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Copyright © 2006 Sun Microsystems, Inc. All rights reserved.

java.awt
Class Graphics2D

java.lang.Object
  java.awt.Graphics
      java.awt.Graphics2D

public abstract class Graphics2D

extends Graphics

This Graphics2D class extends the Graphics class to provide more sophisticated control over graphics operations.

Coordinate Spaces

All coordinates passed to a Graphics2D object are specified in a device-independent coordinate system called User Space, which is used by applications. The Graphics2D object behaves as if it contains a transform object as part of its internal rendering state that defines how to convert coordinates from user space to device-dependent coordinates in Device Space.

Some of the operations performed by the rendering attribute objects occur in the device space, but all Graphics2D methods take user space coordinates.

Every Graphics2D object is associated with a target that defines where rendering takes place. A GraphicsConfiguration object defines the characteristics of the rendering target, such as pixel format and resolution. The same rendering target is used throughout the life of a Graphics2D object.

When creating a Graphics2D object, the GraphicsConfiguration specifies the transform for the target of the Graphics2D (a Component or Image). This transform maps the user space coordinate system to screen and printer device coordinates such that the origin maps to the upper left hand corner of the target region of the device with increasing X coordinates extending to the right and increasing Y coordinates extending downward. The scaling of the transform is set to identity for those devices that are close to 72 dpi, such as screen devices. The scaling of the transform is set to approximately 72 user space coordinates per square inch for high resolution devices, such as printers. For image buffers, the transform is the identity transform.

Rendering Process

The Rendering Process can be broken down into four phases that are controlled by the Graphics2D rendering attributes. The renderer can optimize many of these steps, either by caching the results for future calls, by collapsing multiple virtual steps into a single operation, or by recognizing various attributes as common simple cases that can be eliminated by modifying other parts of the operation.

The steps in the rendering process are:

1. Determine what to render.
2. Constrain the rendering operation to the current Clip. The Clip is specified by a Shape in user space and is controlled by the program using the various clip manipulation methods of Graphics . This user clip is transformed into device space by the target transform and combined with the device clip, which is defined by the visibility of windows and device extents. The combination of the user clip and device clip defines the composite clip, which determines the final clipping region. The user clip is not modified by the rendering system to reflect the resulting composite clip.
3. Determine what colors to render.
4. Apply the colors to the destination drawing surface using the current Composite attribute in the Graphics2D context.

The three types of rendering operations, along with details of each of their particular rendering processes are:

1. Shape operations
   1. If the operation is a draw operation, then the current Stroke attribute in the Graphics2D context is used to construct a new Shape object that contains the outline of the specified Shape.
   2. The Shape is transformed from user space to device space using the target transform in the Graphics2D context.
   3. The current Color in the Graphics2D context is used to determine the colors to render in device space.
2. Text operations
   1. The following steps are used to determine the set of glyphs required to render the indicated String:
      1. If the argument is a String, then the current Font in the Graphics2D context is asked to convert the Unicode characters in the String into a set of glyphs for presentation with whatever basic layout and shaping algorithms the font implements.
      2. If the argument is an AttributedCharacterIterator, its embedded font attributes are used to implement more sophisticated glyph layout algorithms .
   2. The current Font is queried to obtain outlines for the indicated glyphs. These outlines are treated as shapes in user space relative to the position of each glyph that was determined in step 1.
   3. The character outlines are filled as indicated above under Shape operations.
   4. The current Color is used to determine the colors to render in device space.
3. Image Operations
   1. The region of interest is defined by the bounding box of the source Image. This bounding box is specified in Image Space, which is the Image object's local coordinate system.
   2. In this Profile, the bounding box is always treated as if it is already in user space.
   3. The bounding box of the source Image is transformed from user space into device space using the target transform . Note that the result of transforming the bounding box does not necessarily result in a rectangular region in device space.
   4. The Image object determines what colors to render, sampled according to the source to destination coordinate mapping specified by the target transform .

Default Rendering Attributes

The default values for the Graphics2D rendering attributes are:

Color

The color of the Component.

Font

The Font of the Component.

Stroke

A square pen with a linewidth of 1, no dashing, miter segment joins and square end caps (unless restricted - see restrictions in BasicStroke) .

Composite

The AlphaComposite.SRC_OVER rule.

Clip

No rendering Clip, the output is clipped to the Component.

