Andy Fedoroff Andy Fedoroff - 1 year ago 111
Swift Question

How to simultaneously move four rectangle's points?

I'm writing a code for app building rectangles. I can separately move rectangles' points with mouse.

How could I move all four points of a rectangle simultaneously?

The principle of operation: if I drag 1 point with a mouse, the other 3 will follow it at the same time with the same offset.

enter image description here

This is how elements were constructed:

enum RectPoint {

case point1(point: CGPoint)
case point2(point: CGPoint)
case point3(point: CGPoint)
case point4(point: CGPoint)

func pointCoord() -> [CGPoint] {
switch self {
case .point1(let point): return [point]
case .point2(let point): return [point]
case .point3(let point): return [point]
case .point4(let point): return [point]

class SpecialView: NSView {

var array: [RectPoint] = []
private var trackVertex: RectPoint?
private var trackVertexIndex: Int?
private var trackElementIndex: Int?


private func updateDragging(point: CGPoint) {
guard let trackVertex = self.trackVertex,
let trackVertexIndex = self.trackVertexIndex,
let trackElementIndex = self.trackElementIndex
else {

let newVertex = trackVertex.debugReleaseChecking(point,
atElementIndex: trackElementIndex)

array[trackVertexIndex] = newVertex
self.needsDisplay = true

Here's a method for dragging with LMB:

func mouseDragged(event: NSEvent) {

var point = self.convertPoint(event.locationInWindow, fromView: nil)


I need a code (or pseudo code) that allows me to drag all four points of any rectangle at a time.

Answer Source

Basically, you need to calculate the offset that is being applied to the tracked point and apply that offset to all the other points. It's easiest to do this by separating the calculation and the update, so the update always runs on all points.

To calculate the offset just subtract the current point x and y from the new point x and y.

Something along the lines of:

func mouseDragged(event: NSEvent) {
    let eventPoint = self.convertPoint(event.locationInWindow, fromView: nil)
    let trackingPoint = XXX

    let xOffset = eventPoint.x - trackingPoint.x
    let yOffset = eventPoint.y - trackingPoint.y

    for point in allPoints {
        point.x += xOffset
        point.y += yOffset
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