canvas(n)
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NAME
canvas - Create and manipulate canvas widgets
SYNOPSIS
canvas pathName ?options?
STANDARD OPTIONS
-background -highlightthickness -insertwidth-takefocus
-borderwidth -insertbackground -relief-xscrollcommand
-cursor -insertborderwidth -selectbackground-yscrollcommand
-highlightbackground -insertofftime -selectborderwidth
-highlightcolor -insertontime -selectforeground
See the options manual entry for details on the standard
options.
WIDGET-SPECIFIC OPTIONS
Command-Line Name:-closeenough
Database Name: closeEnough
Database Class: CloseEnough
Specifies a floating-point value indicating how
close the mouse cursor must be to an item before it
is considered to be ``inside'' the item. Defaults
to 1.0.
Command-Line Name:-confine
Database Name: confine
Database Class: Confine
Specifies a boolean value that indicates whether or
not it should be allowable to set the canvas's view
outside the region defined by the scrollRegion
argument. Defaults to true, which means that the
view will be constrained within the scroll region.
Command-Line Name:-height
Database Name: height
Database Class: Height
Specifies a desired window height that the canvas
widget should request from its geometry manager.
The value may be specified in any of the forms
described in the COORDINATES section below.
Command-Line Name:-scrollregion
Database Name: scrollRegion
Database Class: ScrollRegion
Specifies a list with four coordinates describing
the left, top, right, and bottom coordinates of a
rectangular region. This region is used for
scrolling purposes and is considered to be the
boundary of the information in the canvas. Each of
the coordinates may be specified in any of the
forms given in the COORDINATES section below.
Command-Line Name:-width
Database Name: width
Database Class: width
Specifies a desired window width that the canvas
widget should request from its geometry manager.
The value may be specified in any of the forms
described in the COORDINATES section below.
Command-Line Name:-xscrollincrement
Database Name: xScrollIncrement
Database Class: ScrollIncrement
Specifies an increment for horizontal scrolling, in
any of the usual forms permitted for screen dis-
tances. If the value of this option is greater
than zero, the horizontal view in the window will
be constrained so that the canvas x coordinate at
the left edge of the window is always an even mul-
tiple of xScrollIncrement; furthermore, the units
for scrolling (e.g., the change in view when the
left and right arrows of a scrollbar are selected)
will also be xScrollIncrement. If the value of
this option is less than or equal to zero, then
horizontal scrolling is unconstrained.
Command-Line Name:-yscrollincrement
Database Name: yScrollIncrement
Database Class: ScrollIncrement
Specifies an increment for vertical scrolling, in
any of the usual forms permitted for screen dis-
tances. If the value of this option is greater
than zero, the vertical view in the window will be
constrained so that the canvas y coordinate at the
top edge of the window is always an even multiple
of yScrollIncrement; furthermore, the units for
scrolling (e.g., the change in view when the top
and bottom arrows of a scrollbar are selected) will
also be yScrollIncrement. If the value of this
option is less than or equal to zero, then vertical
scrolling is unconstrained.
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INTRODUCTION
The canvas command creates a new window (given by the
pathName argument) and makes it into a canvas widget.
Additional options, described above, may be specified on
the command line or in the option database to configure
aspects of the canvas such as its colors and 3-D relief.
The canvas command returns its pathName argument. At the
time this command is invoked, there must not exist a win-
dow named pathName, but pathName's parent must exist.
Canvas widgets implement structured graphics. A canvas
displays any number of items, which may be things like
rectangles, circles, lines, and text. Items may be manip-
ulated (e.g. moved or re-colored) and commands may be
associated with items in much the same way that the bind
command allows commands to be bound to widgets. For exam-
ple, a particular command may be associated with the <But-
ton-1> event so that the command is invoked whenever but-
ton 1 is pressed with the mouse cursor over an item. This
means that items in a canvas can have behaviors defined by
the Tcl scripts bound to them.
DISPLAY LIST
The items in a canvas are ordered for purposes of display,
with the first item in the display list being displayed
first, followed by the next item in the list, and so on.
Items later in the display list obscure those that are
earlier in the display list and are sometimes referred to
as being ``on top'' of earlier items. When a new item is
created it is placed at the end of the display list, on
top of everything else. Widget commands may be used to
re-arrange the order of the display list.
Window items are an exception to the above rules. The
underlying window systems require them always to be drawn
on top of other items. In addition, the stacking order of
window items is not affected by any of the canvas widget
commands; you must use the raise and lower Tk commands
instead.
ITEM IDS AND TAGS
Items in a canvas widget may be named in either of two
ways: by id or by tag. Each item has a unique identifying
number which is assigned to that item when it is created.
The id of an item never changes and id numbers are never
re-used within the lifetime of a canvas widget.
Each item may also have any number of tags associated with
it. A tag is just a string of characters, and it may take
any form except that of an integer. For example, ``x123''
is OK but ``123'' isn't. The same tag may be associated
with many different items. This is commonly done to group
items in various interesting ways; for example, all
selected items might be given the tag ``selected''.
The tag all is implicitly associated with every item in
the canvas; it may be used to invoke operations on all
the items in the canvas.
The tag current is managed automatically by Tk; it applies
to the current item, which is the topmost item whose drawn
area covers the position of the mouse cursor. If the
mouse is not in the canvas widget or is not over an item,
then no item has the current tag.
When specifying items in canvas widget commands, if the
specifier is an integer then it is assumed to refer to the
single item with that id. If the specifier is not an
integer, then it is assumed to refer to all of the items
in the canvas that have a tag matching the specifier. The
symbol tagOrId is used below to indicate that an argument
specifies either an id that selects a single item or a tag
that selects zero or more items. Some widget commands
only operate on a single item at a time; if tagOrId is
specified in a way that names multiple items, then the
normal behavior is for the command to use the first (low-
est) of these items in the display list that is suitable
for the command. Exceptions are noted in the widget com-
mand descriptions below.
COORDINATES
All coordinates related to canvases are stored as float-
ing-point numbers. Coordinates and distances are speci-
fied in screen units, which are floating-point numbers
optionally followed by one of several letters. If no let-
ter is supplied then the distance is in pixels. If the
letter is m then the distance is in millimeters on the
screen; if it is c then the distance is in centimeters; i
means inches, and p means printers points (1/72 inch).
