How to find the distance between two CG points?

Question

When we do multitouch with two fingers in a UIScrollView, we get two CG points. I want to find the distance between them. Then when again we do the pinch(inside or outside), Then we will again get two points. Then after finding the distance again between these two points , I want to decide whether I pinched in or out. If i have pinched in, surely the new distance will be lesser and vice versa.

But don't know how to find an accurate measurement for the distance between 2 points for doing comparison ? Is anyone having idea about this ?

See [my answer for Swift 4](https://stackoverflow.com/a/46036132/1966109) that shows up to 5 different ways to find the distance between two `CGPoint`s. — Imanou Petit, Nov 18 '18 at 10:47

score 195 · Answer 1 · answered Apr 13 '13 at 04:52

195

You can use the hypot() or hypotf() function to calculate the hypotenuse. Given two points p1 and p2:

CGFloat distance = hypotf(p1.x - p2.x, p1.y - p2.y);

And that's it.

answered Apr 13 '13 at 04:52

lucius

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if using swift it's distance = hypotf(Float(p1.x) - Float(p2.x), Float(p1.y) - Float(p2.y)) – nwales Mar 05 '15 at 22:46
6

you mean `let distance = hypotf(Float(p1.x - p2.x), Float(p1.y - p2.y))` – average Joe Apr 13 '15 at 13:01
6

you mean `let distance = hypot(p1.x - p2.x, p1.y - p2.y)` since Swift 2.1 – Cemen Dec 26 '15 at 14:55
1

This function is actually the reason why I searched this question. – kelin Oct 26 '18 at 20:28

Ole Begemann · Accepted Answer · 2018-09-02T10:26:32.400

131

Distance between p1 and p2:

CGFloat xDist = (p2.x - p1.x);
CGFloat yDist = (p2.y - p1.y);
CGFloat distance = sqrt(xDist * xDist + yDist * yDist);

Put in a function:

func distance(_ a: CGPoint, _ b: CGPoint) -> CGFloat {
    let xDist = a.x - b.x
    let yDist = a.y - b.y
    return CGFloat(sqrt(xDist * xDist + yDist * yDist))
}

Background: Pythagorean theorem

If you only need to calculate if the distance between the points increases or decreases, you can omit the sqrt() which will make it a little faster.

edited Sep 02 '18 at 10:26

answered Dec 15 '09 at 10:57

Ole Begemann

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Is there no convenience method for this? – SpacyRicochet Oct 11 '12 at 12:17
23

Computational geometry axiom #1: if you are *comparing* distances, there is no need to incur the cost of the sqrt() operation. – QED Apr 13 '13 at 05:01
4

@SpaceyRicochet there are methods hypotf and ccpDistance. See answers below. – rmp251 Mar 05 '14 at 23:08
@QED Does the value before you take the square root have a name or significance beyond an intermediate step of calculating the distance? – allenh Oct 20 '17 at 21:11
@AllenHumphreys nothing I know of more poetic than *distance squared*. – QED Oct 22 '17 at 01:12

score 32 · Answer 3 · edited Jul 31 '19 at 07:10

32

For swift users

extension CGPoint {
    func distance(to point: CGPoint) -> CGFloat {
        return sqrt(pow(x - point.x, 2) + pow(y - point.y, 2))
    }
}

edited Jul 31 '19 at 07:10

Leo

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answered Jul 08 '15 at 13:15

Daniel Krom

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score 19 · Answer 4 · answered Sep 04 '17 at 11:33

With Swift 4, you may choose one of the 5 following Playground codes in order to get the distance between two CGPoint instances.

1. Using Darwin `sqrt(_:)` function

import CoreGraphics

func distance(from lhs: CGPoint, to rhs: CGPoint) -> CGFloat {
    let xDistance = lhs.x - rhs.x
    let yDistance = lhs.y - rhs.y
    return sqrt(xDistance * xDistance + yDistance * yDistance)
}

let point1 = CGPoint(x: -10, y: -100)
let point2 = CGPoint(x: 30, y: 600)

distance(from: point1, to: point2) // 701.141925718324

2. Using `CGFloat` `squareRoot()` method

import CoreGraphics

func distance(from lhs: CGPoint, to rhs: CGPoint) -> CGFloat {
    let xDistance = lhs.x - rhs.x
    let yDistance = lhs.y - rhs.y
    return (xDistance * xDistance + yDistance * yDistance).squareRoot()
}

let point1 = CGPoint(x: -10, y: -100)
let point2 = CGPoint(x: 30, y: 600)

distance(from: point1, to: point2) // 701.141925718324

3. Using `CGFloat` `squareRoot()` method and Core Graphics `pow(_:_:)` function

import CoreGraphics

func distance(from lhs: CGPoint, to rhs: CGPoint) -> CGFloat {
    return (pow(lhs.x - rhs.x, 2) + pow(lhs.y - rhs.y, 2)).squareRoot()
}

