我有一个图像，可以响应捏合，旋转和平移手势。我希望图像的捏合和旋转将相对于放置在屏幕中间的锚点完成，就像使用Xcode iPhone模拟器按下选项键一样。如果图像的中心可以缩放并平移到不同的位置，如何将锚点放在屏幕中间？
这是我的缩放和旋转手势功能：
@IBAction func pinchGesture(_ gestureRecognizer: UIPinchGestureRecognizer) {
// Move the achor point of the view's layer to the touch point
// so that scaling the view and the layer becames simpler.
self.adjustAnchorPoint(gestureRecognizer: gestureRecognizer)
// Scale the view by the current scale factor.
if(gestureRecognizer.state == .began) {
// Reset the last scale, necessary if there are multiple objects with different scales
lastScale = gestureRecognizer.scale
}
if (gestureRecognizer.state == .began || gestureRecognizer.state == .changed) {
let currentScale = gestureRecognizer.view!.layer.value(forKeyPath:"transform.scale")! as! CGFloat
// Constants to adjust the max/min values of zoom
let kMaxScale:CGFloat = 15.0
let kMinScale:CGFloat = 1.0
var newScale = 1 - (lastScale - gestureRecognizer.scale)
newScale = min(newScale, kMaxScale / currentScale)
newScale = max(newScale, kMinScale / currentScale)
let transform = (gestureRecognizer.view?.transform)!.scaledBy(x: newScale, y: newScale);
gestureRecognizer.view?.transform = transform
lastScale = gestureRecognizer.scale // Store the previous scale factor for the next pinch gesture call
scale = currentScale // Save current scale for later use
}
}
@IBAction func rotationGesture(_ gestureRecognizer: UIRotationGestureRecognizer) {
// Move the achor point of the view's layer to the center of the
// user's two fingers. This creates a more natural looking rotation.
self.adjustAnchorPoint(gestureRecognizer: gestureRecognizer)
// Apply the rotation to the view's transform.
if gestureRecognizer.state == .began || gestureRecognizer.state == .changed {
gestureRecognizer.view?.transform = (gestureRecognizer.view?.transform.rotated(by: gestureRecognizer.rotation))!
// Set the rotation to 0 to avoid compouding the
// rotation in the view's transform.
angle += gestureRecognizer.rotation // Save rotation angle for later use
gestureRecognizer.rotation = 0.0
}
}
func adjustAnchorPoint(gestureRecognizer : UIGestureRecognizer) {
if gestureRecognizer.state == .began {
let view = gestureRecognizer.view
let locationInView = gestureRecognizer.location(in: view)
let locationInSuperview = gestureRecognizer.location(in: view?.superview)
// Move the anchor point to the the touch point and change the position of the view
view?.layer.anchorPoint = CGPoint(x: (locationInView.x / (view?.bounds.size.width)!), y: (locationInView.y / (view?.bounds.size.height)!))
view?.center = locationInSuperview
}
}
修改
我看到人们并不急于进入这个领域。让我帮助分享我过去几天取得的一些进展。
首先，我写了一个函数centerAnchorPoint，它正确地将图像的锚点放在屏幕的中心，而不管之前的锚点在哪里。但是，不得缩放或旋转图像以使其工作。
func setAnchorPoint(_ anchorPoint: CGPoint, forView view: UIView) {
var newPoint = CGPoint(x: view.bounds.size.width * anchorPoint.x, y: view.bounds.size.height * anchorPoint.y)
var oldPoint = CGPoint(x: view.bounds.size.width * view.layer.anchorPoint.x, y: view.bounds.size.height * view.layer.anchorPoint.y)
newPoint = newPoint.applying(view.transform)
oldPoint = oldPoint.applying(view.transform)
var position = view.layer.position
position.x -= oldPoint.x
position.x += newPoint.x
position.y -= oldPoint.y
position.y += newPoint.y
view.layer.position = position
view.layer.anchorPoint = anchorPoint
}
func centerAnchorPoint(gestureRecognizer : UIGestureRecognizer) {
if gestureRecognizer.state == .ended {
view?.layer.anchorPoint = CGPoint(x: (photo.bounds.midX / (view?.bounds.size.width)!), y: (photo.bounds.midY / (view?.bounds.size.height)!))
