Draw lines between points(multiple)

Question

with the help i am able to draw circle with the coordinated using:

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 5.0);
    CGContextSetStrokeColorWithColor(context,[UIColor grayColor].CGColor);
    /**** Get values from reponse and fill it in this array.   ******/
    NSArray *objectCoords = [NSArray arrayWithObjects: @"{{20,80},{5,5}}", @"{{120,60},{5,5}}", @"{{60,84},{5,5}}", @"{{80,88},{5,5}}", @"{{100,93},{5,5}}", @"{{20,20},{5,5}}", @"{{160,70},{5,5}}", @"{{128,68},{5,5}}", @"{{90,60},{5,5}}", @"{{110,80},{5,5}}", nil];
    for (NSString* objectCoord in objectCoords) {
        CGRect coord = CGRectFromString(objectCoord);
        // Draw using your coord
        CGContextAddEllipseInRect(context, coord);
    }

Now what i am trying to achieve is draw lines between the points(circle),as shown in the attached image.I know we can draw a line between 2 points, but here in this case, the lines needs to be drawn between one to multiple point/circle .Please suggest me to achieve this result. expected output

Rob · Accepted Answer

You can just draw multiple lines. First, come up with a model to represent between which points you want to draw lines. For example, you could have an array of lines, where each line is defined, itself, as an array with the indices of two points, the starting point and the ending point.

For example, if you want to draw lines from point 1 to 3, 4, and 5, and from point 3 to 4 and 5, and between 4 and 5, you could do something like:

CGContextSetLineWidth(context, 1.0);

NSArray *lines = @[@[@(1), @(3)],
                   @[@(1), @(4)],
                   @[@(1), @(5)],
                   @[@(3), @(4)],
                   @[@(3), @(5)],
                   @[@(4), @(5)]];

for (NSArray *points in lines) {
    NSInteger startIndex = [points[0] integerValue];
    NSInteger endIndex   = [points[1] integerValue];

    CGRect startRect = CGRectFromString(objectCoords[startIndex]);
    CGRect endRect   = CGRectFromString(objectCoords[endIndex]);

    CGContextMoveToPoint(context, CGRectGetMidX(startRect), CGRectGetMidY(startRect));
    CGContextAddLineToPoint(context, CGRectGetMidX(endRect), CGRectGetMidY(endRect));
}

CGContextDrawPath(context, kCGPathStroke);

There are tons of different ways of doing it, but just come up with some model that represents where you want to draw the lines, and then iterate through that model to draw all of the individual lines.

If you wanted to have every point draw lines to the three closest points (which is not what your picture does, but it's what you asked for in a subsequent comment), you can:

build array of indices, indices in your objectCoords array; and
now iterate through each point in objectCoords:
- build new array of indices, sortedIndices, sorted by the distance that the point represented by that index is from the current object in objectCoords; and
- draw the three closest lines.

Thus:

// build array of indices (0, 1, 2, ...)

NSMutableArray *indices = [NSMutableArray array];
[objectCoords enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    [indices addObject:@(idx)];
}];

// now go through all of the points in objectCoords

[objectCoords enumerateObjectsUsingBlock:^(NSString *obj, NSUInteger idx, BOOL *stop) {

    // build new array of indices sorted by distance from the current point

    NSArray *sortedIndices = [indices sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        CGFloat distance1 = [self distanceFromPointAtIndex:idx
                                            toPointAtIndex:[obj1 integerValue]
                                         usingObjectCoords:objectCoords];

        CGFloat distance2 = [self distanceFromPointAtIndex:idx
                                            toPointAtIndex:[obj2 integerValue]
                                         usingObjectCoords:objectCoords];

        if (distance1 < distance2)
            return NSOrderedAscending;
        else if (distance1 > distance2)
            return NSOrderedDescending;
        return NSOrderedSame;
    }];

    // now draw lines to the three closest indices
    // (skipping 0, because that's probably the current point)

    for (NSInteger i = 1; i < 4 && i < [sortedIndices count]; i++) {

        NSInteger index = [sortedIndices[i] integerValue];

        CGRect startRect = CGRectFromString(objectCoords[idx]);
        CGRect endRect   = CGRectFromString(objectCoords[index]);

        CGContextMoveToPoint(context,    CGRectGetMidX(startRect), CGRectGetMidY(startRect));
        CGContextAddLineToPoint(context, CGRectGetMidX(endRect),   CGRectGetMidY(endRect));
    }
}];

CGContextSetLineWidth(context, 1);
CGContextDrawPath(context, kCGPathStroke);

And this uses the following method to calculate the distance between two points:

- (CGFloat)distanceFromPointAtIndex:(NSInteger)index1 toPointAtIndex:(NSInteger)index2 usingObjectCoords:(NSArray *)objectCoords
{
    CGRect rect1 = CGRectFromString(objectCoords[index1]);
    CGRect rect2 = CGRectFromString(objectCoords[index2]);

    return hypotf(CGRectGetMidX(rect1) - CGRectGetMidX(rect2), CGRectGetMidY(rect1) - CGRectGetMidY(rect2));
}

Using the objectCoords in your original example, that yields:

points with lines b/w three closest for each

Draw lines between points(multiple)

Answers (2)

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