Larger y-coordinates refer to points lower on the screen;
larger x-coordinates refer to points farther to the right.
TRANSFORMATIONS
Normally the origin of the canvas coordinate system is at
the upper-left corner of the window containing the canvas.
It is possible to adjust the origin of the canvas coordi-
nate system relative to the origin of the window using the
xview and yview widget commands; this is typically used
for scrolling. Canvases do not support scaling or rota-
tion of the canvas coordinate system relative to the win-
dow coordinate system.
Individual items may be moved or scaled using widget com-
mands described below, but they may not be rotated.
INDICES
Text items support the notion of an index for identifying
particular positions within the item. Indices are used
for commands such as inserting text, deleting a range of
characters, and setting the insertion cursor position. An
index may be specified in any of a number of ways, and
different types of items may support different forms for
specifying indices. Text items support the following
forms for an index; if you define new types of text-like
items, it would be advisable to support as many of these
forms as practical. Note that it is possible to refer to
the character just after the last one in the text item;
this is necessary for such tasks as inserting new text at
the end of the item.
number A decimal number giving the position of the
desired character within the text item. 0
refers to the first character, 1 to the next
character, and so on. A number less than 0 is
treated as if it were zero, and a number greater
than the length of the text item is treated as
if it were equal to the length of the text item.
end Refers to the character just after the last one
in the item (same as the number of characters in
the item).
insert Refers to the character just before which the
insertion cursor is drawn in this item.
sel.first Refers to the first selected character in the
item. If the selection isn't in this item then
this form is illegal.
sel.last Refers to the last selected character in the
item. If the selection isn't in this item then
this form is illegal.
@x,y Refers to the character at the point given by x
and y, where x and y are specified in the coor-
dinate system of the canvas. If x and y lie
outside the coordinates covered by the text
item, then they refer to the first or last char-
acter in the line that is closest to the given
point.
WIDGET COMMAND
The canvas command creates a new Tcl command whose name is
pathName. This command may be used to invoke various
operations on the widget. It has the following general
form:
pathName option ?arg arg ...?
Option and the args determine the exact behavior of the
command. The following widget commands are possible for
canvas widgets:
pathName addtag tag searchSpec ?arg arg ...?
For each item that meets the constraints specified
by searchSpec and the args, add tag to the list of
tags associated with the item if it isn't already
present on that list. It is possible that no items
will satisfy the constraints given by searchSpec
and args, in which case the command has no effect.
This command returns an empty string as result.
SearchSpec and arg's may take any of the following
forms:
above tagOrId
Selects the item just after (above) the one
given by tagOrId in the display list. If
tagOrId denotes more than one item, then the
last (topmost) of these items in the display
list is used.
all Selects all the items in the canvas.
below tagOrId
Selects the item just before (below) the one
given by tagOrId in the display list. If
tagOrId denotes more than one item, then the
first (lowest) of these items in the display
list is used.
closest x y ?halo? ?start?
Selects the item closest to the point given
by x and y. If more than one item is at the
same closest distance (e.g. two items over-
lap the point), then the top-most of these
items (the last one in the display list) is
used. If halo is specified, then it must be
a non-negative value. Any item closer than
halo to the point is considered to overlap
it. The start argument may be used to step
circularly through all the closest items.
If start is specified, it names an item
using a tag or id (if by tag, it selects the
first item in the display list with the
given tag). Instead of selecting the top-
most closest item, this form will select the
topmost closest item that is below start in
the display list; if no such item exists,
then the selection behaves as if the start
argument had not been specified.
enclosed x1 y1 x2 y2
Selects all the items completely enclosed
within the rectangular region given by x1,
y1, x2, and y2. X1 must be no greater then
x2 and y1 must be no greater than y2.
overlapping x1 y1 x2 y2
Selects all the items that overlap or are
enclosed within the rectangular region given
by x1, y1, x2, and y2. X1 must be no
greater then x2 and y1 must be no greater
than y2.
withtag tagOrId
Selects all the items given by tagOrId.
pathName bbox tagOrId ?tagOrId tagOrId ...?
Returns a list with four elements giving an approx-
imate bounding box for all the items named by the
tagOrId arguments. The list has the form ``x1 y1
x2 y2'' such that the drawn areas of all the named
elements are within the region bounded by x1 on the
left, x2 on the right, y1 on the top, and y2 on the
bottom. The return value may overestimate the
actual bounding box by a few pixels. If no items
match any of the tagOrId arguments or if the match-
ing items have empty bounding boxes (i.e. they have
nothing to display) then an empty string is
returned.
pathName bind tagOrId ?sequence? ?command?
This command associates command with all the items
given by tagOrId such that whenever the event
sequence given by sequence occurs for one of the
items the command will be invoked. This widget
command is similar to the bind command except that
it operates on items in a canvas rather than entire
widgets. See the bind manual entry for complete
details on the syntax of sequence and the substitu-
tions performed on command before invoking it. If
all arguments are specified then a new binding is
created, replacing any existing binding for the
same sequence and tagOrId (if the first character
of command is ``+'' then command augments an exist-
ing binding rather than replacing it). In this
case the return value is an empty string. If com-
mand is omitted then the command returns the com-
mand associated with tagOrId and sequence (an error
occurs if there is no such binding). If both com-
mand and sequence are omitted then the command
returns a list of all the sequences for which bind-
ings have been defined for tagOrId.
The only events for which bindings may be specified |
are those related to the mouse and keyboard (such |
as Enter, Leave, ButtonPress, Motion, and KeyPress) |
or virtual events. The handling of events in can- |
vases uses the current item defined in ITEM IDS AND |
TAGS above. Enter and Leave events trigger for an |
item when it becomes the current item or ceases to |
be the current item; note that these events are |
different than Enter and Leave events for windows. |
Mouse-related events are directed to the current |
item, if any. Keyboard-related events are directed |
to the focus item, if any (see the focus widget |
command below for more on this). If a virtual |
event is used in a binding, that binding can trig- |
ger only if the virtual event is defined by an |
underlying mouse-related or keyboard-related event.
It is possible for multiple bindings to match a
particular event. This could occur, for example,
if one binding is associated with the item's id and
another is associated with one of the item's tags.
When this occurs, all of the matching bindings are
invoked. A binding associated with the all tag is
invoked first, followed by one binding for each of
the item's tags (in order), followed by a binding
associated with the item's id. If there are multi-
ple matching bindings for a single tag, then only
the most specific binding is invoked. A continue
command in a binding script terminates that script,
and a break command terminates that script and
skips any remaining scripts for the event, just as
for the bind command.