let point1 = CGPoint(x: -10, y: -100)
let point2 = CGPoint(x: 30, y: 600)

distance(from: point1, to: point2) // 701.141925718324

4. Using Core Graphics `hypot(_:_:)` function

import CoreGraphics

func distance(from lhs: CGPoint, to rhs: CGPoint) -> CGFloat {
    return hypot(lhs.x - rhs.x, lhs.y - rhs.y)
}

let point1 = CGPoint(x: -10, y: -100)
let point2 = CGPoint(x: 30, y: 600)

distance(from: point1, to: point2) // 701.141925718324

5. Using Core Graphics `hypot(_:_:)` function and `CGFloat` `distance(to:)` method

import CoreGraphics

func distance(from lhs: CGPoint, to rhs: CGPoint) -> CGFloat {
    return hypot(lhs.x.distance(to: rhs.x), lhs.y.distance(to: rhs.y))
}

let point1 = CGPoint(x: -10, y: -100)
let point2 = CGPoint(x: 30, y: 600)

distance(from: point1, to: point2) // 701.141925718324

haawa · Answer 5 · 2013-04-09T20:08:03.657

12

-(float)distanceFrom:(CGPoint)point1 to:(CGPoint)point2
{
CGFloat xDist = (point2.x - point1.x);
CGFloat yDist = (point2.y - point1.y);
return sqrt((xDist * xDist) + (yDist * yDist));
}

If you are using cocos2d

float distance = ccpDistance(point1, point2);

edited Apr 09 '13 at 20:08

answered Dec 20 '12 at 16:55

haawa

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It appears ccpDistance is part of cocos2d, not part of core. Including it to avoid the pythagorean theorem is probably overkill. – Vox Feb 21 '13 at 20:34

score 3 · Answer 6 · edited Jul 09 '13 at 07:30

3

I wrote this, I use it a lot:

- (float) distanceBetween : (CGPoint) p1 and: (CGPoint) p2
{
    return sqrt(pow(p2.x-p1.x,2)+pow(p2.y-p1.y,2));
}

Call like this:

float distanceMoved = [self distanceBetween touchStart and: touchEnd];

I normally use cocos2d, but I still use my own function for some things because when I was learning I wrote a bunch of my own functions for simple stuff rather than searching for the "official" higher order functions, and additionally I'm not a big fan of functions(vars, vars), I prefer [self functions vars and: vars]

edited Jul 09 '13 at 07:30

Oded Ben Dov

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answered Jun 14 '13 at 11:46

redux

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shouldn't it be sqrt(pow(p2.x-p1.x,2)+pow(p2.y-p1.y,2))? second occurrence of p2.y replaced p1.y. – Sanjay Chaudhry Jul 05 '13 at 18:46

score 0 · Answer 7 · edited Mar 21 '14 at 15:49

0

If you want to find the absolute distance value between two points then you can use (for Cocos2d):

float distance = abs(ccpDistance(point1, point2));

edited Mar 21 '14 at 15:49

Chris

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answered May 27 '13 at 13:21

user2425159

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score 0 · Answer 8 · answered Jul 28 '13 at 14:08

#define rw_pointOffset(point1, point2) CGPointMake(point2.x - point1.x, point2.y - point1.y)
#define rw_pointDistance(point1, point2) sqrtf( powf(point2.x - point1.x, 2.0f) + powf(point2.y - point1.y, 2.0f))

And that´s how you use it:

CGPoint offset = rw_pointOffset(view1.center, view2.center);
float distance = rw_pointDistance(view1.center, view2.center);

How to find the distance between two CG points?

8 Answers8

1. Using Darwin `sqrt(_:)` function

2. Using `CGFloat` `squareRoot()` method

3. Using `CGFloat` `squareRoot()` method and Core Graphics `pow(_:_:)` function

4. Using Core Graphics `hypot(_:_:)` function

5. Using Core Graphics `hypot(_:_:)` function and `CGFloat` `distance(to:)` method

Linked

How to find the distance between two CG points?

8 Answers8

1. Using Darwin sqrt(_:) function

2. Using CGFloat squareRoot() method

3. Using CGFloat squareRoot() method and Core Graphics pow(_:_:) function

4. Using Core Graphics hypot(_:_:) function

5. Using Core Graphics hypot(_:_:) function and CGFloat distance(to:) method

Linked

1. Using Darwin `sqrt(_:)` function

2. Using `CGFloat` `squareRoot()` method

3. Using `CGFloat` `squareRoot()` method and Core Graphics `pow(_:_:)` function

4. Using Core Graphics `hypot(_:_:)` function

5. Using Core Graphics `hypot(_:_:)` function and `CGFloat` `distance(to:)` method