The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
You can modify the transform attribute in the Graphics2D
context to move, rotate, scale, and shear graphics primitives when they are rendered. The transform attribute is defined by an instance of the
AffineTransform
class. An affine transform is a transformation such as translate, rotate, scale, or shear in which parallel lines remain parallel even after being transformed.
The
Graphics2D
class provides several methods for changing the transform attribute. You can construct a new AffineTransform
and change the Graphics2D
transform attribute by calling transform
.
AffineTransform
defines the following factory methods to make it easier to construct new transforms:
getRotateInstance
getScaleInstance
getShearInstance
getTranslateInstance
Alternatively you can use one of the Graphics2D
transformation methods to modify the current transform. When you call one of these convenience methods, the resulting transform is concatenated with the current transform and is applied during rendering:
rotate
to specify an angle of rotation in radiansscale
to specify a scaling factor in the x and y directionsshear
to specify a shearing factor in the x and y directionstranslate
to specify a translation offset in the x and y directionsYou can also construct an AffineTransform
object directly and concatenate it with the current transform by calling the transform
method.
The drawImage
method is also overloaded to allow you to specify an AffineTransform
that is applied to the image as it is rendered. Specifying a transform when you call drawImage
does not affect the Graphics2D
transform attribute.
The following program is the same as StrokeandFill
, but also allows the user to choose a transformation to apply to the selected object when it is rendered.
contains the complete code for this applet.Transform.java
When a transform is chosen from the Transform menu, the transform is concatenated onto the AffineTransform
at
:
public void setTrans(int transIndex) { // Sets the AffineTransform. switch ( transIndex ) { case 0 : at.setToIdentity(); at.translate(w/2, h/2); break; case 1 : at.rotate(Math.toRadians(45)); break; case 2 : at.scale(0.5, 0.5); break; case 3 : at.shear(0.5, 0.0); break; } }
Before displaying the shape corresponding to the menu choices, the application first retrieves the current transform from the Graphics2D
object:
AffineTransform saveXform = g2.getTransform();
This transform will be restored to the Graphics2D
after rendering.
After retrieving the current transform, another AffineTransform
, toCenterAt
, is created that causes shapes to be rendered in the center of the panel. The at
AffineTransform
is concatenated onto toCenterAt
:
AffineTransform toCenterAt = new AffineTransform(); toCenterAt.concatenate(at); toCenterAt.translate(-(r.width/2), -(r.height/2));
The toCenterAt
transform is concatenated onto the Graphics2D
transform with the transform
method:
g2.transform(toCenterAt);
After rendering is completed, the original transform is restored using the setTransform
method:
g2.setTransform(saveXform);
setTransform
method to concatenate a coordinate transform onto an existing transform. The setTransform
method overwrites the Graphics2D
object's current transform, which might be needed for other reasons, such as positioning Swing and lightweight components in a window. Use these steps to perform transformations:
getTransform
method to get the current transform.transform
, translate
, scale
, shear
, or rotate
to concatenate a transform.setTransform
method.