Question

My code:

CGFloat scaleFactor = newSize.width / oldSize.width;
CGFloat newCenterX = center_.x * scaleFactor;
CGFloat newCenterY = center_.y * scaleFactor;

CGPoint newCenter = CGPointMake(newCenterX, newCenterY);
//newCenter.x = newCenterX;
//newCenter.y = newCenterY;

CGFloat newRaduis = raduis_ * scaleFactor;
newCenter.y += newSize.height - ceilf(scaleFactor) * oldSize.height;
NSLog(@"Convertion from %@ to %@", NSStringFromCGSize(oldSize), NSStringFromCGSize(newSize));
NSLog(@"old center = %@, old radius = %f", NSStringFromCGPoint(center_), raduis_);
NSLog(@"new center = %@, new radius = %f", NSStringFromCGPoint(newCenter), newRaduis);
NSLog(@"new center x = %f, new center y = %f", newCenterX, newCenterY);

And output:

2012-09-14 14:18:35.027 TestApp[425:4b93] Convertion from {1080, 1920} to {320, 415}
2012-09-14 14:18:35.031 TestApp[425:4b93] old center = {246, 822}, old radius = 20.000000
2012-09-14 14:18:35.033 TestApp[425:4b93] new center = {73, -1261}, new radius = 5.925926
2012-09-14 14:18:35.035 TestApp[425:4b93] new center x = 73, new center y = 244

In output – new center = {73, -1261}, new radius = 5.925926. Why center y value is negative? What I do wrong?

Thanks in advance for help

Answer 1

The error is because of your line

newCenter.y += newSize.height - ceilf(scaleFactor) * oldSize.height;

• scaleFactor is about 0.2962 so ceilf(scaleFactor) is equal to 1.
• newSize.height is 415, oldSize.height is 1920, so 415 - 1*1920 is -1505, and newCenter.y += -1505 makes newCenter.y change from 243.556 to 243.556 + (-1505) = 1261.444.

So this seems legit that newCenter.y is -1261 after this line.