GCanvas (acm 2.1 API)

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

All Implemented Interfaces:

GContainer, java.awt.image.ImageObserver, java.awt.MenuContainer, java.io.Serializable
```
public class GCanvas
extends java.awt.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.

See Also:

Serialized Form

Nested Class Summary
- Nested classes/interfaces inherited from class java.awt.Container
  java.awt.Container.AccessibleAWTContainer
- Nested classes/interfaces inherited from class java.awt.Component
  java.awt.Component.AccessibleAWTComponent, java.awt.Component.BaselineResizeBehavior, java.awt.Component.BltBufferStrategy, java.awt.Component.FlipBufferStrategy

Field Summary
- Fields inherited from class java.awt.Component
  accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
- Fields inherited from interface acm.graphics.GContainer
  BACK_TO_FRONT, FRONT_TO_BACK
- Fields inherited from interface java.awt.image.ImageObserver
  ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

Constructors
Constructor and Description

GCanvas()
Creates a new GCanvas that contains no objects.

Constructors
Constructor and Description
`GCanvas()` Creates a new `GCanvas` that contains no objects.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`java.awt.Component`	`add(java.awt.Component comp)` Adds the component to this canvas without changing its location.
`void`	`add(java.awt.Component comp, double x, double y)` Adds the component to this canvas and sets its location to the point (`x`, `y`).
`void`	`add(java.awt.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.
`protected void`	`conditionalRepaint()` Repaints the canvas if auto-repaint is in effect.
`protected void`	`dispatchMouseEvent(java.awt.event.MouseEvent e)` Dispatches this mouse event to the uppermost graphical object for which the active point is within the object bounds.
`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.
`protected void`	`initOffscreenImage()` Initializes the offscreen memory image used for double buffering.
`boolean`	`isOpaque()` Returns a boolean value indicating whether this canvas is opaque.
`java.util.Iterator<GObject>`	`iterator()` Returns an `Iterator` that cycles through the elements within this container in the default direction, which is from back to front.
`java.util.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`	`paint(java.awt.Graphics g)` Paints the canvas.
`void`	`remove(java.awt.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`.
`protected void`	`sendBackward(GObject gobj)` Implements the `sendBackward` function from the `GContainer` interface.
`protected void`	`sendForward(GObject gobj)` Implements the `sendForward` function from the `GContainer` interface.
`protected void`	`sendToBack(GObject gobj)` Implements the `sendToBack` function from the `GContainer` interface.
`protected void`	`sendToFront(GObject gobj)` Implements the `sendToFront` function from the `GContainer` interface.
`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.
`void`	`setOpaque(boolean flag)` Sets a flag indicating whether this canvas is opaque, which means that it obscures anything behind it.
`void`	`update(java.awt.Graphics g)` Updates the canvas.
`protected void`	`updateEnabledList()` Reconstructs the enabledList list in the correct order.

Methods inherited from class java.awt.Container
add, add, add, add, addContainerListener, addImpl, addNotify, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, doLayout, findComponentAt, findComponentAt, getAlignmentX, getAlignmentY, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getInsets, getLayout, getListeners, getMaximumSize, getMinimumSize, getMousePosition, getPreferredSize, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, isValidateRoot, layout, list, list, locate, minimumSize, paintComponents, paramString, preferredSize, print, printComponents, processContainerEvent, processEvent, remove, removeContainerListener, removeNotify, setComponentZOrder, setFocusCycleRoot, setFocusTraversalKeys, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setFont, setLayout, transferFocusDownCycle, validate, validateTree

Methods inherited from class java.awt.Component
action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, disable, disableEvents, dispatchEvent, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getAccessibleContext, getBackground, getBaseline, getBaselineResizeBehavior, getBounds, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeysEnabled, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - GCanvas
```
public GCanvas()
```
    Creates a new GCanvas that contains no objects.
- Method Detail
  - add
```
public void add(GObject gobj)
```
    Adds the graphical object to this canvas.
    
    Specified by:
    
    add in interface GContainer
    
    Parameters:
    
    gobj - The graphical object to add
  - add
```
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).
    