If bindings have been created for a canvas window
using the bind command, then they are invoked in
addition to bindings created for the canvas's items
using the bind widget command. The bindings for
items will be invoked before any of the bindings
for the window as a whole.
pathName canvasx screenx ?gridspacing?
Given a window x-coordinate in the canvas screenx,
this command returns the canvas x-coordinate that
is displayed at that location. If gridspacing is
specified, then the canvas coordinate is rounded to
the nearest multiple of gridspacing units.
pathName canvasy screeny ?gridspacing?
Given a window y-coordinate in the canvas screeny
this command returns the canvas y-coordinate that
is displayed at that location. If gridspacing is
specified, then the canvas coordinate is rounded to
the nearest multiple of gridspacing units.
pathName cget option
Returns the current value of the configuration
option given by option. Option may have any of the
values accepted by the canvas command.
pathName configure ?option? ?value? ?option value ...?
Query or modify the configuration options of the
widget. If no option is specified, returns a list
describing all of the available options for path-
Name (see Tk_ConfigureInfo for information on the
format of this list). If option is specified with
no value, then the command returns a list describ-
ing the one named option (this list will be identi-
cal to the corresponding sublist of the value
returned if no option is specified). If one or
more option-value pairs are specified, then the
command modifies the given widget option(s) to have
the given value(s); in this case the command
returns an empty string. Option may have any of
the values accepted by the canvas command.
pathName coords tagOrId ?x0 y0 ...?
Query or modify the coordinates that define an
item. If no coordinates are specified, this com-
mand returns a list whose elements are the coordi-
nates of the item named by tagOrId. If coordinates
are specified, then they replace the current coor-
dinates for the named item. If tagOrId refers to
multiple items, then the first one in the display
list is used.
pathName create type x y ?x y ...? ?option value ...?
Create a new item in pathName of type type. The
exact format of the arguments after type depends on
type, but usually they consist of the coordinates
for one or more points, followed by specifications
for zero or more item options. See the subsections
on individual item types below for more on the syn-
tax of this command. This command returns the id
for the new item.
pathName dchars tagOrId first ?last?
For each item given by tagOrId, delete the charac-
ters in the range given by first and last, inclu-
sive. If some of the items given by tagOrId don't
support text operations, then they are ignored.
First and last are indices of characters within the
item(s) as described in INDICES above. If last is
omitted, it defaults to first. This command
returns an empty string.
pathName delete ?tagOrId tagOrId ...?
Delete each of the items given by each tagOrId, and
return an empty string.
pathName dtag tagOrId ?tagToDelete?
For each of the items given by tagOrId, delete the
tag given by tagToDelete from the list of those
associated with the item. If an item doesn't have
the tag tagToDelete then the item is unaffected by
the command. If tagToDelete is omitted then it
defaults to tagOrId. This command returns an empty
string.
pathName find searchCommand ?arg arg ...?
This command returns a list consisting of all the
items that meet the constraints specified by
searchCommand and arg's. SearchCommand and args
have any of the forms accepted by the addtag com-
mand. The items are returned in stacking order,
with the lowest item first.
pathName focus ?tagOrId?
Set the keyboard focus for the canvas widget to the
item given by tagOrId. If tagOrId refers to sev-
eral items, then the focus is set to the first such
item in the display list that supports the inser-
tion cursor. If tagOrId doesn't refer to any
items, or if none of them support the insertion
cursor, then the focus isn't changed. If tagOrId
is an empty string, then the focus item is reset so
that no item has the focus. If tagOrId is not
specified then the command returns the id for the
item that currently has the focus, or an empty
string if no item has the focus.
Once the focus has been set to an item, the item
will display the insertion cursor and all keyboard
events will be directed to that item. The focus
item within a canvas and the focus window on the
screen (set with the focus command) are totally
independent: a given item doesn't actually have the
input focus unless (a) its canvas is the focus win-
dow and (b) the item is the focus item within the
canvas. In most cases it is advisable to follow
the focus widget command with the focus command to
set the focus window to the canvas (if it wasn't
there already).
pathName gettags tagOrId
Return a list whose elements are the tags associ-
ated with the item given by tagOrId. If tagOrId
refers to more than one item, then the tags are
returned from the first such item in the display
list. If tagOrId doesn't refer to any items, or if
the item contains no tags, then an empty string is
returned.
pathName icursor tagOrId index
Set the position of the insertion cursor for the
item(s) given by tagOrId to just before the charac-
ter whose position is given by index. If some or
all of the items given by tagOrId don't support an
insertion cursor then this command has no effect on
them. See INDICES above for a description of the
legal forms for index. Note: the insertion cursor
is only displayed in an item if that item currently
has the keyboard focus (see the widget command
focus, below), but the cursor position may be set
even when the item doesn't have the focus. This
command returns an empty string.
pathName index tagOrId index
This command returns a decimal string giving the
numerical index within tagOrId corresponding to
index. Index gives a textual description of the
desired position as described in INDICES above.
The return value is guaranteed to lie between 0 and
the number of characters within the item, inclu-
sive. If tagOrId refers to multiple items, then
the index is processed in the first of these items
that supports indexing operations (in display list
order).
pathName insert tagOrId beforeThis string
For each of the items given by tagOrId, if the item
supports text insertion then string is inserted
into the item's text just before the character
whose index is beforeThis. See INDICES above for
information about the forms allowed for beforeThis.
This command returns an empty string.
pathName itemcget tagOrId option
Returns the current value of the configuration
option for the item given by tagOrId whose name is
option. This command is similar to the cget widget
command except that it applies to a particular item
rather than the widget as a whole. Option may have
any of the values accepted by the create widget
command when the item was created. If tagOrId is a
tag that refers to more than one item, the first
(lowest) such item is used.
pathName itemconfigure tagOrId ?option? ?value? ?option
value ...?
This command is similar to the configure widget
command except that it modifies item-specific
options for the items given by tagOrId instead of
modifying options for the overall canvas widget.
