Java Reference
In-Depth Information
The AffineTransform Class
In Java, the
AffineTransform
class in the
java.awt.geom
package represents an affine
transformation. Every
Graphics2D
graphics context has one. The default
AffineTransform
object
in a graphics context is the
identity transform
, which leaves user coordinates unchanged. It is applied to
the user coordinate system anyway for everything you draw, but all the coordinates are unaltered by
default. You can retrieve a copy of the current transform for a graphics context object by calling its
getTransform()
method. For example:
AffineTransform at = g2D.getTransform(); // Get current transform
While this retrieves a copy of the current transform for a graphics context, you can also set it with
another transform object:
g2D.setTransform(at);
You can retrieve the transform currently in effect with
getTransform()
, set it to some other
operation before you draw some shapes, and then restore the original transform later with
setTransform()
when you're finished. The fact that
getTransform()
returns a reference to a copy
rather than a reference to the original transform object is important. It means you can alter the existing
transform and then restore the copy later.
Although the default transform object for a graphics context leaves everything unchanged, you could set
it to do something by calling one of its member functions. All of these have a return type of
void
so
none of them return anything:
Transform Default
Description
setToTranslation
(double deltaX,
double deltaY)
This method makes the transform a translation of
deltaX
in
x
and
deltaY
in
y
. This replaces whatever the previous transform was for
the graphics context. You could apply this to the transform for a
graphics context with the statements:
// Save current transform and set a new one
AffineTransform at = g2D.getTransform();
at.setToTranslation(5.0, 10.0);
The effect of the new transform will be to shift everything that is
drawn in the graphics context,
g2D
, 5.0 to the right, and down by
10.0. This will apply to everything that is drawn in
g2D
subsequent
to the statement that sets the new transform.