    Specified by:
    
    add in interface GContainer
    
    Parameters:
    
    gobj - The graphical object to add
    
    x - The new x-coordinate for the object
    
    y - The new y-coordinate for the object
  - add
```
public final void add(GObject gobj,
                      GPoint pt)
```
    Adds the graphical object to this canvas and sets its location to the specified point.
    
    Specified by:
    
    add in interface GContainer
    
    Parameters:
    
    gobj - The graphical object to add
    
    pt - A GPoint object giving the coordinates of the point
  - remove
```
public void remove(GObject gobj)
```
    Removes a graphical object from this GCanvas.
    
    Specified by:
    
    remove in interface GContainer
    
    Parameters:
    
    gobj - The graphical object to remove
  - removeAll
```
public void removeAll()
```
    Removes all graphical objects from this GCanvas.
    
    Specified by:
    
    removeAll in interface GContainer
    
    Overrides:
    
    removeAll in class java.awt.Container
  - add
```
public java.awt.Component add(java.awt.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.
    
    Overrides:
    
    add in class java.awt.Container
    
    Parameters:
    
    comp - The component to add
  - add
```
public final void add(java.awt.Component comp,
                      double x,
                      double y)
```
    Adds the component to this canvas and sets its location to the point (x, y).
    
    Parameters:
    
    comp - The component to add
    
    x - The new x-coordinate for the object
    
    y - The new y-coordinate for the object
  - add
```
public final void add(java.awt.Component comp,
                      GPoint pt)
```
    Adds the component to this canvas and sets its location to the specified point.
    
    Parameters:
    
    comp - The component to add
    
    pt - A GPoint object giving the coordinates of the point
  - remove
```
public void remove(java.awt.Component comp)
```
    Removes the component from the canvas.
    
    Overrides:
    
    remove in class java.awt.Container
    
    Parameters:
    
    comp - The component to remove
  - getElementCount
```
public int getElementCount()
```
    Returns the number of graphical objects stored in this GCanvas.
    
    Specified by:
    
    getElementCount in interface GContainer
    
    Returns:
    
    The number of graphical objects in this GCanvas
  - getElement
```
public GObject getElement(int index)
```
    Returns the graphical object at the specified index, numbering from back to front in the the z dimension.
    
    Specified by:
    
    getElement in interface GContainer
    
    Parameters:
    
    index - The index of the component to return
    
    Returns:
    
    The graphical object at the specified index
  - getElementAt
```
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.
    
    Specified by:
    
    getElementAt in interface GContainer
    
    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
  - getElementAt
```
public final GObject getElementAt(GPoint pt)
```
    Returns the topmost graphical object that contains the specified point, or null if no such object exists.
    
    Specified by:
    
    getElementAt in interface GContainer
    
    Parameters:
    
    pt - The coordinates being tested
    
    Returns:
    
    The graphical object at the specified location, or null if no such object exists
  - iterator
```
public java.util.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.
    
    Returns:
    
    An Iterator ranging over the elements of the container from back to front
  - iterator
```
public java.util.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(); )
 
 
```
    Returns:
    
    An Iterator ranging over the elements of the container in the specified direction
  - setOpaque
```
public void setOpaque(boolean flag)
```
    Sets a flag indicating whether this canvas is opaque, which means that it obscures anything behind it. Setting this flag to false makes the GCanvas transparent, so that any other lightweight components behind it show through.
    
    Parameters:
    
    flag - true to make this canvas opaque, and false to make it transparent
  - isOpaque
```
public boolean isOpaque()
```
    Returns a boolean value indicating whether this canvas is opaque.
    
    Overrides:
    
    isOpaque in class java.awt.Component
    
    Returns:
    
    true if this canvas is opaque, and false if it is transparent
  - getWidth
```
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.
    