If no option is specified, returns a list describ-
ing all of the available options for the first item
given by tagOrId (see Tk_ConfigureInfo for informa-
tion on the format of this list). If option is
specified with no value, then the command returns a
list describing the one named option (this list
will be identical to the corresponding sublist of
the value returned if no option is specified). If
one or more option-value pairs are specified, then
the command modifies the given widget option(s) to
have the given value(s) in each of the items given
by tagOrId; in this case the command returns an
empty string. The options and values are the same
as those permissible in the create widget command
when the item(s) were created; see the sections
describing individual item types below for details
on the legal options.
pathName lower tagOrId ?belowThis?
Move all of the items given by tagOrId to a new
position in the display list just before the item
given by belowThis. If tagOrId refers to more than
one item then all are moved but the relative order
of the moved items will not be changed. BelowThis
is a tag or id; if it refers to more than one item
then the first (lowest) of these items in the dis-
play list is used as the destination location for
the moved items. Note: this command has no effect
on window items. Window items always obscure other
item types, and the stacking order of window items
is determined by the raise and lower commands, not
the raise and lower widget commands for canvases.
This command returns an empty string.
pathName move tagOrId xAmount yAmount
Move each of the items given by tagOrId in the can-
vas coordinate space by adding xAmount to the x-
coordinate of each point associated with the item
and yAmount to the y-coordinate of each point asso-
ciated with the item. This command returns an
empty string.
pathName postscript ?option value option value ...?
Generate a Postscript representation for part or
all of the canvas. If the -file option is speci-
fied then the Postscript is written to a file and
an empty string is returned; otherwise the
Postscript is returned as the result of the com-
mand. If the interpreter that owns the canvas is |
marked as safe, the operation will fail because |
safe interpreters are not allowed to write files. |
If the -channel option is specified, the argument |
denotes the name of a channel already opened for |
writing. The Postscript is written to that channel, |
and the channel is left open for further writing at |
the end of the operation. The Postscript is cre-
ated in Encapsulated Postscript form using version
3.0 of the Document Structuring Conventions. Note:
by default Postscript is only generated for infor-
mation that appears in the canvas's window on the
screen. If the canvas is freshly created it may
still have its initial size of 1x1 pixel so nothing
will appear in the Postscript. To get around this
problem either invoke the "update" command to wait
for the canvas window to reach its final size, or
else use the -width and -height options to specify
the area of the canvas to print. The option-value
argument pairs provide additional information to
control the generation of Postscript. The follow-
ing options are supported:
-colormap varName
VarName must be the name of an array vari-
able that specifies a color mapping to use
in the Postscript. Each element of varName
must consist of Postscript code to set a
particular color value (e.g. ``1.0 1.0 0.0
setrgbcolor''). When outputting color
information in the Postscript, Tk checks to
see if there is an element of varName with
the same name as the color. If so, Tk uses
the value of the element as the Postscript
command to set the color. If this option
hasn't been specified, or if there isn't an
entry in varName for a given color, then Tk
uses the red, green, and blue intensities
from the X color.
-colormode mode
Specifies how to output color information.
Mode must be either color (for full color
output), gray (convert all colors to their
gray-scale equivalents) or mono (convert all
colors to black or white).
-file fileName
Specifies the name of the file in which to
write the Postscript. If this option isn't
specified then the Postscript is returned as
the result of the command instead of being
written to a file.
-fontmap varName
VarName must be the name of an array vari-
able that specifies a font mapping to use in
the Postscript. Each element of varName
must consist of a Tcl list with two ele-
ments, which are the name and point size of
a Postscript font. When outputting
Postscript commands for a particular font,
Tk checks to see if varName contains an ele-
ment with the same name as the font. If
there is such an element, then the font
information contained in that element is
used in the Postscript. Otherwise Tk
attempts to guess what Postscript font to
use. Tk's guesses generally only work for
well-known fonts such as Times and Helvetica
and Courier, and only if the X font name
does not omit any dashes up through the
point size. For example,
-*-Courier-Bold-R-Normal--*-120-* will work
but *Courier-Bold-R-Normal*120* will not;
Tk needs the dashes to parse the font name).
-height size
Specifies the height of the area of the can-
vas to print. Defaults to the height of the
canvas window.
-pageanchor anchor
Specifies which point of the printed area of
the canvas should appear over the position-
ing point on the page (which is given by the
-pagex and -pagey options). For example,
-pageanchor n means that the top center of
the area of the canvas being printed (as it
appears in the canvas window) should be over
the positioning point. Defaults to center.
-pageheight size
Specifies that the Postscript should be
scaled in both x and y so that the printed
area is size high on the Postscript page.
Size consists of a floating-point number
followed by c for centimeters, i for inches,
m for millimeters, or p or nothing for
printer's points (1/72 inch). Defaults to
the height of the printed area on the
screen. If both -pageheight and -pagewidth
are specified then the scale factor from
-pagewidth is used (non-uniform scaling is
not implemented).
-pagewidth size
Specifies that the Postscript should be
scaled in both x and y so that the printed
area is size wide on the Postscript page.
Size has the same form as for -pageheight.
Defaults to the width of the printed area on
the screen. If both -pageheight and
-pagewidth are specified then the scale fac-
tor from -pagewidth is used (non-uniform
scaling is not implemented).
-pagex position
Position gives the x-coordinate of the posi-
tioning point on the Postscript page, using
any of the forms allowed for -pageheight.
Used in conjunction with the -pagey and
-pageanchor options to determine where the
printed area appears on the Postscript page.
Defaults to the center of the page.
-pagey position
Position gives the y-coordinate of the posi-
tioning point on the Postscript page, using
any of the forms allowed for -pageheight.
Used in conjunction with the -pagex and
-pageanchor options to determine where the
printed area appears on the Postscript page.
Defaults to the center of the page.
-rotate boolean
Boolean specifies whether the printed area
is to be rotated 90 degrees. In non-rotated
output the x-axis of the printed area runs
along the short dimension of the page
(``portrait'' orientation); in rotated out-
put the x-axis runs along the long dimension
of the page (``landscape'' orientation).
Defaults to non-rotated.
-width size
Specifies the width of the area of the can-
vas to print. Defaults to the width of the
canvas window.
-x position
Specifies the x-coordinate of the left edge
of the area of the canvas that is to be
printed, in canvas coordinates, not window
coordinates. Defaults to the coordinate of
the left edge of the window.
-y position
Specifies the y-coordinate of the top edge
of the area of the canvas that is to be
printed, in canvas coordinates, not window
coordinates. Defaults to the coordinate of
the top edge of the window.
pathName raise tagOrId ?aboveThis?