}
}
func centerAnchorPoint() {
// Position of the current anchor point
let currentPosition = photo.layer.anchorPoint
self.setAnchorPoint(CGPoint(x: 0.5, y: 0.5), forView: photo)
// Center of the image
let imageCenter = CGPoint(x: photo.center.x, y: photo.center.y)
self.setAnchorPoint(currentPosition, forView: photo)
// Center of the screen
let screenCenter = CGPoint(x: UIScreen.main.bounds.midX, y: UIScreen.main.bounds.midY)
// Distance between the centers
let distanceX = screenCenter.x - imageCenter.x
let distanceY = screenCenter.y - imageCenter.y
// Find new anchor point
let newAnchorPoint = CGPoint(x: (imageCenter.x+2*distanceX)/(UIScreen.main.bounds.size.width), y: (imageCenter.y+2*distanceY)/(UIScreen.main.bounds.size.height))
//photo.layer.anchorPoint = newAnchorPoint
self.setAnchorPoint(newAnchorPoint, forView: photo)
let dotPath = UIBezierPath(ovalIn: CGRect(x: photo.layer.position.x-2.5, y: photo.layer.position.y-2.5, width: 5, height: 5))
layer.path = dotPath.cgPath
}
此处使用函数setAchorPoint将锚点设置为新位置而不移动图像。
然后我通过在其末尾插入来更新panGesture函数：
if gestureRecognizer.state == .ended {
self.centerAnchorPoint()
}
编辑2
好的，我会尝试简单解释上面的代码。
我在做的是：
newAnchorPointX =（imageCenter.x-distanceX）/ screenWidth + distanceX / screenWidth
然后为y位置做同样的事情。
setAnchorPoint函数正如我所说，如果图像没有缩放，这种方法很有效。如果是，则锚点不会停留在中心位置。
奇怪的是，距离X或距离Y并不完全取决于比例值，所以这样的事情并不是很有效：
newAnchorPointX =（imageCenter.x-distanceX）/ screenWidth + distanceX /（scaleValue * screenWidth）
编辑3
我想出了缩放比例。似乎正确的比例因子必须是：
scaleFactor = photo.frame.size.width/photo.layer.bounds.size.width
我使用了这个而不是scaleValue，而且效果非常好。
完成平移和缩放。唯一剩下的就是轮换，但看起来它是最难的。
我首先想到的是将旋转矩阵应用于X和Y方向的增量，如下所示：
let incrementX = (distanceX)/(screenWidth)
let incrementY = (distanceY)/(screenHeight)
// Applying rotation matrix
let incX = incrementX*cos(angle)+incrementY*sin(angle)
let incY = -incrementX*sin(angle)+incrementY*cos(angle)
// Find new anchor point
let newAnchorPoint = CGPoint(x: 0.5+incX, y: 0.5+incY)
然而，这不起作用。
答案 0 :(得分：1)
由于这个问题主要是在编辑中回答的，所以我不想过多地重复自己。
大致上我从原始问题中发布的代码中改变了：
adjustAnchorPoint功能的调用。 将这段代码放在平移手势功能中，以便在平移照片后锚点会更新其位置：
如果gestureRecognizer.state == .ended { self.centerAnchorPoint（） }
更新centerAnchorPoint功能以便轮换。
完全正常的centerAnchorPoint功能（包括旋转）：
func centerAnchorPoint() {
// Scale factor
photo.transform = photo.transform.rotated(by: -angle)
let curScale = photo.frame.size.width / photo.layer.bounds.size.width
photo.transform = photo.transform.rotated(by: angle)
// Position of the current anchor point
let currentPosition = photo.layer.anchorPoint
self.setAnchorPoint(CGPoint(x: 0.5, y: 0.5), forView: photo)
// Center of the image
let imageCenter = CGPoint(x: photo.center.x, y: photo.center.y)
self.setAnchorPoint(currentPosition, forView: photo)
// Center of the screen
let screenCenter = CGPoint(x: UIScreen.main.bounds.midX, y: UIScreen.main.bounds.midY)
// Distance between the centers
let distanceX = screenCenter.x - imageCenter.x
let distanceY = screenCenter.y - imageCenter.y
// Apply rotational matrix to the distances
let distX = distanceX*cos(angle)+distanceY*sin(angle)
let distY = -distanceX*sin(angle)+distanceY*cos(angle)
let incrementX = (distX)/(curScale*UIScreen.main.bounds.size.width)
let incrementY = (distY)/(curScale*UIScreen.main.bounds.size.height)
// Find new anchor point
let newAnchorPoint = CGPoint(x: 0.5+incrementX, y: 0.5+incrementY)
self.setAnchorPoint(newAnchorPoint, forView: photo)
}
这里需要注意的关键是旋转矩阵必须应用于distanceX和distanceY。比例因子也会更新，以便在整个轮换期间保持不变。