Vector Algebra

static inline CGVector TCVectorMultiply(CGVector vector, CGFloat m);

static inline CGVector TCVectorMinus(CGPoint p1, CGPoint p2)
{
    return CGVectorMake(
        p1.x - p2.x,
        p1.y - p2.y
    );
}

static inline CGFloat TCVectorLength(CGVector vector)
{
    return sqrtf(vector.dx * vector.dx + vector.dy * vector.dy);
}

static inline CGVector TCVectorUnit(CGVector vector)
{
    CGFloat invLen = 1.0 / TCVectorLength(vector);
    return TCVectorMultiply(vector, invLen);
}

static inline CGVector TCVectorMultiply(CGVector vector, CGFloat m)
{
    return CGVectorMake(
        vector.dx * m,
        vector.dy * m
    );
}

----------------------------------------------------------------


static inline CGPoint CGPointMultiplyScalar( const CGPoint a, const CGFloat b )
{
  return CGPointMake(a.x * b, a.y * b);
}


static inline CGPoint CGPointAdd( const CGPoint a, const CGPoint b)
{
  return CGPointMake(a.x + b.x , a.y + b.y);
}