Move all of the items given by tagOrId to a new
position in the display list just after the item
given by aboveThis. If tagOrId refers to more than
one item then all are moved but the relative order
of the moved items will not be changed. AboveThis
is a tag or id; if it refers to more than one item
then the last (topmost) of these items in the dis-
play list is used as the destination location for
the moved items. Note: this command has no effect
on window items. Window items always obscure other
item types, and the stacking order of window items
is determined by the raise and lower commands, not
the raise and lower widget commands for canvases.
This command returns an empty string.
pathName scale tagOrId xOrigin yOrigin xScale yScale
Rescale all of the items given by tagOrId in canvas
coordinate space. XOrigin and yOrigin identify the
origin for the scaling operation and xScale and
yScale identify the scale factors for x- and y-
coordinates, respectively (a scale factor of 1.0
implies no change to that coordinate). For each of
the points defining each item, the x-coordinate is
adjusted to change the distance from xOrigin by a
factor of xScale. Similarly, each y-coordinate is
adjusted to change the distance from yOrigin by a
factor of yScale. This command returns an empty
string.
pathName scan option args
This command is used to implement scanning on can-
vases. It has two forms, depending on option:
pathName scan mark x y
Records x and y and the canvas's current
view; used in conjunction with later scan
dragto commands. Typically this command is
associated with a mouse button press in the
widget and x and y are the coordinates of
the mouse. It returns an empty string.
pathName scan dragto x y.
This command computes the difference between
its x and y arguments (which are typically
mouse coordinates) and the x and y arguments
to the last scan mark command for the wid-
get. It then adjusts the view by 10 times
the difference in coordinates. This command
is typically associated with mouse motion
events in the widget, to produce the effect
of dragging the canvas at high speed through
its window. The return value is an empty
string.
pathName select option ?tagOrId arg?
Manipulates the selection in one of several ways,
depending on option. The command may take any of
the forms described below. In all of the descrip-
tions below, tagOrId must refer to an item that
supports indexing and selection; if it refers to
multiple items then the first of these that sup-
ports indexing and the selection is used. Index
gives a textual description of a position within
tagOrId, as described in INDICES above.
pathName select adjust tagOrId index
Locate the end of the selection in tagOrId
nearest to the character given by index, and
adjust that end of the selection to be at
index (i.e. including but not going beyond
index). The other end of the selection is
made the anchor point for future select to
commands. If the selection isn't currently
in tagOrId then this command behaves the
same as the select to widget command.
Returns an empty string.
pathName select clear
Clear the selection if it is in this widget.
If the selection isn't in this widget then
the command has no effect. Returns an empty
string.
pathName select from tagOrId index
Set the selection anchor point for the wid-
get to be just before the character given by
index in the item given by tagOrId. This
command doesn't change the selection; it
just sets the fixed end of the selection for
future select to commands. Returns an empty
string.
pathName select item
Returns the id of the selected item, if the
selection is in an item in this canvas. If
the selection is not in this canvas then an
empty string is returned.
pathName select to tagOrId index
Set the selection to consist of those char-
acters of tagOrId between the selection
anchor point and index. The new selection
will include the character given by index;
it will include the character given by the
anchor point only if index is greater than
or equal to the anchor point. The anchor
point is determined by the most recent
select adjust or select from command for
this widget. If the selection anchor point
for the widget isn't currently in tagOrId,
then it is set to the same character given
by index. Returns an empty string.
pathName type tagOrId
Returns the type of the item given by tagOrId, such
as rectangle or text. If tagOrId refers to more
than one item, then the type of the first item in
the display list is returned. If tagOrId doesn't
refer to any items at all then an empty string is
returned.
pathName xview ?args?
This command is used to query and change the hori-
zontal position of the information displayed in the
canvas's window. It can take any of the following
forms:
pathName xview
Returns a list containing two elements.
Each element is a real fraction between 0
and 1; together they describe the horizon-
tal span that is visible in the window. For
example, if the first element is .2 and the
second element is .6, 20% of the canvas's
area (as defined by the -scrollregion
option) is off-screen to the left, the mid-
dle 40% is visible in the window, and 40% of
the canvas is off-screen to the right.
These are the same values passed to scroll-
bars via the -xscrollcommand option.
pathName xview moveto fraction
Adjusts the view in the window so that frac-
tion of the total width of the canvas is
off-screen to the left. Fraction must be a
fraction between 0 and 1.
pathName xview scroll number what
This command shifts the view in the window
left or right according to number and what.
Number must be an integer. What must be
either units or pages or an abbreviation of
one of these. If what is units, the view
adjusts left or right in units of the
xScrollIncrement option, if it is greater
than zero, or in units of one-tenth the win-
dow's width otherwise. If what is pages
then the view adjusts in units of nine-
tenths the window's width. If number is
negative then information farther to the
left becomes visible; if it is positive
then information farther to the right
becomes visible.
pathName yview ?args?
This command is used to query and change the verti-
cal position of the information displayed in the
canvas's window. It can take any of the following
forms:
pathName yview
Returns a list containing two elements.
Each element is a real fraction between 0
and 1; together they describe the vertical
span that is visible in the window. For
example, if the first element is .6 and the
second element is 1.0, the lowest 40% of the
canvas's area (as defined by the -scrollre-
gion option) is visible in the window.
These are the same values passed to scroll-
bars via the -yscrollcommand option.
pathName yview moveto fraction
Adjusts the view in the window so that frac-
tion of the canvas's area is off-screen to
the top. Fraction is a fraction between 0
and 1.
pathName yview scroll number what
This command adjusts the view in the window
up or down according to number and what.
Number must be an integer. What must be
either units or pages. If what is units,
the view adjusts up or down in units of the
yScrollIncrement option, if it is greater
than zero, or in units of one-tenth the win-
dow's height otherwise. If what is pages
then the view adjusts in units of nine-
tenths the window's height. If number is
negative then higher information becomes
visible; if it is positive then lower
information becomes visible.
OVERVIEW OF ITEM TYPES
The sections below describe the various types of items
supported by canvas widgets. Each item type is character-
ized by two things: first, the form of the create command
used to create instances of the type; and second, a set
of configuration options for items of that type, which may
be used in the create and itemconfigure widget commands.
