diva.canvas
Class TransformContext

java.lang.Object
  diva.canvas.TransformContext

public class TransformContext
extends java.lang.Object

A transform context defines a transformed coordinate system. Each transform context is associated with a component in the display tree. This class provides the support for most of the transform-related operations on the display tree.

Version:

$Id: TransformContext.java 38798 2005-07-08 20:00:01Z cxh $

Author:

John Reekie

Accepted Rating:

Yellow

Field Summary

private boolean	_cacheValid A flag saying whether the cached data is valid.
private CanvasComponent	_component The component associated with this context
private java.awt.geom.AffineTransform	_graphicsTransform The temporary graphics context transform
private java.awt.geom.AffineTransform	_inverseTransform The transform from the parent context to this context
private java.awt.geom.AffineTransform	_screenTransform The cached local-to-screen coordinate transform
private java.awt.geom.AffineTransform	_transform The main transform, which is from this context to the parent context
private int	_version The version number

Constructor Summary

TransformContext(CanvasComponent component)
Create a transform context associated with the given display component.

Method Summary

void	checkCacheValid(TransformContext ancestor) Check transform cache validity.
void	concatenate(java.awt.geom.AffineTransform at) Concatenate this transform context with the given transform.
CanvasComponent	getComponent() Get the component that this context is associated with.
java.awt.geom.AffineTransform	getInverseTransform() Get the transform from parent coordinates into local coordinates.
TransformContext	getParent() Get the parent transform context of this one, or null if this context is at the root of the transform tree.
java.awt.geom.AffineTransform	getScreenTransform() Get the transform from local coordinates into screen coordinates.
java.awt.geom.AffineTransform	getTransform() Get the transform of this context.
java.awt.geom.AffineTransform	getTransform(TransformContext context) Get the transform of this context, relative to the given context.
int	getVersion() Get the version number of the transform context.
void	invalidateCache() Notify that cached data based on the transform is now invalid.
boolean	isCacheValid() Test if the cache is valid.
void	pop(java.awt.Graphics2D g) Pop this transform off the graphics stack.
void	preConcatenate(java.awt.geom.AffineTransform at) Pre-concatenate this transform context with the given transform.
void	push(java.awt.Graphics2D g) Push this transform onto the graphics stack.
void	setTransform(java.awt.geom.AffineTransform at) Set the transform that maps local coordinates into the parent's coordinates.
void	translate(double x, double y) Translate this context the given distance.
private void	validateCache() Recompute the cached transforms.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_cacheValid

private boolean _cacheValid

A flag saying whether the cached data is valid.

_version

private int _version

The version number

_component

private CanvasComponent _component

The component associated with this context

_graphicsTransform

private java.awt.geom.AffineTransform _graphicsTransform

The temporary graphics context transform

_transform

private java.awt.geom.AffineTransform _transform

The main transform, which is from this context to the parent context

_inverseTransform

private java.awt.geom.AffineTransform _inverseTransform

The transform from the parent context to this context

_screenTransform

private java.awt.geom.AffineTransform _screenTransform

The cached local-to-screen coordinate transform

Constructor Detail

TransformContext

public TransformContext(CanvasComponent component)

Create a transform context associated with the given display component.

Method Detail

checkCacheValid

public void checkCacheValid(TransformContext ancestor)

Check transform cache validity. The argument is an ancestor context of this context. If the ancestor is not valid, then all of the contexts from this one up to the ancestor are marked invalid.

concatenate

public void concatenate(java.awt.geom.AffineTransform at)

Concatenate this transform context with the given transform.

getComponent

public CanvasComponent getComponent()

Get the component that this context is associated with. The component is set in the constructor and cannot be changed.

getInverseTransform

public java.awt.geom.AffineTransform getInverseTransform()

Get the transform from parent coordinates into local coordinates.

getParent

public TransformContext getParent()

Get the parent transform context of this one, or null if this context is at the root of the transform tree.

getScreenTransform

public java.awt.geom.AffineTransform getScreenTransform()

Get the transform from local coordinates into screen coordinates.

getTransform

public java.awt.geom.AffineTransform getTransform()

Get the transform of this context. This is the transform from this context into the parent's context.

getTransform

public java.awt.geom.AffineTransform getTransform(TransformContext context)

Get the transform of this context, relative to the given context. This is the transform from this context into the given context, which must enclose this one.

getVersion

public int getVersion()

Get the version number of the transform context. The version number is incremented whenever the transform changes, so can be used by client components to figure out when to update cached data based upon the transform.

invalidateCache

public void invalidateCache()

Notify that cached data based on the transform is now invalid. Increment the version number so that clients can use it to tell if they need to update data based on the transform.

isCacheValid

public boolean isCacheValid()

Test if the cache is valid.

push

public void push(java.awt.Graphics2D g)

Push this transform onto the graphics stack.

pop

public void pop(java.awt.Graphics2D g)

Pop this transform off the graphics stack.

preConcatenate

public void preConcatenate(java.awt.geom.AffineTransform at)

Pre-concatenate this transform context with the given transform.

setTransform

public void setTransform(java.awt.geom.AffineTransform at)

Set the transform that maps local coordinates into the parent's coordinates. If there is no parent, the "parent" is taken to be the screen. An exception will be thrown if the transform is null. This method invalidates any cached transforms. Note that the transform may be remembered by this context, so the caller must make sure that it will not be subsequently modified.

translate

public void translate(double x,
                      double y)

Translate this context the given distance.

validateCache

private void validateCache()

Recompute the cached transforms.