How to drag a view, along the circumference of an oval? - iphone

Question

I have an Oval and a view on the circumference of the Oval. When you try to drag the view, the view should be moved only on the circumference of the Oval. How can I achieve this?
Any sample equation would be helpful. Thanks.

Answer 1

CGPoint ovalCenter;
CGSize ovalSize;
- (CGPoint)constrainPointToOval:(CGPoint)point
{
float angle = atan2(point.y - ovalCenter.y, point.x - ovalCenter.x);
return CGPointMake(ovalSize.width * cosf(angle), ovalSize.height * sinf(angle));
}
You'll need to set ovalCenter and ovalSize elsewhere. Then run the touch position through this before setting the location of the view.

Answer 2

I have figured out a solution for getting a constrained drag along the sides of a square.
If anyone can improve the code, or have a better solution, you most welcome.
- (CGPoint) constrainPointToSquare:(CGPoint) point
{
float pi = 3.14159265;
float s1,s2;
CGPoint squareDragPoint;
float squareSize = 200.0;
float angle;
angle = atan2 (point.y - mCenter.y, point.x - mCenter.x);
float x1 = point.x;
float x2 = mCenter.x;
float y1 = point.y;
float y2 = mCenter.y;
if (((3*(pi/4) <= angle && pi >= angle) || (-pi <= angle && -3*(pi/4) >= angle)))//left
{
s1 = y2 - squareSize;
s2 = x2 - squareSize * ((y1-y2)/(x1-x2));
squareDragPoint = CGPointMake(s1, s2);
}
else if (((-(pi/4) <= angle && 0.0 >= angle) || (0.0 <= angle && (pi/4) >= angle))) //right
{
s1 = y2 + squareSize;
s2 = x2 + squareSize * ((y1-y2)/(x1-x2));
squareDragPoint = CGPointMake(s1, s2);
}
else if (((-3*(pi/4) <= angle && -(pi/2) >= angle) || (-(pi/4) >= angle && -(pi/2) <= angle))) //top
{
s1 = x2 - squareSize;
s2 = y2 - squareSize * ((x1-x2)/(y1-y2));
squareDragPoint = CGPointMake(s2, s1);
}
else if (((3*(pi/4) >= angle && (pi/2) <= angle) || (pi/4 <= angle && (pi/2) >= angle))) //bottom
{
s1 = x2 + squareSize;
s2 = y2 + squareSize * ((x1-x2)/(y1-y2));
squareDragPoint = CGPointMake (s2, s1);
}
return squareDragPoint;
}