CANVAS(9)CANVAS(9)NAMEcanvas - Create and manipulate canvas widgets
SYNOPSIScanvas pathName ?options?
STANDARD OPTIONS-background-selectbackground-takefocus
-borderwidth-selectborderwidth -xscrollcommand
-relief-selectforeground-yscrollcommand
WIDGET-SPECIFIC OPTIONS
-closeenough dist
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.
-confine boolean
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 option. Defaults to true, which
means that the view will be constrained within the scroll
region.
-height dist
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.
-scrollregion list
Specifies a list with four dist 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.
-width dist
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.
-xscrollincrement dist
Specifies an increment for horizontal scrolling, in any of the
usual forms permitted for screen distances. 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 multiple of
xscrollicrement; 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 xscrollicrement. If the value of
this option is less than or equal to zero, then horizontal
scrolling is unconstrained.
-yscrollincrement dist
Specifies an increment for vertical scrolling, in any of the
usual forms permitted for screen distances. If the value of
this option is greater than zero, the vertical view in the win‐
dow will be constrained so that the canvas y coordinate at the
top edge of the window is always an even multiple of yscrolli‐
crement; 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 yscrollicrement. If the value of this
option is less than or equal to zero, then vertical scrolling is
unconstrained.
-buffer what
Specifies how much of the canvas region will be backed by an
offscreen bitmap buffer. What can be one of all (the entire
scroll region will be buffered), visible (only the visible
area), none (no buffering) or auto (equivalent to either none or
visible depending on whether the canvas is packed inside another
canvas or not).
INTRODUCTION
The canvas command creates a new window (given by the pathName argu‐
ment) and makes it into a canvas widget. Additional options, described
above, may be specified on the command line to configure aspects of the
canvas such as its colours and 3-D relief. The canvas command returns
its pathName argument. At the time this command is invoked, there must
not exist a window named pathName.
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 manipulated (e.g. moved or re-coloured) and
commands may be associated with items in much the same way that the
bind command allows commands to be bound to widgets. For example, a
particular command may be associated with the <Button-1> event so that
the command is invoked whenever button 1 is pressed with the mouse cur‐
sor over an item. This means that items in a canvas can have behav‐
iours defined by the Tk 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 every‐
thing else. Widget commands may be used to re-arrange the order of the
display list.
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 cur‐
rent item, which is the topmost item whose drawn area covers the posi‐
tion 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 behaviour is for the command to use the first (lowest) of
these items in the display list that is suitable for the command.
Exceptions are noted in the widget command descriptions below.
COORDINATES
All coordinates related to canvases are stored as fixed-point numbers.
Coordinates and distances are specified as documented in the dist sec‐
tion of types(9).
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 coordinate system relative to the ori‐
gin 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 window coordinate
system.
Individual items may be moved or scaled using widget commands 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 inser‐
tion 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. 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 cur‐
sor 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 coordinate 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 character in the
line that is closest to the given point.
WIDGET COMMAND
The canvas command creates a new Tk 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 behaviour 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 overlap 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 consid‐
ered 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 topmost 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 argu‐
ment had not been specified.
enclosed x1 y1 x2 y2
Selects all the items completely enclosed within the rec‐
tangular 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 approximate 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 matching 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 substitutions 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 existing binding rather than replacing it).
In this case the return value is an empty string. If command is
omitted then the command returns the command associated with
tagOrId and sequence (an error occurs if there is no such bind‐
ing). If both command and sequence are omitted then the command
returns a list of all the sequences for which bindings 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, Button‐
Press, Motion, and KeyPress. The handling of events in canvases
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. Key‐
board-related events are directed to the focus item, if any (see
the focus widget command below for more on this).
It is possible for multiple bindings to match a particular
event. This could occur, for example, if one binding is associ‐
ated 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 multiple 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 ter‐
minates 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 bind‐
ings 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 loca‐
tion. 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 loca‐
tion. 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 can‐
vas command.
pathName configure ?option? ?value? ?option value ...?
Query or modify the configuration options of the widget. If no
option is specified, returns a list of all of the available
options for pathName. 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 command returns a list whose
elements are the coordinates of the item named by tagOrId. If
coordinates are specified, then they replace the current coordi‐
nates 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 con‐
sist of the coordinates for one or more points, followed by
specifications for zero or more item options. See the subsec‐
tions on individual item types below for more on the syntax 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 characters in the
range given by first and last, inclusive. 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 unaf‐
fected 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 command. If searchCommand is enclosed, overlapping, or
all, the items are returned in display-list order, i.e. bottom‐
most first.
pathName focus ?tagOrId?
