Question

我希望在我的游戏中有一些声波绕过屏幕。我能够制作一个直线的正弦但我如何将正弦旋转20度？例如，从左下角到右上角？

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Answer 1

您可以使用2 Bézier curves非常准确地使UIBezierPath近似正弦波：

/// Make a path that approximates a peak-to-peak sine wave
func sinePath(size: CGSize) -> UIBezierPath {
  let path = UIBezierPath()

  // path starts at 0,0
  path.move(to: CGPoint.zero)

  let halfWidth = size.width / 2.0

  // base x-values for control points
  // baseX approximates the best fit Bézier curve for a sine wave
  let baseX:  = CGFloat(0.3642124232)
  let firstX  = halfWidth * baseX
  let secondX = halfWidth * (1.0 - baseX)

  // curve from start peak to trough
  path.addCurve(to: CGPoint(x: halfWidth, y: size.height),
                controlPoint1: CGPoint(x: firstX , y: 0),
                controlPoint2: CGPoint(x: secondX, y: size.height))

  // curve from trough to end peak
  path.addCurve(to: CGPoint(x: size.width, y:0),
                controlPoint1: CGPoint(x: size.width - secondX, y: size.height),
                controlPoint2: CGPoint(x: size.width - firstX , y: 0))
  return path
}

然后你可以用这样的CGAffineTransform旋转它：

/// Convert degrees to radians
func degreeToRadian(_ angle: CGFloat) -> CGFloat {
  return angle * CGFloat.pi / 180.0
}

let path = sinePath(size: CGSize(width: 200.0, height: 100.0))
path.apply(CGAffineTransform(rotationAngle: degreeToRadian(20)))

我从这个问题得到baseX常数：

How to approximate a half-cosine curve with bezier paths in SVG?

Answer 2

您可以将旋转的仿射变换应用于计算的点位置

xnew = xbase + (x - xbase) * Cos(rot_angle) - (y - ybase) * Sin(rot_angle)
ynew = ybase + (x - xbase) * Sin(rot_angle) + (y - ybase) * Cos(rot_angle)

此处(xbase, ybase) - 旋转中心的坐标（在您的情况下可能是0,0），rot_angle - 旋转角度，在您的情况下20 * Pi / 180

可能你的图形库已经包含了仿射变换的工具，在这种情况下只是形成变换矩阵并应用它。

如何在spritekit swift中制作一个以角度旋转的正弦？

2 个答案: