| JCanvas |
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typedict |
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A
JCanvas
is a convenience type for drawing much like the AWT Canvas component, but it
is implemented using the Java Swing JPanel class.
Though in many instances one could simply use the Yoix JPanel type in lieu of
a JCanvas, having a separate type for drawing is conceptually clearer and also
makes conversion from AWT to Swing scripts easier.
Yoix programs normally interact with a
JCanvas
using event handlers and by reading or writing the following fields:
| background |
The
Color
that is used to paint the background of the canvas.
Reading returns a snapshot of the current color.
Writing immediately changes the background to the new color.
Storing
NULL
in
background
is special and means use the background of the nearest component
that contains the canvas and was assigned a background color other than
NULL;
if no component qualifies the canvas uses
VM.screen.background.
| | backgroundhints |
An
int
that controls how
backgroundimage
is displayed in the canvas.
The value should be one of
SCALE_AREA,
SCALE_DEFAULT,
SCALE_FAST,
SCALE_NONE,
SCALE_REPLICATE,
SCALE_SMOOTH,
or
SCALE_TILE,
which are all defined in
yoix.image.
SCALE_NONE
places the unscaled image in the upper left corner of the canvas,
while
SCALE_TILE
(the default) tiles the entire canvas with the unscaled image.
The other values select the algorithm used to scale
backgroundimage
so it fills the entire canvas.
Reading returns the current hints.
Writing immediately repaints the canvas using the new hints to
display the background image.
| | backgroundimage |
An
Object
that should be an
Image
or
String
that identifies an image that is automatically displayed as part of the
canvas's background in a way that is controlled by the value assigned to
backgroundhints.
A
NULL
value, which is the default, means there is no image.
A
backgroundimage
that is a
String
should name a local a file or URL that contains a GIF or JPEG image.
Reading returns the current image.
Writing immediately repaints the canvas using the new image.
| | border |
An
Object
that should be a
Border,
Insets,
Number,
or
String
that describes the border that is drawn around this canvas.
A
NULL
value, which is the default, means no border.
A
border
that is an
Insets
or
Number
is handled differently than most other Swing components,
because it is used, in combination with the
insets
field, to set the extent of the highlighted border,
in units of 72 dots per inch, that is drawn around the canvas.
A
border
that is a
String
is a quick way to surround this canvas with a border that uses the
String
as its title.
Reading returns a snapshot of the current border.
Writing immediately sets the canvas's border to the new value.
| | bordercolor |
The base
Color
that is used to pick the shadow colors for the highlighted border.
The canvas's background is used when bordercolor is
NULL.
Reading returns a snapshot of the current color.
Writing immediately changes the bordercolor to the new color.
| | buttonmask |
An
int
that indicates which mouse button (or buttons) are accepted to trigger
an action when the canvas is being used as a custom button.
Acceptable value, which can be
OR'ed
together, are
BUTTON1_MASK,
BUTTON2_MASK
or
BUTTON3_MASK,
which are defined in
yoix.swing.
The default mask is
BUTTON1_MASK.
| | cursor |
An
Object
that should be an
int,
Image,
or
String
that selects the cursor shown when the pointer is over the canvas.
A
cursor
that is an
int
should be one of the cursors defined in the
yoix.awt.Cursor
dictionary.
A
cursor
that is an
Image
can describe the cursor using its
size
and
hotspot
fields and often draws it using its
paint
function.
A
cursor
that is a
String
should be the name of a cursor that is already defined in
yoix.awt.Cursor
or the name a local a file or URL that contains a GIF or JPEG image
that will be used as the cursor.
Reading returns the current cursor.
Writing immediately changes the canvas's cursor to the new value.
Storing
STANDARD_CURSOR
(the default) or
NULL
in
cursor
is special and means use the cursor assigned to the nearest component
that contains the canvas and was assigned a cursor other than
STANDARD_CURSOR;
if no component qualifies the canvas uses
DEFAULT_CURSOR.
| | doublebuffered |
An
int
that is
1
when the canvas uses double-buffering to draw itself,
0
when it does not, and starts with a default value that is
selected by Java for the canvas.
Reading returns the current double-buffering behavior.
Writing immediately sets the canvas's double-buffering behavior to the new value.
Note that double-buffering may be required when transparent components are used.
| | dragenabled |
An
int
that should be set to
1
when this canvas wants to use the automatic drag handling that Swing provides
for some components, and
0
(the default)
when it does not.
Components that do not provide automatic drag handling always return
0
when their
dragenabled
field is read, so storing
1
in
dragenabled
should only be viewed as a request for a service that may not be available.
Swing components can always take complete control of their drag and drop
handling using their
transferhandler
field or special drag and drop event handlers.
| | enabled |
An
Object
that is
1
when the canvas can respond to user input,
0
when it can not respond, and
NULL
(the default)
when the canvas inherits the value from the nearest lightweight container,
like a
JPanel,
that contains the canvas and has its
enabled
field set to something other than
NULL.
The top-level application window that contains the canvas always gets the
final say, so disabling that window always disables the canvas.
Reading returns the current state.
Writing immediately sets the canvas's state to the new value.
| | focusowner |
A read-only
int
that is non-zero when the canvas has the focus.
| | font |
The
Font,
or font name if it is a
String,
that is used as the canvas's font.
Reading returns a snapshot of the current font.
Writing immediately sets the canvas's font to the new value.
| | foreground |
The
Color
that is used as the foreground of the canvas.
Reading returns a snapshot of the current color.
Writing immediately sets the canvas's foreground to the new color.
Storing
NULL
in
foreground
is special and means use the foreground of the nearest component
that contains the canvas and was assigned a foreground color other than
NULL;
if no component qualifies the canvas uses
VM.screen.foreground.
| | graphics |
A
Graphics
object that defines properties and built-ins that are used to apply
graphics operations to this canvas.
Writing after a canvas has been created is not allowed and will result in an
invalidaccess
error.
| | layer |
An
int,
often a small number between 0 and 99,
that identifies the depth of this canvas when it is added to a
JLayeredPane
or
JDesktopPane.
Components assigned to lower numbered layers are drawn before
the components in higher numbered layers.
Writing immediately changes the canvas's layer, which usually means the
JLayeredPane
or
JDesktopPane
that contains the canvas will be repainted.
| | location |
A
Point
that determines the location of the canvas
in a coordinate system that has its origin at the upper left corner
of the container closest to the canvas (in the component hierarchy)
that actually contains it, positive x to the right, positive y down,
and a resolution of 72 dots per inch.
Reading returns a snapshot of the current location.
Writing is allowed, but layout managers usually get the final say, so setting
location
should be viewed as a request that may not be honored.
| | nextfocus |
An
Object
that is the component that receives the focus after this canvas
when the focus traverses from one component to the next
(usually by means of the keyboard
TAB
character).
A
NULL
value indicates that the default Java focus traversal is in effect.
Reading returns the value last stored.
Writing immediately sets the new focus traversal behavior.
| | opaque |
An
Object
that is
1
when the canvas is opaque,
0
when it is transparent, and
NULL
(the default)
when the canvas inherits the value from the nearest component that
contains the canvas and has its
opaque
field set to something other than
NULL.
| | paint([Rectangle rect]) |
A
Function
that is called, if it is not
NULL,
whenever the canvas needs to be painted.
The optional
rect
argument describes the rectangle that needs repainting in the
coordinate system specified by
graphics.CTM,
which by default has its origin at the canvas's upper left corner,
positive x to the right, positive y down, and a resolution of 72 dots per inch.
| | popup |
A
JPopupMenu
that is associated with the canvas.
Reading returns the current popup menu.
Writing immediately shows the popup menu at the point in the canvas's coordinate
system specified by the popup menu's
location
field, assuming of course that the canvas is showing on the screen.
Storing
TRUE
in the popup menu's
visible
field, which was added in release 1.2.0, is an easy way to show the
popup menu that currently belongs to the canvas.
| | preferredsize |
A
Dimension
that is used by layout managers when they need to know the canvas's
preferred size in units of 72 dots per inch.
A
NULL
value means the canvas has no preference.
A non-positive height or width is allowed and simply means the canvas
has no preference for that dimension.
Reading returns the current preferred size.
Writing changes the preferred size and immediately notifies
root.layoutmanager,
which means the components contained in
root
may be repositioned and resized.
| | repaint() |
A
Builtin
that tells the canvas to completely repaint itself,
which means the background is regenerated and then the canvas's
paint
function is called.
Obviously
repaint
should not be called, either directly or indirectly, from the canvas's
paint
function, however
erasedrawable
is safe because it does not trigger a
paint
call.
| | requestfocus |
An
int
that can be used to request or transfer the keyboard focus.
Storing a non-zero value in
requestfocus
tries to get the focus.
Storing
0
tries to transfer the focus.
Reading
requestfocus
does not currently return any useful information.
| | requestfocusenabled |
An
int
that is
1
(the default)
when actions, like mouse clicks or changes to the
requestfocus
field, can steal the keyboard focus and
0
when they can not.
Note that this field does not affect acceptance of the keyboard focus
during normal focus traversal.
Reading returns the current state.
Writing immediately sets the canvas's state to the new value.
| | root |
An
Object
that is automatically updated by the interpreter's layout machinery
so it is always the top-level object that contains the canvas.
For example, put a canvas in a panel and
root
will be set to that panel;
add the panel to a frame and the canvas's
root
field will be set to that frame.
A canvas's event handlers can use
root
when they need to interact with the other components in the container.
| | showing |
A read-only
int
that is non-zero when the canvas is showing on the screen.
| | size |
A
Dimension
that determines the size of the canvas
in units of 72 dots per inch.
Reading returns a snapshot of the current size.
Writing is allowed, but layout managers usually get the final say, so setting
size
should be viewed as a request that may not be honored.
| | state |
An
int
that controls how the border of the canvas, if there is one,
is drawn.
When state is
0
the left and top parts of the border are drawn in a brighter
color than the right and bottom parts, which makes it look like
the interior of the canvas is raised.
The border colors are reversed when state is
1,
which makes it look like the interior of the canvas is depressed.
| | sticky |
An
int
which is 1 when a change of state from 0 to 1 caused by a mouse press will not
reset to 0 at mouse release.