Set the keyboard focus for the canvas widget to the item given
by tagOrId. If tagOrId refers to several items, then the focus
is set to the first such item in the display list that supports
the insertion 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 cur‐
rently 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 indepen‐
dent: a given item doesn't actually have the input focus unless
(a) its canvas is the focus window 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 associated 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 dis‐
play list. If tagOrId doesn't refer to any items, then an error
is returned. If the item contains no tags, then an empty string
is returned.
pathName grab what tagOrId
Does for canvas widgets what grab(9) does for normal tk widgets:
mouse events will only be delivered to tagOrId. If tagOrId
refers to more than one item, then the first such item in the
display list is grabbed. What is as described in grab(9).
Note that the canvas grab item, as set by this command, and the tk grab
item, as set by grab(9) are totally independent; a canvas item doesn't
actually grab the mouse unless a) the canvas itself has grabbed the
mouse or b) the mouse events are being delivered to the canvas as a
matter of course.
pathName icursor tagOrId index
Set the position of the insertion cursor for the item(s) given
by tagOrId to just before the character 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 wid‐
get 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, inclusive. If tagOrId
refers to multiple items, then the index is processed in the
first of these items that supports indexing operations (in dis‐
play 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 wid‐
get. 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 display list is
used as the destination location for the moved items. This com‐
mand returns an empty string.
pathName move tagOrId xAmount yAmount
Move each of the items given by tagOrId in the canvas coordinate
space by adding xAmount to the x-coordinate of each point asso‐
ciated with the item and yAmount to the y-coordinate of each
point associated with the item. This command returns an empty
string.
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 display list is used as the des‐
tination location for the moved items. 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 screenx canvasx
Given an x-coordinate canvasx in the canvas, this command
returns the equivalent screen x-coordinate.
pathName screeny canvasy
Given an x-coordinate canvasy in the canvas, this command
returns the equivalent screen y-coordinate.
pathName see x1 y1 ?x2 y2?
Adjusts the view in the window such that, if possible the point
[x1, y1] (and, if given, the point [x2, y2]) are made visible.
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 descriptions below, tagOrId must refer to an item
that supports indexing and selection; if it refers to multiple
items then the first of these that supports indexing and the
selection is used. Index gives a textual description of a posi‐
tion 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 widget 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 characters 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 wid‐
get. If the selection anchor point for the widget isn't
currently in tagOrId, then it is set to the same charac‐
ter 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 horizontal 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 horizontal span that is visible in the window. For
example, if the first element is .2 and the second ele‐
ment 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 scrollbars via the -xscrollcommand option.
pathName xview moveto fraction
Adjusts the view in the window so that fraction 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. If what is units,
the view adjusts left or right in units of the xscrolli‐
crement option, if it is greater than zero, or in units
of one-tenth the window'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 vertical 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 ele‐
ment is 1.0, the lowest 40% of the canvas's area (as
defined by the -scrollregion option) is visible in the
window. These are the same values passed to scrollbars
via the -yscrollcommand option.
pathName yview moveto fraction
Adjusts the view in the window so that fraction 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 yscrollicre‐
ment option, if it is greater than zero, or in units of
one-tenth the window'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 characterized 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 commands related
to them, such as index and insert. Where items do support these facil‐
ities, 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 (spec‐
ified 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 itemconfig‐
ure widget commands to change the item's configuration. 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 negative. If it is greater than 360 or less than -360, then
degrees modulo 360 is used as the extent.
-fill colour
Fill the region of the arc with colour. If colour is an empty
string (the default), then the arc will not be filled.
-outline colour
Colour specifies a colour to use for drawing the arc's outline.
This option defaults to black. If colour is specified as an
empty string then no outline is drawn for the arc.
-start degrees
Specifies the beginning of the angular range occupied by the
arc. Degrees is given in units of degrees measured counter-
clockwise from the 3-o'clock position; it may be either posi‐
tive or negative.
-stipple bitmap
Indicates that the arc should be filled in a stipple pattern;
bitmap specifies the stipple pattern to use. 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. The results are undefined if bitmap is not a
1-bit image.
-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 segments, 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 section. This type is not imple‐
mented at the moment. It behaves as arc. If type is arc then
the arc's region consists 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 outlines 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 colours,
foreground and background. Bitmaps are created 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 posi‐
tion 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 configu‐
ration. The following options are supported for bitmaps:
-anchor anchorPos
AnchorPos tells how to position the bitmap relative to the posi‐
tioning point for the item. 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.
-bitmap bitmap
Specifies the bitmap to display in the item.
-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 canvas. Images are
created with widget commands of the following form:
pathName create image x y ?option value option value ...?
The arguments x and y specify the coordinates of a point used to posi‐
tion 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 posi‐
tioning point for the item. 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 fol‐
lowing 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 following 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 argu‐
ment must be a list with three elements, each specifying a dis‐
tance 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 ``rea‐
sonable'' shape.
-capstyle style
Specifies the ways in which caps are to be drawn at the end‐
points of the line. Style may one of butt, projecting, or
round. If this option isn't specified then it defaults to butt.
Where arrowheads are drawn the cap style is ignored. Note that
the first two options currently have the same effect.
-fill colour
Colour specifies a colour to use for drawing the line. It may
also be an empty string, in which case the line will be trans‐
parent. This option defaults to black.
-smooth boolean
Boolean indicates whether or not the line should be drawn as a
curve. If so, the line is rendered as a set of Bezier splines:
one spline is drawn for the first and second line segments, 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.
-stipple bitmap
Indicates that the line should be filled in a stipple pattern;
bitmap specifies the stipple pattern to use. If bitmap is an
empty string (the default), then filling is done in a solid
fashion. The results are undefined if bitmap is not a 1-bit
image.
-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 following 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 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 configu‐
ration. The following options are supported for ovals:
-fill colour
Fill the area of the oval with colour. If colour is an empty
string (the default), then then the oval will not be filled.
-outline colour
Colour specifies a colour to use for drawing the oval's outline.
This option defaults to black. If colour is an empty string
then no outline will be drawn for the oval.
-stipple bitmap
Indicates that the oval should be filled in a stipple pattern;
bitmap specifies the stipple pattern to use. 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. The results are undefined if bitmap is not a
1-bit image.
-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 COORDI‐
NATES section above. If the -outline option hasn't been speci‐
fied then this option has no effect. Wide outlines are drawn
centered 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 follow‐
ing 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 configuration options
for the item. These same option-value pairs may be used in itemconfig‐
ure widget commands to change the item's configuration. The following
options are supported for polygons:
-fill colour
Colour specifies a colour to use for filling the area of the
polygon. If colour is an empty string then the polygon will be
transparent. This option defaults to the empty string (trans‐
parent).
-outline colour
Colour specifies a colour to use for drawing the polygon's out‐
line. If colour is an empty string then no outline will be
drawn for the polygon. This option defaults to black.
-smooth boolean
Boolean indicates whether or not the polygon should be drawn
with a curved perimeter. If so, the outline of the polygon
becomes a set of Bezier 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.
-stipple bitmap
Indicates that the polygon should be filled in a stipple pat‐
tern; bitmap specifies the stipple pattern to use. If bitmap is
an empty string (the default), then filling is done in a solid
fashion. The results are undefined if bitmap is not a 1-bit
image.
-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.
-winding type
Specifies the winding rule to use when filling the polygon.
Type can be either nonzero (the default) or odd See fillpoly in
draw-image(2) for an explanation.
-width outlineWidth
OutlineWidth specifies the width of the outline to be drawn
around the polygon, in any of the forms described in the COORDI‐
NATES section above. If the -outline option hasn't been speci‐
fied then this option has no effect. This option defaults to
1.0.
Polygon items are different from other items such as rectangles, ovals
and arcs in that interior points are considered 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 coordi‐
nates 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 rectangles:
-fill colour
Fill the area of the rectangle with colour. If colour is an
empty string (the default), then the rectangle will not be
filled.
-outline colour
Draw an outline around the edge of the rectangle in colour.
This option defaults to black. If colour 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 pat‐
tern; bitmap specifies the stipple pattern to use. 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. The results are undefined if bitmap is not a
1-bit image.
-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 COOR‐
DINATES section above. If the -outline option hasn't been spec‐
ified then this option has no effect. Wide outlines are drawn
centered 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 posi‐
tion the text on the display (see the options below for more informa‐
tion on how text is displayed). After the coordinates there may be any
number of option-value pairs, each of which sets one of the configura‐
tion 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 posi‐
tioning point for the text. 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 position‐
ing point. This option defaults to center.
-fill colour
Colour specifies a colour to use for filling the text charac‐
ters. If this option isn't specified then it defaults to black.
-font font
Specifies the font to use for the text item. If this option
isn't specified, it defaults to a system-dependent font.
-justify how
Specifies how to justify the text within its bounding 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 stippled pattern
rather than solid; bitmap specifies the stipple pattern to use.
If bitmap is an empty string (the default) then the text is
drawn in a solid fashion. The results are undefined if bitmap
is not a 1-bit image.
-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 section above. If this
option is zero (the default) the text is broken into lines only
at newline characters. 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 line‐
Length; 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 posi‐
tion 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 configu‐
ration. The following options are supported for window items:
-anchor anchorPos
AnchorPos tells how to position the window relative to the posi‐
tioning point for the item. 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 dist
Specifies the height to assign to the item's window. Dist 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 dist
Specifies the width to assign to the item's window. Dist 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 wid‐
get or a child of some ancestor of the canvas widget. PathName
may not refer to a top-level window.
BINDINGS
New canvases are not given any default behaviour. Use bind(2) commands
to give the canvas its behaviour.
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 can‐
vases.
SEE ALSOoptions(9), types(9)CANVAS(9)
