Swift: make rotation of point in 2D - ios

Question

I want to make a rotation of point by -90 degrees
Initial
Final
Let's take a look on top left and top right points of Initial. Their coordinates are:
let topLeft = CGPoint(x: 2, y: 1)
let topRight = CGPoint(x: 3, y: 1)
And after rotation coordinates of them should become:
topLeft 1:0
topRight 2:0
How can i do it ?
I have tried several answers but none of them give me my final results.
did not work:
Rotating a CGPoint around another CGPoint
What is the best way to rotate a CGPoint on a grid?
Here are some code from my playground:
let topLeft = CGPoint(x: 2, y: 1)
let topRight = CGPoint(x: 3, y: 1)
func rotatePoint1(_ point: CGPoint, _ degrees: CGFloat) -> CGPoint {
let s = CGFloat(sinf(Float(degrees)))
let c = CGFloat(cosf(Float(degrees)));
return CGPoint(x: c * point.x - s * point.y, y: s * point.x + c * point.y)
}
func rotatePoint2(_ point: CGPoint, _ degrees: CGFloat, _ origin: CGPoint) -> CGPoint {
let dx = point.x - origin.x
let dy = point.y - origin.y
let radius = sqrt(dx * dx + dy * dy)
let azimuth = atan2(dy, dx) // in radians
let newAzimuth = azimuth + degrees * CGFloat(M_PI / 180.0) // convert it to radians
let x = origin.x + radius * cos(newAzimuth)
let y = origin.y + radius * sin(newAzimuth)
return CGPoint(x: x, y: y)
}
func rotatePoint3(_ point: CGPoint, _ degrees: CGFloat) -> CGPoint {
let translateTransform = CGAffineTransform(translationX: point.x, y: point.y)
let rotationTransform = CGAffineTransform(rotationAngle: degrees)
let customRotation = (rotationTransform.concatenating(translateTransform.inverted())).concatenating(translateTransform)
return point.applying(customRotation)
}
print(rotatePoint1(topLeft, -90))
print(rotatePoint1(topRight, -90))

Answer 1

You are really describing two rotations with your example:
The points are rotated by -90 degrees around the center of the 3x3 grid. When this happens, the topLeft point becomes bottomLeft, and topRight becomes topLeft.
Then you rotate those points around the center of the square 90 degrees (ie. the other direction) to make them topLeft and topRight again.
Using this function from this answer:
func rotatePoint(target: CGPoint, aroundOrigin origin: CGPoint, byDegrees: CGFloat) -> CGPoint {
let dx = target.x - origin.x
let dy = target.y - origin.y
let radius = sqrt(dx * dx + dy * dy)
let azimuth = atan2(dy, dx) // in radians
let newAzimuth = azimuth + byDegrees * .pi / 180 // convert it to radians
let x = origin.x + radius * cos(newAzimuth)
let y = origin.y + radius * sin(newAzimuth)
return CGPoint(x: x, y: y)
}
let topLeft = CGPoint(x: 2, y: 1)
let topRight = CGPoint(x: 3, y: 1)
let squareCenter = CGPoint(x: 2.5, y: 1.5)
// First rotate around the center of the 3 x 3 square
let centerOfRotation = CGPoint(x: 1.5, y: 1.5)
let tl1 = rotatePoint(target: topLeft, aroundOrigin: centerOfRotation, byDegrees: -90) // (x 1 y 1)
let tr1 = rotatePoint(target: topRight, aroundOrigin: centerOfRotation, byDegrees: -90) // (x 1 y 0)
let sc1 = rotatePoint(target: squareCenter, aroundOrigin: centerOfRotation, byDegrees: -90) // (x 1.5 y 0.5)
// Now rotate the 1x1 square the other way around new position of square center
let tl2 = rotatePoint(target: tl1, aroundOrigin: sc1, byDegrees: 90) // (x 1 y 0)
let tr2 = rotatePoint(target: tr1, aroundOrigin: sc1, byDegrees: 90) // (x 2 y 0)
Note: As #MBo noted in the comments, if your cell is always 1x1, it is sufficient to rotate the center of your cell and then just add and subtract the 0.5 offsets to find the four corners.

Answer 2

You can just transform you view like so
yourView.transform = CGAffineTransform(rotationAngle: -CGFloat.pi/2)
EDIT:
My bad.
Use CGFloat.pi when working with degrees
print(rotatePoint1(topLeft, -CGFloat.pi/2))
Use sin and cos functions directly
let s = sin(degrees)
let c = cos(degrees)
iOS coordinate system is a bit flipped compared to standard one so you will have to adjust the angle (you can see simulation)
print(rotatePoint1(topLeft, -CGFloat.pi/2)) // (1.0000000000000002, -2.0)
print(rotatePoint1(topRight, -CGFloat.pi/2)) // (1.0000000000000002, -3.0)