: 50))
        node.position = CGPoint(x: 25, y: size.height / 2)
        self.addChild(node)

        let oscillate = SKAction.oscillation(amplitude: 200, timePeriod: 1, midPoint: node.position)
        node.runAction(SKAction.repeatActionForever(oscillate))
        node.runAction(SKAction.moveByX(size.width, y: 0, duration: 5))
    }
}

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