Transform from quadrilateral to quadrilateral with AffineTransform?

Question

Is Java's AffineTransform insufficient to hold transformation from one convex quadrilateral to another?

Is this true, that transformation between convex quadrilaterals is fully covered by perspective transform?

Perspective matrix has 8 elements, while Java's has 6. Does this mean that here are insufficient coefficients?

This means that I can't code GUI where user would drag quadrilateral corners and get quadrilateral content transformed correspondently?

How can this be?

Answer 1

An affine transformation maintains parallel lines as parallel. A perspective transform is by definition does not, and therefore is not affine.

A perspective transfrom is included with the JAI ("Java Advanced Imaging") API but I'm not sure what's the official source for it after Oracle bought Sun.