Most items don't support indexing or selection or the com-
mands related to them, such as index and insert. Where
items do support these facilities, it is noted explicitly
in the descriptions below (at present, only text items
provide this support).
ARC ITEMS
Items of type arc appear on the display as arc-shaped
regions. An arc is a section of an oval delimited by two
angles (specified by the -start and -extent options) and
displayed in one of several ways (specified by the -style
option). Arcs are created with widget commands of the
following form:
pathName create arc x1 y1 x2 y2 ?option value option value ...?
The arguments x1, y1, x2, and y2 give the coordinates of
two diagonally opposite corners of a rectangular region
enclosing the oval that defines the arc. After the
coordinates there may be any number of option-value pairs,
each of which sets one of the configuration options for
the item. These same option-value pairs may be used in
itemconfigure widget commands to change the item's config-
uration. The following options are supported for arcs:
-extent degrees
Specifies the size of the angular range occupied by
the arc. The arc's range extends for degrees
degrees counter-clockwise from the starting angle
given by the -start option. Degrees may be nega-
tive. If it is greater than 360 or less than -360,
then degrees modulo 360 is used as the extent.
-fill color
Fill the region of the arc with color. Color may
have any of the forms accepted by Tk_GetColor. If
color is an empty string (the default), then then
the arc will not be filled.
-outline color
Color specifies a color to use for drawing the
arc's outline; it may have any of the forms
accepted by Tk_GetColor. This option defaults to
black. If color is specified as an empty string
then no outline is drawn for the arc.
-outlinestipple bitmap
Indicates that the outline for the arc should be
drawn with a stipple pattern; bitmap specifies the
stipple pattern to use, in any of the forms
accepted by Tk_GetBitmap. If the -outline option
hasn't been specified then this option has no
effect. If bitmap is an empty string (the
default), then the outline is drawn in a solid
fashion.
-start degrees
Specifies the beginning of the angular range occu-
pied by the arc. Degrees is given in units of
degrees measured counter-clockwise from the
3-o'clock position; it may be either positive or
negative.
-stipple bitmap
Indicates that the arc should be filled in a stip-
ple pattern; bitmap specifies the stipple pattern
to use, in any of the forms accepted by Tk_Get-
Bitmap. If the -fill option hasn't been specified
then this option has no effect. If bitmap is an
empty string (the default), then filling is done in
a solid fashion.
-style type
Specifies how to draw the arc. If type is pieslice
(the default) then the arc's region is defined by a
section of the oval's perimeter plus two line seg-
ments, one between the center of the oval and each
end of the perimeter section. If type is chord
then the arc's region is defined by a section of
the oval's perimeter plus a single line segment
connecting the two end points of the perimeter sec-
tion. If type is arc then the arc's region con-
sists of a section of the perimeter alone. In this
last case the -fill option is ignored.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width outlineWidth
Specifies the width of the outline to be drawn
around the arc's region, in any of the forms
described in the COORDINATES section above. If the
-outline option has been specified as an empty
string then this option has no effect. Wide out-
lines will be drawn centered on the edges of the
arc's region. This option defaults to 1.0.
BITMAP ITEMS
Items of type bitmap appear on the display as images with
two colors, foreground and background. Bitmaps are cre-
ated with widget commands of the following form:
pathName create bitmap x y ?option value option value ...?
The arguments x and y specify the coordinates of a point
used to position the bitmap on the display (see the
-anchor option below for more information on how bitmaps
are displayed). After the coordinates there may be any
number of option-value pairs, each of which sets one of
the configuration options for the item. These same
option-value pairs may be used in itemconfigure widget
commands to change the item's configuration. The follow-
ing options are supported for bitmaps:
-anchor anchorPos
AnchorPos tells how to position the bitmap relative
to the positioning point for the item; it may have
any of the forms accepted by Tk_GetAnchor. For
example, if anchorPos is center then the bitmap is
centered on the point; if anchorPos is n then the
bitmap will be drawn so that its top center point
is at the positioning point. This option defaults
to center.
-background color
Specifies a color to use for each of the bitmap
pixels whose value is 0. Color may have any of the
forms accepted by Tk_GetColor. If this option
isn't specified, or if it is specified as an empty
string, then nothing is displayed where the bitmap
pixels are 0; this produces a transparent effect.
-bitmap bitmap
Specifies the bitmap to display in the item.
Bitmap may have any of the forms accepted by
Tk_GetBitmap.
-foreground color
Specifies a color to use for each of the bitmap
pixels whose value is 1. Color may have any of the
forms accepted by Tk_GetColor and defaults to
black.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
IMAGE ITEMS
Items of type image are used to display images on a can-
vas. Images are created with widget commands of the fol-
lowing form:
pathName create image x y ?option value option value ...?
The arguments x and y specify the coordinates of a point
used to position the image on the display (see the -anchor
option below for more information). After the coordinates
there may be any number of option-value pairs, each of
which sets one of the configuration options for the item.
These same option-value pairs may be used in itemconfigure
widget commands to change the item's configuration. The
following options are supported for images:
-anchor anchorPos
AnchorPos tells how to position the image relative
to the positioning point for the item; it may have
any of the forms accepted by Tk_GetAnchor. For
example, if anchorPos is center then the image is
centered on the point; if anchorPos is n then the
image will be drawn so that its top center point is
at the positioning point. This option defaults to
center.
-image name
Specifies the name of the image to display in the
item. This image must have been created previously
with the image create command.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item; it may be
an empty list.
LINE ITEMS
Items of type line appear on the display as one or more
connected line segments or curves. Lines are created with
widget commands of the following form:
pathName create line x1 y1... xn yn ?option value option value ...?
The arguments x1 through yn give the coordinates for a
series of two or more points that describe a series of
connected line segments. After the coordinates there may
be any number of option-value pairs, each of which sets
one of the configuration options for the item. These same
option-value pairs may be used in itemconfigure widget
commands to change the item's configuration. The follow-
ing options are supported for lines:
-arrow where
Indicates whether or not arrowheads are to be drawn
at one or both ends of the line. Where must have
one of the values none (for no arrowheads), first
(for an arrowhead at the first point of the line),
last (for an arrowhead at the last point of the
line), or both (for arrowheads at both ends). This
option defaults to none.
-arrowshape shape
This option indicates how to draw arrowheads. The
shape argument must be a list with three elements,
each specifying a distance in any of the forms
described in the COORDINATES section above. The
first element of the list gives the distance along
the line from the neck of the arrowhead to its tip.
