acm.graphics
Class GCanvas

java.lang.Object
  java.awt.Component
      java.awt.Container
          acm.graphics.GCanvas

public class GCanvas
extends Container
implements GContainer

The GCanvas class is a lightweight component that also serves as a container for graphical objects. As such, this class provides the link between graphical objects and the window system. Conceptually, the GCanvas provides a background canvas to which other graphical objects can be added.

Field Summary

Constructor Summary

GCanvas()

Method Summary

Component	add(Component comp) Adds the component to this canvas without changing its location.
void	add(Component comp, double x, double y) Adds the component to this canvas and sets its location to the point (x, y).
void	add(Component comp, GPoint pt) Adds the component to this canvas and sets its location to the specified point.
void	add(GObject gobj) Adds the graphical object to this canvas.
void	add(GObject gobj, double x, double y) Adds the graphical object to this canvas and sets its location to the point (x, y).
void	add(GObject gobj, GPoint pt) Adds the graphical object to this canvas and sets its location to the specified point.
boolean	getAutoRepaintFlag() Returns the current setting of the auto-repaint flag as described in setAutoRepaintFlag.
GObject	getElement(int index) Returns the graphical object at the specified index, numbering from back to front in the the z dimension.
GObject	getElementAt(double x, double y) Returns the topmost graphical object that contains the point (x, y), or null if no such object exists.
GObject	getElementAt(GPoint pt) Returns the topmost graphical object that contains the specified point, or null if no such object exists.
int	getElementCount() Returns the number of graphical objects stored in this GCanvas.
int	getHeight() Returns the height of this canvas in pixels.
boolean	getNativeArcFlag() Returns the current setting of the native-arc flag as described in setNativeArcFlag.
int	getWidth() Returns the width of this canvas in pixels.
Iterator<GObject>	iterator() Returns an Iterator that cycles through the elements within this container in the default direction, which is from back to front.
Iterator<GObject>	iterator(int direction) Returns an Iterator that cycles through the elements within this container in the specified direction, which must be one of the constants GContainer.FRONT_TO_BACK or GContainer.BACK_TO_FRONT.
void	remove(Component comp) Removes the component from the canvas.
void	remove(GObject gobj) Removes a graphical object from this GCanvas.
void	removeAll() Removes all graphical objects from this GCanvas.
void	setAutoRepaintFlag(boolean state) Changes the setting of the auto-repaint flag.
void	setNativeArcFlag(boolean state) Sets whether the redering code for GArc and GOval should use Java arcs.

Constructor Detail

public GCanvas()

Creates a new GCanvas that contains no objects.

Usage:

GCanvas gc = new GCanvas();

Method Detail

public Component add(Component comp)

Adds the component to this canvas without changing its location. If the component has no size, its size is set to its preferred size. The return type is Component to match the method in the Container class, but the result is typically ignored.

Usage:

gc.add(comp);

Parameter:

comp	The component to add

public final void add(Component comp, double x, double y)

Adds the component to this canvas and sets its location to the point (x, y).

Usage:

gc.add(comp, x, y);

Parameters:

comp	The component to add
x	The new x-coordinate for the object
y	The new y-coordinate for the object

public final void add(Component comp, GPoint pt)

Adds the component to this canvas and sets its location to the specified point.

Usage:

gc.add(comp, pt);

Parameters:

comp	The component to add
pt	A GPoint object giving the coordinates of the point

public void add(GObject gobj)

Adds the graphical object to this canvas.

Usage:

gc.add(gobj);

Parameter:

gobj	The graphical object to add

Specified by:

add in interface GContainer

public final void add(GObject gobj, double x, double y)

Adds the graphical object to this canvas and sets its location to the point (x, y).

Usage:

gc.add(gobj, x, y);

Parameters:

gobj	The graphical object to add
x	The new x-coordinate for the object
y	The new y-coordinate for the object

Specified by:

add in interface GContainer

public final void add(GObject gobj, GPoint pt)

Adds the graphical object to this canvas and sets its location to the specified point.

Usage:

gc.add(gobj, pt);

Parameters:

gobj	The graphical object to add
pt	A GPoint object giving the coordinates of the point

Specified by:

add in interface GContainer

public boolean getAutoRepaintFlag()

Returns the current setting of the auto-repaint flag as described in setAutoRepaintFlag.