Restrictions

• Only instances of AlphaComposite are permitted when setting the Composite of the graphics context. See:
  • setComposite(java.awt.Composite)
• Only instances of BasicStroke are permitted when setting the Stroke of the graphics context. See:
  • setStroke(java.awt.Stroke)
  • BasicStroke
• A Graphics2D implementation may ignore the BasicStroke attributes end cap, line join, and miter limit. See:
  • setStroke(java.awt.Stroke)
  • BasicStroke
  • Profile-specific properties.

Constructor Summary

protected

Graphics2D() Constructs a new Graphics2D object.

Method Summary

abstract void	drawString(String str, int x, int y) Draws the text given by the specified string, using this graphics context's current font and color.
abstract Composite	getComposite() Returns the current Composite in the Graphics2D context.
abstract GraphicsConfiguration	getDeviceConfiguration() Returns the device configuration associated with this Graphics2D.
abstract Stroke	getStroke() Returns the current Stroke in the Graphics2D context.
abstract void	setComposite(Composite comp) Sets the Composite for the Graphics2D context.
abstract void	setStroke(Stroke s) Sets the Stroke for the Graphics2D context.

Methods inherited from class java.awt.Graphics

clearRect, clipRect, copyArea, create, create, dispose, draw3DRect, drawArc, drawBytes, drawChars, drawImage, drawImage, drawImage, drawImage, drawImage, drawImage, drawLine, drawOval, drawPolygon, drawPolygon, drawPolyline, drawRect, drawRoundRect, drawString, fill3DRect, fillArc, fillOval, fillPolygon, fillPolygon, fillRect, fillRoundRect, finalize, getClip, getClipBounds, getClipBounds, getClipRect, getColor, getFont, getFontMetrics, getFontMetrics, hitClip, setClip, setClip, setColor, setFont, setPaintMode, setXORMode, toString, translate

Methods inherited from class java.lang.Object

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

Constructor Detail

Graphics2D

protected Graphics2D()

Constructs a new Graphics2D object. Since Graphics2D is an abstract class, and since it must be customized by subclasses for different output devices, Graphics2D objects cannot be created directly. Instead, Graphics2D objects must be obtained from another Graphics2D object, created by a Component, or obtained from images such as BufferedImage objects.

See Also:

Component.getGraphics(), Graphics.create()

Method Detail

drawString

public abstract void drawString(String str,
                                int x,
                                int y)

Draws the text given by the specified string, using this graphics context's current font and color. The baseline of the leftmost character is at position (x, y) in this graphics context's coordinate system.

Specified by:

drawString in class Graphics

Parameters:

str - the string to be rendered

x - the x coordinate of the location where the String should be rendered

y - the y coordinate of the location where the String should be rendered

Throws:

NullPointerException - if str is null

Since:

JDK1.0

See Also:

Graphics.drawBytes(byte[], int, int, int, int), Graphics.drawChars(char[], int, int, int, int)

getDeviceConfiguration

public abstract GraphicsConfiguration getDeviceConfiguration()

Returns the device configuration associated with this Graphics2D.

Returns:

the device configuration of this Graphics2D.

setComposite

public abstract void setComposite(Composite comp)

Sets the Composite for the Graphics2D context. The Composite is used in all drawing methods such as drawImage, drawString, draw, and fill. It specifies how new pixels are to be combined with the existing pixels on the graphics device during the rendering process.

Note: This operation is subject to restriction in this Profile. If the Composite is a custom object rather than an instance of the AlphaComposite class then IllegalArgumentException is thrown.

Parameters:

comp - the Composite object to be used for rendering

Throws:

IllegalArgumentException - If comp is not an instance of AlphaComposite.

See Also:

getComposite(), AlphaComposite

setStroke

public abstract void setStroke(Stroke s)

Sets the Stroke for the Graphics2D context.

Parameters:

s - the Stroke object to be used to stroke a Shape during the rendering process

Note: This operation is subject to restriction in this Profile. If the Stroke is a custom object rather than an instance of the BasicStroke class then IllegalArgumentException is thrown.

See Also:

BasicStroke, getStroke()

getComposite

public abstract Composite getComposite()

Returns the current Composite in the Graphics2D context.

Returns:

the current Graphics2D Composite, which defines a compositing style.

See Also:

setComposite(java.awt.Composite)

getStroke

public abstract Stroke getStroke()

Returns the current Stroke in the Graphics2D context.

Returns:

the current Graphics2D Stroke, which defines the line style.

See Also:

setStroke(java.awt.Stroke)