Provided by: tk8.6-doc_8.6.14-1build1_all 
NAME
canvas - Create and manipulate 'canvas' hypergraphics drawing surface widgets
SYNOPSIS
canvas pathName ?options?
STANDARD OPTIONS
-background -borderwidth -cursor
-highlightbackground -highlightcolor -highlightthickness
-insertbackground -insertborderwidth -insertofftime
-insertontime -insertwidth -relief
-selectbackground -selectborderwidth -selectforeground
-takefocus -xscrollcommand -yscrollcommand
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:-state
Database Name: state
Database Class: State
Modifies the default state of the canvas where state may be set to one of: normal, disabled, or
hidden. Individual canvas objects all have their own state option which may override the default
state. Many options can take separate specifications such that the appearance of the item can be
different in different situations. The options that start with active control the appearance when
the mouse pointer is over it, while the option starting with disabled controls the appearance when
the state is disabled. Canvas items which are disabled will not react to canvas bindings.
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
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 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
distances. 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.
________________________________________________________________________________________________________________
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 window 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 manipulated (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 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 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 Tk raise command and lower command 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” is not. 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 (different item types interpret this in varying
ways; see the individual item type documentation for details). 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.
tagOrId may contain a logical expressions of tags by using operators: “&&”, “||”, “^”, “!”, and
parenthesized subexpressions. For example:
.c find withtag {(a&&!b)||(!a&&b)}
or equivalently:
.c find withtag {a^b}
will find only those items with either “a” or “b” tags, but not both.
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 (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 floating-point numbers. Coordinates and distances are
specified in screen units, which are floating-point numbers optionally followed by one of several
letters. If no letter 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. Coordinates can be specified either as an even number
of parameters, or as a single list parameter containing an even number of x and y coordinate values.
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 origin
of the window using the xview and yview widget commands; this is typically used for scrolling. Canvases
do not support scaling or rotation 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.
Note that the default origin of the canvas's visible area is coincident with the origin for the whole
window as that makes bindings using the mouse position easier to work with; you only need to use the
canvasx and canvasy widget commands if you adjust the origin of the visible area. However, this also
means that any focus ring (as controlled by the -highlightthickness option) and window border (as
controlled by the -borderwidth option) must be taken into account before you get to the visible area of
the canvas.
INDICES
Text items support the notion of an index for identifying particular positions within the item. In a
similar fashion, line and polygon items support index for identifying, inserting and deleting subsets of
their coordinates. Indices are used for commands such as inserting or deleting a range of characters or
coordinates, 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. Lines and Polygons do not support the insertion cursor and the selection.
Their indices are supposed to be even always, because coordinates always appear in pairs.
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. If indexes are odd for lines and
polygons, they will be automatically decremented by one. 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. For polygons, numbers less than 0 or greater than the
length of the coordinate list will be adjusted by adding or subtracting the length until the
result is between zero and the length, inclusive.
end Refers to the character or coordinate just after the last one in the item (same as the number
of characters or coordinates in the item).
insert Refers to the character just before which the insertion cursor is drawn in this item. Not valid
for lines and polygons.
sel.first Refers to the first selected character in the item. If the selection is not in this item then
this form is illegal.
sel.last Refers to the last selected character in the item. If the selection is not in this item then
this form is illegal.
@x,y Refers to the character or coordinate 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.
DASH PATTERNS
Many items support the notion of a dash pattern for outlines.
The first possible syntax is a list of integers. Each element represents the number of pixels of a line
segment. Only the odd segments are drawn using the “outline” color. The other segments are drawn
transparent.
The second possible syntax is a character list containing only 5 possible characters “.,-_ ”. The space
can be used to enlarge the space between other line elements, and cannot occur as the first position in
the string. Some examples:
-dash . → -dash {2 4}
-dash - → -dash {6 4}
-dash -. → -dash {6 4 2 4}
-dash -.. → -dash {6 4 2 4 2 4}
-dash {. } → -dash {2 8}
-dash , → -dash {4 4}
The main difference of this syntax with the previous is that it is shape-conserving. This means that all
values in the dash list will be multiplied by the line width before display. This assures that “.” will
always be displayed as a dot and “-” always as a dash regardless of the line width.
On systems which support only a limited set of dash patterns, the dash pattern will be displayed as the
closest dash pattern that is available. For example, on Windows only the first 4 of the above examples
are available. The last 2 examples will be displayed identically to the first one.
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 is not 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 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 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 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 than 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 than 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 binding).
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, ButtonPress, Motion, and KeyPress) or virtual events. 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. 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 trigger 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 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 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 pathName (see Tk_ConfigureInfo for information 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 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 ...?
pathName coords tagOrId ?coordList?
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 coordinates for the named item. If
tagOrId refers to multiple items, then the first one in the display list is used.
Note that for rectangles, ovals and arcs the returned list of coordinates has a fixed order,
namely the left, top, right and bottom coordinates, which may not be the order originally given.