Usage:	if (gc.getAutoRepaintFlag()) . . .
Returns:	true if auto-repaint mode is enabled, and false otherwise

public GObject getElement(int index)

Returns the graphical object at the specified index, numbering from back to front in the the z dimension.

Usage:

GObject gobj = gc.getElement(index);

Parameter:

index

The index of the component to return

Returns:

The graphical object at the specified index

Specified by:

getElement in interface GContainer

public GObject getElementAt(double x, double y)

Returns the topmost graphical object that contains the point (x, y), or null if no such object exists.

Usage:

GObject gobj = gc.getElementAt(x, y);

Parameters:

x	The x-coordinate of the point being tested
y	The y-coordinate of the point being tested

Returns:

The graphical object at the specified location, or null if no such object exists

Specified by:

getElementAt in interface GContainer

public final GObject getElementAt(GPoint pt)

Returns the topmost graphical object that contains the specified point, or null if no such object exists.

Usage:

GObject gobj = gc.getElementAt(pt);

Parameter:

pt	The coordinates being tested

Returns:

The graphical object at the specified location, or null if no such object exists

Specified by:

getElementAt in interface GContainer

public int getElementCount()

Returns the number of graphical objects stored in this GCanvas.

Usage:	int n = gc.getElementCount();
Returns:	The number of graphical objects in this GCanvas

Specified by:

getElementCount in interface GContainer

public int getHeight()

Returns the height of this canvas in pixels. This method is defined in JDK 1.2 components, but not in earlier ones. Defining this method here makes this entry available in all browsers.

Usage:	int height = gc.getHeight();
Returns:	The height of this canvas in pixels

public boolean getNativeArcFlag()

Returns the current setting of the native-arc flag as described in setNativeArcFlag.

Usage:	if (gc.getNativeArcFlag()) . . .
Returns:	true if native arcs are enabled, and false otherwise

public int getWidth()

Returns the width of this canvas in pixels. This method is defined in JDK 1.2 components, but not in earlier ones. Defining this method here makes this entry available in all browsers.

Usage:	int width = gc.getWidth();
Returns:	The width of this canvas

public Iterator<GObject> iterator()

Returns an Iterator that cycles through the elements within this container in the default direction, which is from back to front. You can also run the iterator in the opposite direction by using the iterator(direction) form of this method.

Usage:	Iterator i = gc.iterator();
Returns:	An Iterator ranging over the elements of the container from back to front

public Iterator<GObject> iterator(int direction)

Returns an Iterator that cycles through the elements within this container in the specified direction, which must be one of the constants GContainer.FRONT_TO_BACK or GContainer.BACK_TO_FRONT.

      for (Iterator<GObject> i = gc.iterator(direction); i.hasNext(); )
 

Usage:	Iterator i = gc.iterator(direction);
Returns:	An Iterator ranging over the elements of the container in the specified direction

public void remove(Component comp)

Removes the component from the canvas.

Usage:

gc.remove(comp);

Parameter:

comp	The component to remove

public void remove(GObject gobj)

Removes a graphical object from this GCanvas.

Usage:

gc.remove(gobj);

Parameter:

gobj	The graphical object to remove

Specified by:

remove in interface GContainer

public void removeAll()

Removes all graphical objects from this GCanvas.

Usage:

gc.removeAll();

Specified by:

removeAll in interface GContainer

public void setAutoRepaintFlag(boolean state)

Changes the setting of the auto-repaint flag. By default, any change to a graphical object contained in this canvas automatically triggers a repaint of the canvas as a whole. While this behavior makes it much easier to use the package, it has the disadvantage that repaint requests come much more frequently than necessary. You can disable this feature by calling setAutoRepaintFlag(false), but you must then make explicit calls to repaint() whenever you want to update the display. The advantage of this model is that you can then make many different changes and have them all appear at once with a single repaint call.

Usage:

gc.setAutoRepaintFlag(state);

Parameter:

state

true to enable auto-repaint mode, and false to disable it

public void setNativeArcFlag(boolean state)

Sets whether the redering code for GArc and GOval should use Java arcs. By default, arcs and ovals are rendered using polygons and polylines to ensure that the same set of pixels is covered by the fill and frame. If this value is set to true, the renderers will use the native arc code, which is more efficient but less accurate.

Usage:

gc.setNativeArcFlag(state);

Parameter:

state

true to enable native arcs, false to use polygons