A recent comment on one of the Java2D support lists indicated that
developers wishing to rotate a transform based on a point in space
or a vector need to use the atan2() method to turn that vector into
an angle measurement only to have the rotation methods on AffineTransform
use sin() and cos() to turn that angle back into components of a vector.

This is a lot of calculations to massage the vector/point data into
a form usable to adjust the transformation matrix when a simple
vector normalization would suffice. In other words cos(atan2(y,x))
and sin(atan2(y,x)) are simply the X and Y components of a normalized
vector pointing at (x,y).

To simplify this process and avoid the math rounding errors that the
customer was encountering from the trigonometric functions, we should
offer the following new methods on AffineTransform:

AffineTransform.rotate(double vecX, double vecY);
AffineTransform.rotate(double vecX, double vecY,
                       double centerX, double centerY);
AffineTransform.setToRotation(<similar argument lists>);
AffineTransform.getRotateInstance(<similar argument lists>);

The first instance is equivalent to rotate(Math.atan2(y, x)) and the
second is equivalent to rotate(Math.atan2(vecY, vecX), centerX, centerY);

Additionally, for the very common cases of quadrant rotation, dealing with trigonometric functions is very imprecise and unnecessary as the operations are very simple and fast to implement. For these cases, we should also add quadrant rotation methods:

AffineTransform.quadrantrotate(int numquadrants);
AffineTransform.quadrantrotate(int numquadrants,
                               double centerX, double centerY);
AffineTransform.setToQuadrantRotation(<similar argument lists>);
AffineTransform.getQuadrantRotateInstance(<similar argument lists>);
###@###.### 10/12/04 23:51 GMT