CODEWITHSUNDEEP
iosobjective-ccocoa-touchuiviewdrawrect
Josue Espinosa
Josue Espinosa

Reputation: 5089

Center moving drawRect?

In my app, a circle is drawn based on a users drag. e.g. a user taps, that is the center of a circle that will be drawn, and as they drag their finger, the circle will grow to that point. This works, except for some reason the center moves down and to the right as the radius of the circle grows. Why is this happening? Here is what I am trying:

@implementation CircleView{
    CGPoint center;
    CGPoint endPoint;
    CGFloat distance;
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    center = [touch locationInView:self];
    [self setNeedsDisplay];
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [touches anyObject];
    endPoint = [touch locationInView:self];
    CGFloat xDist = (endPoint.x - center.x);
    CGFloat yDist = (endPoint.y - center.y);
    distance = sqrt((xDist * xDist) + (yDist * yDist));
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect{
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 2.0);
    CGContextSetStrokeColorWithColor(context, [UIColor blueColor].CGColor);
    CGRect rectangle = CGRectMake(center.x,center.y,distance, distance);
    CGContextAddEllipseInRect(context, rectangle);
    CGContextStrokePath(context);
}

What should be happening is that center point never ever moves, and the circle should just grow. Any ideas?

Upvotes: 0

Views: 553

Answers (3)

Josue Espinosa
Josue Espinosa

Reputation: 5089

CGRect rectangle = CGRectMake(center.x - distance, center.y - distance, distance * 2, distance * 2);

Upvotes: 0

rmaddy
rmaddy

Reputation: 318864

CGRect rectangle = CGRectMake(center.x,center.y,distance, distance);

should be:

CGRect rectangle = CGRectMake(center.x - distance, center.y - distance, distance * 2, distance * 2);

Upvotes: 1

DrummerB
DrummerB

Reputation: 40211

Because in CGRectMake you have to specify the origin (and the size) of the rectangle, not the center.

Upvotes: 1

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