CODEWITHSUNDEEP
iphoneobjective-ccocoa-touchcocoa
JWood
JWood

Reputation: 2834

Multiple CGPoints to CGRect

I have a a set of CGPoints which represent a shape which is a bit like an upside down 'T' shape, now I want to convert those points into a CGRect which fits inside the shape, so to create a CGRect which encompasses the entire shape I just loop through and work out the lowest x and y for the top left and the highest x and y for the bottom right which is great but leaves white areas outside of the image, how could I figure out the largest rectangle without white areas so the final shape is more like an '|' shape? My code so far:

CGPoint topLeft = CGPointZero;
CGPoint bottomRight = CGPointZero;
for( NSValue *value in points ) {
    CGPoint point = [value CGPointValue];
    if( topLeft.x == 0 || topLeft.x > point.x ) shapeRect.x = point.x;
    if( topLeft.y == 0 || topLeft.y > point.y ) shapeRect.y = point.y;
    if( bottomRight.x < point.x ) bottomRight.x = point.x;
    if( bottomRight.y < point.y ) bottomRight.y = point.y;
}
CGRect shapeRect = CGRectMake(topLeft.x, topLeft.y, bottomRight.x - topLeft.x, bottomRight.y - topLeft.y);

EDIT: I've drawn some pics to show what I'm trying to achieve. Grey areas show the CGRect.

Here's the image shape, I have coordinates for each point in the shape:

Image Hosted by ImageShack.us http://img684.imageshack.us/img684/121/crop1.png

Here's what my code above produces:

Image Hosted by ImageShack.us http://img26.imageshack.us/img26/2521/crop2j.png

Here's what I'm trying to achieve:

Image Hosted by ImageShack.us http://img689.imageshack.us/img689/5499/crop3.png

Upvotes: 3

Views: 3819

Answers (5)

OscarVGG
OscarVGG

Reputation: 2670

If you want, you can use Core Graphics:

let path = CGMutablePath()
path.addLines(between: [p1, p2, p3, p4])
return path.boundingBoxOfPath

Upvotes: 2

Chajmz
Chajmz

Reputation: 749

Swift version of hfossli (it works great !) : 

func pointToRect(pointsArray: [CGPoint]) -> CGRect {
    var greatestXValue = pointsArray[0].x
    var greatestYValue = pointsArray[0].y
    var smallestXValue = pointsArray[0].x
    var smallestYValue = pointsArray[0].y
    for point in pointsArray {
        greatestXValue = max(greatestXValue, point.x);
        greatestYValue = max(greatestYValue, point.y);
        smallestXValue = min(smallestXValue, point.x);
        smallestYValue = min(smallestYValue, point.y);
    }
    let origin = CGPoint(x: smallestXValue, y: smallestYValue)
    let size = CGSize(width: greatestXValue - smallestXValue, height: greatestYValue - smallestYValue)
    return CGRect(origin: origin, size: size)
}

Upvotes: 3

hfossli
hfossli

Reputation: 22972

Hard to get a grip on what you are actually asking about. In regards to the title this function will create the smallest rect for any number of CGPoints.

CGRect CGRectSmallestWithCGPoints(CGPoint pointsArray[], int numberOfPoints)
{
    CGFloat greatestXValue = pointsArray[0].x;
    CGFloat greatestYValue = pointsArray[0].y;
    CGFloat smallestXValue = pointsArray[0].x;
    CGFloat smallestYValue = pointsArray[0].y;

    for(int i = 1; i < numberOfPoints; i++)
    {
        CGPoint point = pointsArray[i];
        greatestXValue = MAX(greatestXValue, point.x);
        greatestYValue = MAX(greatestYValue, point.y);
        smallestXValue = MIN(smallestXValue, point.x);
        smallestYValue = MIN(smallestYValue, point.y);
    }

    CGRect rect;
    rect.origin = CGPointMake(smallestXValue, smallestYValue);
    rect.size.width = greatestXValue - smallestXValue;
    rect.size.height = greatestYValue - smallestYValue;

    return rect;
}

Can be used like this

CGPoint poinstArray[] = {topLeft, bottomRight};
CGRect smallestRect = CGRectSmallestWithCGPoints(poinstArray, 2);

Upvotes: 5

jscs
jscs

Reputation: 64022

Hopefully you're only talking about this one shape, always oriented this way, otherwise this becomes a tricky computational geometry problem (something like the largest enclosed rectangle in a concave polygon).

Given your list of points, the following should work:

  1. a. Find the point with the largest y value.
    b. Find the other point with an equally large y value.
    c. Compare the x values of these two and determine which is leftmost.

  2. Find the minimum y value of all the points.

  3. Create two new points, each with an x value equal to one of the points you found in step 1, and with the y value found in step 2.

  4. The two points from step 1 are your top left and right points, and the two created in step 3 are the bottom left and right. You can now construct the final rectangle.

Upvotes: 1

Manlio
Manlio

Reputation: 10864

If I did not misunderstand the question, your aim is to find the blue points:
enter image description here

If I'm correct, then it's enough for you to store two points (say topL and topR) and a value (say bottom).

enter image description here

Iteratively:

  • check if the current point has y < topL.y and eventually update topL and topR.
    • If instead y == topL.y check if current x is less than topL.x. If yes update topL
    • otherwise check if current x>topR.x; if yes update topR.
  • check if current y>bottom. If yes update bottom.

Note that when I say "update topL" I mean both x and y.

At the end you can get your bottom-left and bottom-right points using x coordinate of topL and topR and setting y coordinate to bottom.

Upvotes: 2

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