    Overrides:
    
    getWidth in class java.awt.Component
    
    Returns:
    
    The width of this canvas
  - getHeight
```
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.
    
    Overrides:
    
    getHeight in class java.awt.Component
    
    Returns:
    
    The height of this canvas in pixels
  - paint
```
public void paint(java.awt.Graphics g)
```
    Paints the canvas. This method is not ordinarily called by clients.
    
    Overrides:
    
    paint in class java.awt.Container
    
    Parameters:
    
    g - The graphics context into which the canvas is painted
  - update
```
public void update(java.awt.Graphics g)
```
    Updates the canvas. This method is overridden here to support transparency in the Swing style.
    
    Overrides:
    
    update in class java.awt.Container
    
    Parameters:
    
    g - The graphics context into which the canvas is painted
  - setAutoRepaintFlag
```
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.
    
    Parameters:
    
    state - true to enable auto-repaint mode, and false to disable it
  - getAutoRepaintFlag
```
public boolean getAutoRepaintFlag()
```
    Returns the current setting of the auto-repaint flag as described in setAutoRepaintFlag.
    
    Returns:
    
    true if auto-repaint mode is enabled, and false otherwise
  - setNativeArcFlag
```
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.
    
    Parameters:
    
    state - true to enable native arcs, false to use polygons
  - getNativeArcFlag
```
public boolean getNativeArcFlag()
```
    Returns the current setting of the native-arc flag as described in setNativeArcFlag.
    
    Returns:
    
    true if native arcs are enabled, and false otherwise
  - sendToFront
```
protected void sendToFront(GObject gobj)
```
    Implements the sendToFront function from the GContainer interface. Clients should not be calling this method, but the semantics of interfaces forces it to be exported.
  - sendToBack
```
protected void sendToBack(GObject gobj)
```
    Implements the sendToBack function from the GContainer interface. Clients should not be calling this method, but the semantics of interfaces forces it to be exported.
  - sendForward
```
protected void sendForward(GObject gobj)
```
    Implements the sendForward function from the GContainer interface. Clients should not be calling this method, but the semantics of interfaces forces it to be exported.
  - sendBackward
```
protected void sendBackward(GObject gobj)
```
    Implements the sendBackward function from the GContainer interface. Clients should not be calling this method, but the semantics of interfaces forces it to be exported.
  - dispatchMouseEvent
```
protected void dispatchMouseEvent(java.awt.event.MouseEvent e)
```
    Dispatches this mouse event to the uppermost graphical object for which the active point is within the object bounds.
    
    Parameters:
    
    e - The event that triggered this response
  - initOffscreenImage
```
protected void initOffscreenImage()
```
    Initializes the offscreen memory image used for double buffering.
  - conditionalRepaint
```
protected void conditionalRepaint()
```
    Repaints the canvas if auto-repaint is in effect. This method is called only by the repaint method in GObject and is not accessible outside the package.
  - updateEnabledList
```
protected void updateEnabledList()
```
    Reconstructs the enabledList list in the correct order.

Class GCanvas

Nested Class Summary

Nested classes/interfaces inherited from class java.awt.Container

Nested classes/interfaces inherited from class java.awt.Component

Field Summary

Fields inherited from class java.awt.Component

Fields inherited from interface acm.graphics.GContainer

Fields inherited from interface java.awt.image.ImageObserver

Constructor Summary

Method Summary

Methods inherited from class java.awt.Container

Methods inherited from class java.awt.Component

Methods inherited from class java.lang.Object

Constructor Detail

GCanvas

Method Detail

add

add

add

remove

removeAll

add

add

add

remove

getElementCount

getElement

getElementAt

getElementAt

iterator

iterator

setOpaque

isOpaque

getWidth

getHeight

paint

update

setAutoRepaintFlag

getAutoRepaintFlag

setNativeArcFlag

getNativeArcFlag

sendToFront

sendToBack

sendForward

sendBackward

dispatchMouseEvent

initOffscreenImage

conditionalRepaint

updateEnabledList