This feature provides a way to simulate check box or radio button behavior
with a
JCanvas.
| | tag |
A
String
used to identify the canvas that is either supplied when
the canvas is declared, or automatically generated otherwise.
Add a canvas to a container, like a
JFrame
or
JPanel,
and the interpreter's layout machinery updates the
root
field so it points at the top-level container and then adds the canvas, as
tag,
to the
root.components
dictionary.
| | tooltiptext |
A
String
of characters that is displayed in a tightly sized pop-up window that
appears near the cursor whenever the cursor lingers over the canvas.
Setting this value to
NULL
(the default)
disables the tooltip mechanism.
Reading returns the current tooltip text.
Writing immediately sets the new tooltip text.
| | transferhandler |
An
Object
that should be a
TransferHandler
or
String
that determines how the canvas handles data transfer operations
like drag and drop.
A value that is a
String
but not
""
means the field named by the
String
should be used as the source and sink of the data that is transferred by
the canvas.
The result is the same as assigning the
String
to the
property
field in a
TransferHandler
and then assigning that
TransferHandler
to
transferhandler.
The empty
String
""
is special and refers to the
TransferHandler
that Swing uses for automatic drag handling, if there is one.
Swing components that provide automatic drag handling start out with a
transferhandler
field that is not
NULL,
but the automatic drag handling is not enabled until
1
is stored in
dragenabled.
Swing components that provide their own drag and drop event handlers
currently must store
NULL
in
transferhandler
before those event handlers will start working.
| | visible |
An
int
that is
1
when the canvas is visible, and
0
otherwise.
Reading returns the current visibility.
Writing immediately sets the canvas's visibility to the new state.
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Several permanent fields have not been documented and should not be
used in Yoix applications.
Event handlers are functions that must be added to a canvas when it is
declared.
The handlers that work with canvases are listed below;
the names should be familiar if you have done some Java programming.
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| Event Handlers: |
actionPerformed,
componentHidden,
componentMoved,
componentResized,
componentShown,
dragDropEnd,
dragEnter,
dragExit,
dragGestureRecognized,
dragMouseMoved,
dragOver,
drop,
dropActionChanged,
focusGained,
focusLost,
invocationRun,
itemStateChanged,
keyPressed,
keyReleased,
keyTyped,
mouseClicked,
mouseDragged,
mouseEntered,
mouseExited,
mouseMoved,
mousePressed,
mouseReleased,
mouseWheelMoved
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| Example: |
The program,
import yoix.*.*;
JFrame f = {
FlowLayout layoutmanager = {
int hgap = 72/4;
int vgap = 72;
};
Array layout = {
new JCanvas {
Color background = {double red = .5;};
int border = 72/12;
int state = FALSE;
Dimension size = {
int height = 72;
int width = 2*72;
};
},
new JCanvas {
Color background = {double green = .5;};
int border = 72/12;
int state = TRUE;
Dimension size = {
int height = 72;
int width = 72;
};
},
new JCanvas {
Color background = Color.blue;
Dimension preferredsize = {
int height = 36;
int width = 72;
};
},
};
};
f.visible = TRUE;
sleep(5);
f.visible = FALSE;
shows three canvases in a frame, but only for a few seconds.
The next program,
import yoix.*.*;
final double SHADOW = 72.0/36;
Image att = {
String source = "http://www.yoix.org/imgs/ATTlogo.gif";
};
JCanvas c = {
double border = SHADOW;
Color background = Color.gray;
Image backgroundimage = att;
int backgroundhints = SCALE_DEFAULT;
int state = FALSE;
Dimension size = {
double width = att.size.width + 2*SHADOW;
double height = att.size.height + 2*SHADOW;
};
actionPerformed(ActionEvent e) {
printf("URL=%s\n", att.source);
}
};
JFrame f = {
FlowLayout layoutmanager = {
int vgap = 72;
};
Array layout = {c};
};
f.visible = TRUE;
sleep(5);
exit(0);
shows how to build a custom button out of a canvas that displays
an image rather than a text string.
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| See Also: |
BevelBorder,
Border,
EmptyBorder,
EtchedBorder,
invokeLater,
JButton,
JCheckBox,
JCheckBoxMenuItem,
JChoice,
JColorChooser,
JComboBox,
JDesktopPane,
JDialog,
JFileChooser,
JFileDialog,
JFrame,
JInternalFrame,
JLabel,
JLayeredPane,
JList,
JMenu,
JMenuBar,
JMenuItem,
JPanel,
JPasswordField,
JPopupMenu,
JProgressBar,
JRadioButton,
JRadioButtonMenuItem,
JScrollBar,
JScrollPane,
JSeparator,
JSlider,
JSplitPane,
JTabbedPane,
JTable,
JTextArea,
JTextCanvas,
JTextField,
JTextPane,
JTextTerm,
JToggleButton,
JToolBar,
JTree,
JWindow,
LineBorder,
MatteBorder,
postEvent,
SoftBevelBorder,
TransferHandler
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Yoix is a registered trademark of AT&T Intellectual Property.
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