How to get all Points Along a Line in Swift? - ios

Question

I am writing a program in Swift which requires a method that uses specification of two CGPoints and returns all points in a straight line in-between them. At the moment I am trialling the following method, but it is very glitchy and refuses to get all points for some lines. I was just wondering if there is a more efficient way of doing this?
func addPointsInLine(#start: CGPoint, end: CGPoint){
var speed = 0
var startNo = trackPoints.count
var endNo = startNo
var xDiff = start.x - end.x
var yDiff = start.y - end.y
var xChange = 0.0
var yChange = 0.0
var newPointX = start.x
var newPointY = start.y
var ended = false
xChange = Double(xDiff) / Double(yDiff)
yChange = Double(yDiff) / Double(xDiff)
/*if(xDiff > 0){
xChange = sqrt(xChange * xChange)
}
if(yDiff > 0){
yChange = sqrt(yChange * yChange)
}*/
println("xc \(xChange)")
println("yc \(yChange)")
var y = Double(start.y)
var x = Double(start.x)
while !ended {
println(trackPoints.count)
speed++
endNo++
if(CGPointMake(newPointX, newPointY) == end){
ended = true
}
if(yChange > xChange){
y++
x += xChange
trackPoints.append(TrackPoint(x: Int(x), y: Int(y)))
if(CGFloat(Int(y)) == end.y){
ended = true
println("end")
//break
}
/* if(yChange > 0){
if(CGFloat(Int(y)) > end.y){
ended = true
println("end>y")
// break
}
}
if(yChange < 0){
if(CGFloat(Int(y)) < end.y){
ended = true
println("end<y")
//break
}
}*/
if(xChange > 0){
if(CGFloat(Int(x)) >= end.x){
ended = true
println("end>x")
//break
}
}
if(xChange < 0){
if(CGFloat(Int(x)) <= end.x){
ended = true
println("end<x")
//break
}
}
} else {
x++
y += yChange
trackPoints.append(TrackPoint(x: Int(x), y: Int(y)))
if(CGFloat(Int(x)) == end.x){
ended = true
println("end")
//break
}
/* if(xChange > 0){
if(CGFloat(Int(x)) >= end.x){
ended = true
println("end>x")
//break
}
}
if(xChange < 0){
if(CGFloat(Int(x)) <= end.x){
ended = true
println("end<x")
//break
}
}*/
if(yChange > 0){
if(CGFloat(Int(y)) > end.y){
ended = true
println("end>y")
// break
}
}
if(yChange < 0){
if(CGFloat(Int(y)) < end.y){
ended = true
println("end<y")
//break
}
}
}
}
println("finished")
var i = startNo
println(startNo)
println(endNo)
while i < endNo {
trackPoints[i].speed = speed
i++
}
println("finish2")
}

Answer 1

I think firstly finding all points isn't possible because there are infinite points in a straight line. Take example of line joining (0,0) to (1, 0). All the following points and many more are on the said line (0.00001,0) (0.0000000000001,0) (0.01,0)
So you need to limit the amount of points you need to find like all the points with Integer co-ordinates. All the points 1 unit apart, starting from starting point etc.
Next you can use one of equations of line to get points: Equations of Line

Answer 2

Try this,
func findAllPointsBetweenTwoPoints(startPoint : CGPoint, endPoint : CGPoint) {
var allPoints :[CGPoint] = [CGPoint]()
let deltaX = fabs(endPoint.x - startPoint.x)
let deltaY = fabs(endPoint.y - startPoint.y)
var x = startPoint.x
var y = startPoint.y
var err = deltaX-deltaY
var sx = -0.5
var sy = -0.5
if(startPoint.x<endPoint.x){
sx = 0.5
}
if(startPoint.y<endPoint.y){
sy = 0.5;
}
repeat {
let pointObj = CGPoint(x: x, y: y)
allPoints.append(pointObj)
let e = 2*err
if(e > -deltaY)
{
err -= deltaY
x += CGFloat(sx)
}
if(e < deltaX)
{
err += deltaX
y += CGFloat(sy)
}
} while (round(x) != round(endPoint.x) && round(y) != round(endPoint.y));
allPoints.append(endPoint)
}