//Mouse drag, calculate rotation
public void drag(Point NewPt, Quat4f NewRot)
{
//Map the point to the sphere
this.mapToSphere(NewPt, EnVec);
//Return the quaternion equivalent to the rotation
if (NewRot != null)
{
Vector3f Perp = new Vector3f();
//Compute the vector perpendicular to the begin and end vectors
Vector3f.cross(Perp, StVec, EnVec);
//Compute the length of the perpendicular vector
if (Perp.length() > Epsilon)
//if its non-zero
{
//We're ok, so return the perpendicular vector as the transform after all
NewRot.x = Perp.x;
NewRot.y = Perp.y;
NewRot.z = Perp.z;
//In the quaternion values, w is cosine (theta / 2), where theta is the rotation angle
NewRot.w = Vector3f.dot(StVec, EnVec);
}
//if it is zero
else
{
//The begin and end vectors coincide, so return an identity transform
NewRot.x = NewRot.y = NewRot.z = NewRot.w = 0.0f;
}
}
}
private void drag(Point MousePt)
{
Quat4f ThisQuat = new Quat4f();
arcBall.drag(MousePt, ThisQuat); // Update End Vector And Get Rotation As Quaternion
lock (matrixLock)
{
ThisRot.Rotation = ThisQuat; // Convert Quaternion Into Matrix3fT
ThisRot.mul(ThisRot, LastRot); // Accumulate Last Rotation Into This One
}
}
private void drag_Transfer(Point MousePt)
{
Quat4f ThisQuat = new Quat4f();
arcBall.drag(MousePt, ThisQuat); // Update End Vector And Get Rotation As Quaternion
lock (matrixLock)
{
//lock 的目的很明确：就是不想让别人使用这段代码，
//体现在多线程情况下，只允许当前线程执行该代码区域，
//其他线程等待直到该线程执行结束；这样可以多线程避免同时使用某一方法造成数据混乱。
ThisRot.Transfer = ThisQuat; // Convert Quaternion Into Matrix3fT
ThisRot.mul(ThisRot, LastRot); // Accumulate Last Rotation Into This One
}
}