shadingPattern matrix:

Matrix patternMatrix = shadingPattern.getMatrix();
AffineTransform transform = patternMatrix.createAffineTransform();

Point2D.Float p0 = new Point2D.Float(x0, y0);
Point2D.Float p1 = new Point2D.Float(x1, y1);
Point2D.Float deviceP0 = (Point2D.Float) transform.transform(p0, null);
Point2D.Float deviceP1 = (Point2D.Float) transform.transform(p1, null);