findPointOnTangentOnCircleWithCenter

gistfile1.m

+(double)distanceBetweenPoint:(CGPoint)pointA andAnotherPoint:(CGPoint)pointB
{
    return sqrt((pointA.x - pointB.x)*(pointA.x - pointB.x) + (pointA.y - pointB.y)*(pointA.y - pointB.y));
}

+(NSArray *)findPointOnTangentOnCircleWithCenter:(CGPoint)center Radius:(double)radius pointOnTangent:(CGPoint)point
{
    double dx = center.x - point.x;
    double dy = center.y - point.y;
    double distance = [EXMathBrain distanceBetweenPoint:center andAnotherPoint:point];
    double alfa = atan2(dy, dx);
    double beta = asin(radius/distance);
    double segmentLen = sqrt(distance*distance - radius*radius);
    
    NSMutableArray *results = [NSMutableArray arrayWithCapacity:2];
    
    dx = cos(alfa+beta)*segmentLen;
    dy = sin(alfa+beta)*segmentLen;
    [results addObject:[NSValue valueWithCGPoint:CGPointMake(point.x+dx, point.y+dy)]];
    
    dx = cos(alfa-beta)*segmentLen;
    dy = sin(alfa-beta)*segmentLen;
    [results addObject:[NSValue valueWithCGPoint:CGPointMake(point.x+dx, point.y+dy)]];
    
    return results;
}