The second element gives the distance along the
line from the trailing points of the arrowhead to
the tip, and the third element gives the distance
from the outside edge of the line to the trailing
points. If this option isn't specified then Tk
picks a ``reasonable'' shape.
-capstyle style
Specifies the ways in which caps are to be drawn at
the endpoints of the line. Style may have any of
the forms accepted by Tk_GetCapStyle (butt, pro-
jecting, or round). If this option isn't specified
then it defaults to butt. Where arrowheads are
drawn the cap style is ignored.
-fill color
Color specifies a color to use for drawing the
line; it may have any of the forms acceptable to
Tk_GetColor. It may also be an empty string, in
which case the line will be transparent. This
option defaults to black.
-joinstyle style
Specifies the ways in which joints are to be drawn
at the vertices of the line. Style may have any of
the forms accepted by Tk_GetCapStyle (bevel, miter,
or round). If this option isn't specified then it
defaults to miter. If the line only contains two
points then this option is irrelevant.
-smooth boolean
Boolean must have one of the forms accepted by
Tk_GetBoolean. It indicates whether or not the
line should be drawn as a curve. If so, the line
is rendered as a set of parabolic splines: one
spline is drawn for the first and second line seg-
ments, one for the second and third, and so on.
Straight-line segments can be generated within a
curve by duplicating the end-points of the desired
line segment.
-splinesteps number
Specifies the degree of smoothness desired for
curves: each spline will be approximated with num-
ber line segments. This option is ignored unless
the -smooth option is true.
-stipple bitmap
Indicates that the line should be filled in a stip-
ple pattern; bitmap specifies the stipple pattern
to use, in any of the forms accepted by Tk_Get-
Bitmap. If bitmap is an empty string (the
default), then filling is done in a solid fashion.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width lineWidth
LineWidth specifies the width of the line, in any
of the forms described in the COORDINATES section
above. Wide lines will be drawn centered on the
path specified by the points. If this option isn't
specified then it defaults to 1.0.
OVAL ITEMS
Items of type oval appear as circular or oval regions on
the display. Each oval may have an outline, a fill, or
both. Ovals are created with widget commands of the fol-
lowing form:
pathName create oval x1 y1 x2 y2 ?option value option value ...?
The arguments x1, y1, x2, and y2 give the coordinates of
two diagonally opposite corners of a rectangular region
enclosing the oval. The oval will include the top and
left edges of the rectangle not the lower or right edges.
If the region is square then the resulting oval is circu-
lar; otherwise it is elongated in shape. After the coor-
dinates there may be any number of option-value pairs,
each of which sets one of the configuration options for
the item. These same option-value pairs may be used in
itemconfigure widget commands to change the item's config-
uration. The following options are supported for ovals:
-fill color
Fill the area of the oval with color. Color may
have any of the forms accepted by Tk_GetColor. If
color is an empty string (the default), then then
the oval will not be filled.
-outline color
Color specifies a color to use for drawing the
oval's outline; it may have any of the forms
accepted by Tk_GetColor. This option defaults to
black. If color is an empty string then no outline
will be drawn for the oval.
-stipple bitmap
Indicates that the oval should be filled in a stip-
ple pattern; bitmap specifies the stipple pattern
to use, in any of the forms accepted by Tk_Get-
Bitmap. If the -fill option hasn't been specified
then this option has no effect. If bitmap is an
empty string (the default), then filling is done in
a solid fashion.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width outlineWidth
outlineWidth specifies the width of the outline to
be drawn around the oval, in any of the forms
described in the COORDINATES section above. If the
-outline option hasn't been specified then this
option has no effect. Wide outlines are drawn cen-
tered on the oval path defined by x1, y1, x2, and
y2. This option defaults to 1.0.
POLYGON ITEMS
Items of type polygon appear as polygonal or curved filled
regions on the display. Polygons are created with widget
commands of the following form:
pathName create polygon x1 y1 ... xn yn ?option value option value ...?
The arguments x1 through yn specify the coordinates for
three or more points that define a closed polygon. The
first and last points may be the same; whether they are
or not, Tk will draw the polygon as a closed polygon.
After the coordinates there may be any number of
option-value pairs, each of which sets one of the configu-
ration options for the item. These same option-value
pairs may be used in itemconfigure widget commands to
change the item's configuration. The following options
are supported for polygons:
-fill color
Color specifies a color to use for filling the area
of the polygon; it may have any of the forms
acceptable to Tk_GetColor. If color is an empty
string then the polygon will be transparent. This
option defaults to black.
-outline color
Color specifies a color to use for drawing the
polygon's outline; it may have any of the forms
accepted by Tk_GetColor. If color is an empty
string then no outline will be drawn for the poly-
gon. This option defaults to empty (no outline).
-smooth boolean
Boolean must have one of the forms accepted by
Tk_GetBoolean It indicates whether or not the poly-
gon should be drawn with a curved perimeter. If
so, the outline of the polygon becomes a set of
parabolic splines, one spline for the first and
second line segments, one for the second and third,
and so on. Straight-line segments can be generated
in a smoothed polygon by duplicating the end-points
of the desired line segment.
-splinesteps number
Specifies the degree of smoothness desired for
curves: each spline will be approximated with num-
ber line segments. This option is ignored unless
the -smooth option is true.
-stipple bitmap
Indicates that the polygon should be filled in a
stipple pattern; bitmap specifies the stipple pat-
tern to use, in any of the forms accepted by
Tk_GetBitmap. If bitmap is an empty string (the
default), then filling is done in a solid fashion.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width outlineWidth
OutlineWidth specifies the width of the outline to
be drawn around the polygon, in any of the forms
described in the COORDINATES section above. If the
-outline option hasn't been specified then this
option has no effect. This option defaults to 1.0.
Polygon items are different from other items such as rect-
angles, ovals and arcs in that interior points are consid-
ered to be ``inside'' a polygon (e.g. for purposes of the
find closest and find overlapping widget commands) even if
it is not filled. For most other item types, an interior
point is considered to be inside the item only if the item
is filled or if it has neither a fill nor an outline. If
you would like an unfilled polygon whose interior points
are not considered to be inside the polygon, use a line
item instead.
RECTANGLE ITEMS
Items of type rectangle appear as rectangular regions on
the display. Each rectangle may have an outline, a fill,
or both. Rectangles are created with widget commands of
the following form:
pathName create rectangle x1 y1 x2 y2 ?option value option value ...?
The arguments x1, y1, x2, and y2 give the coordinates of
two diagonally opposite corners of the rectangle (the
rectangle will include its upper and left edges but not
its lower or right edges). After the coordinates there
may be any number of option-value pairs, each of which
sets one of the configuration options for the item. These
same option-value pairs may be used in itemconfigure wid-
get commands to change the item's configuration. The fol-
lowing options are supported for rectangles:
-fill color
Fill the area of the rectangle with color, which
may be specified in any of the forms accepted by
Tk_GetColor. If color is an empty string (the
default), then the rectangle will not be filled.
-outline color
Draw an outline around the edge of the rectangle in
color. Color may have any of the forms accepted by
Tk_GetColor. This option defaults to black. If
color is an empty string then no outline will be
drawn for the rectangle.
-stipple bitmap
Indicates that the rectangle should be filled in a
stipple pattern; bitmap specifies the stipple pat-
tern to use, in any of the forms accepted by
Tk_GetBitmap. If the -fill option hasn't been
specified then this option has no effect. If
bitmap is an empty string (the default), then fill-
ing is done in a solid fashion.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width outlineWidth
OutlineWidth specifies the width of the outline to
be drawn around the rectangle, in any of the forms
described in the COORDINATES section above. If the
-outline option hasn't been specified then this
option has no effect. Wide outlines are drawn cen-
tered on the rectangular path defined by x1, y1,
x2, and y2. This option defaults to 1.0.
TEXT ITEMS
A text item displays a string of characters on the screen
in one or more lines. Text items support indexing and
selection, along with the following text-related canvas
widget commands: dchars, focus, icursor, index, insert,
select. Text items are created with widget commands of
the following form:
pathName create text x y ?option value option value ...?
The arguments x and y specify the coordinates of a point
used to position the text on the display (see the options
below for more information on how text is displayed).
After the coordinates there may be any number of
option-value pairs, each of which sets one of the configu-
ration options for the item. These same option-value
pairs may be used in itemconfigure widget commands to
change the item's configuration. The following options
are supported for text items:
-anchor anchorPos
AnchorPos tells how to position the text relative
to the positioning point for the text; it may have
any of the forms accepted by Tk_GetAnchor. For
example, if anchorPos is center then the text is
centered on the point; if anchorPos is n then the
text will be drawn such that the top center point
of the rectangular region occupied by the text will
be at the positioning point. This option defaults
to center.
-fill color
Color specifies a color to use for filling the text
characters; it may have any of the forms accepted
by Tk_GetColor. If this option isn't specified
then it defaults to black.
-font fontName
Specifies the font to use for the text item. Font-
Name may be any string acceptable to Tk_Get-
FontStruct. If this option isn't specified, it
defaults to a system-dependent font.
-justify how
Specifies how to justify the text within its bound-
ing region. How must be one of the values left,
right, or center. This option will only matter if
the text is displayed as multiple lines. If the
option is omitted, it defaults to left.
-stipple bitmap
Indicates that the text should be drawn in a stip-
pled pattern rather than solid; bitmap specifies
the stipple pattern to use, in any of the forms
accepted by Tk_GetBitmap. If bitmap is an empty
string (the default) then the text is drawn in a
solid fashion.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-text string
String specifies the characters to be displayed in
the text item. Newline characters cause line
breaks. The characters in the item may also be
changed with the insert and delete widget commands.
This option defaults to an empty string.
-width lineLength
Specifies a maximum line length for the text, in
any of the forms described in the COORDINATES sec-
tion above. If this option is zero (the default)
the text is broken into lines only at newline char-
acters. However, if this option is non-zero then
any line that would be longer than lineLength is
broken just before a space character to make the
line shorter than lineLength; the space character
is treated as if it were a newline character.
WINDOW ITEMS
Items of type window cause a particular window to be
displayed at a given position on the canvas. Window items
are created with widget commands of the following form:
pathName create window x y ?option value option value ...?
The arguments x and y specify the coordinates of a point
used to position the window on the display (see the
-anchor option below for more information on how bitmaps
are displayed). After the coordinates there may be any
number of option-value pairs, each of which sets one of
the configuration options for the item. These same
option-value pairs may be used in itemconfigure widget
commands to change the item's configuration. The follow-
ing options are supported for window items:
-anchor anchorPos
AnchorPos tells how to position the window relative
to the positioning point for the item; it may have
any of the forms accepted by Tk_GetAnchor. For
example, if anchorPos is center then the window is
centered on the point; if anchorPos is n then the
window will be drawn so that its top center point
is at the positioning point. This option defaults
to center.
-height pixels
Specifies the height to assign to the item's win-
dow. Pixels may have any of the forms described in
the COORDINATES section above. If this option
isn't specified, or if it is specified as an empty
string, then the window is given whatever height it
requests internally.
-tags tagList
Specifies a set of tags to apply to the item.
TagList consists of a list of tag names, which
replace any existing tags for the item. TagList
may be an empty list.
-width pixels
Specifies the width to assign to the item's window.
Pixels may have any of the forms described in the
COORDINATES section above. If this option isn't
specified, or if it is specified as an empty
string, then the window is given whatever width it
requests internally.
-window pathName
Specifies the window to associate with this item.
The window specified by pathName must either be a
child of the canvas widget or a child of some
ancestor of the canvas widget. PathName may not
refer to a top-level window.
Note: due to restrictions in the ways that windows are
managed, it is not possible to draw other graphical items
(such as lines and images) on top of window items. A win-
dow item always obscures any graphics that overlap it,
regardless of their order in the display list.
APPLICATION-DEFINED ITEM TYPES
It is possible for individual applications to define new
item types for canvas widgets using C code. See the docu-
mentation for Tk_CreateItemType.
BINDINGS
In the current implementation, new canvases are not given
any default behavior: you'll have to execute explicit Tcl
commands to give the canvas its behavior.
CREDITS
Tk's canvas widget is a blatant ripoff of ideas from Joel
Bartlett's ezd program. Ezd provides structured graphics
in a Scheme environment and preceded canvases by a year or
two. Its simple mechanisms for placing and animating
graphical objects inspired the functions of canvases.
KEYWORDS
canvas, widget