Also the coordinates are always returned in screen units with no units (that is, in pixels). So if
the original coordinates were specified for instance in centimeters or inches, the returned values
will nevertheless be in pixels.
pathName create type x y ?x y ...? ?option value ...?
pathName create type coordList ?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 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, or coordinates, in the range given by first
and last, inclusive. If some of the items given by tagOrId do not support indexing operations
then they ignore this operation. Text items interpret first and last as indices to a character,
line and polygon items interpret them as indices to a coordinate (an x,y pair). Indices are
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 does not 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
command. 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
several items, then the focus is set to the first such item in the display list that supports the
insertion cursor. If tagOrId does not refer to any items, or if none of them support the
insertion cursor, then the focus is not 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 does not
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 was not 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 display
list. If tagOrId does not 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
character whose position is given by index. If some or all of the items given by tagOrId do not
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 focus widget command, above), but the
cursor position may be set even when the item does not have the focus. This command returns an
empty string.
pathName imove tagOrId index x y
This command causes the index'th coordinate of each of the items indicated by tagOrId to be 2
relocated to the location (x,y). Each item interprets index independently according to the rules 2
described in INDICES above. Out of the standard set of items, only line and polygon items may have 2
their coordinates relocated this way.
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.
Text items interpret index as an index to a character, line and polygon items interpret it as an
index to a coordinate (an x,y pair). The return value is guaranteed to lie between 0 and the
number of characters, or coordinates, 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 display list order).
pathName insert tagOrId beforeThis string
For each of the items given by tagOrId, if the item supports text or coordinate, insertion then
string is inserted into the item's text just before the character, or coordinate, whose index is
beforeThis. Text items interpret beforeThis as an index to a character, line and polygon items
interpret it as an index to a coordinate (an x,y pair). For lines and polygons the string must be
a valid coordinate sequence. 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 describing all of the available options for the first
item given by tagOrId (see Tk_ConfigureInfo for information 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 display 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
command and lower command, not the raise widget command and lower widget command for canvases.
This command 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 associated with the item and yAmount to the y-coordinate of each point
associated with the item. This command returns an empty string.
pathName moveto tagOrId xPos yPos
Move the items given by tagOrId in the canvas coordinate space so that the first coordinate pair 2
(the upper-left corner of the bounding box) of the first item (the lowest in the display list) 2
with tag tagOrId is located at position (xPos,yPos). xPos and yPos may be the empty string, in 2
which case the corresponding coordinate will be unchanged. All items matching tagOrId remain in 2
the same positions relative to each other. 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
specified then the Postscript is written to a file and an empty string is returned; otherwise the
Postscript is returned as the result of the command. 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 created in Encapsulated Postscript form
using version 3.0 of the Document Structuring Conventions. Note: by default Postscript is only
generated for information 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 following options are supported:
-channel channelName
Specifies the name of the channel to which to write the Postscript. If this option and the
-file option are not specified then the Postscript is returned as the result of the
command.
-colormap varName
VarName must be the name of an array variable 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 has not been specified, or if there is no 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 and the
-channel option are not specified then the Postscript is returned as the result of the
command.
-fontmap varName
VarName must be the name of an array variable that specifies a font mapping to use in the
Postscript. Each element of varName must consist of a Tcl list with two elements, 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 element 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 canvas 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 positioning
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 factor from -pagewidth is used (non-uniform scaling is not
implemented).
-pagex position
Position gives the x-coordinate of the positioning 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 positioning 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 output 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 canvas 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 display list is used as the destination
location for the moved items. This command returns an empty string.
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 command and lower command, not
the raise widget command and lower widget command for canvases.
pathName rchars tagOrId first last string
This command causes the text or coordinates between first and last for each of the items indicated 2
by tagOrId to be replaced by string. Each item interprets first and last independently according 2
to the rules described in INDICES above. Out of the standard set of items, text items support this 2
operation by altering their text as directed, and line and polygon items support this operation by 2
altering their coordinate list (in which case string should be a list of coordinates to use as a 2
replacement). The other items ignore this operation.
pathName scale tagOrId xOrigin yOrigin xScale yScale
Rescale the coordinates of 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.
Note that some items have only a single pair of coordinates (e.g., text, images and windows) and
so scaling of them by this command can only move them around.
pathName scan option args
This command is used to implement scanning on canvases. 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 ?gain?
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 widget.
It then adjusts the view by gain times the difference in coordinates, where gain defaults
to 10. 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 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 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 is not 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 is not 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 does not 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 widget. If the selection anchor point for the widget is not
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
does not 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 element is .6, 20% of the canvas's area (as defined
by the -scrollregion option) is off-screen to the left, the middle 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 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 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 element 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 yScrollIncrement 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 do not support indexing or selection or the commands related
to them, such as index and insert. Where items do support these facilities, it is noted explicitly in
the descriptions below. At present, text, line and polygon items provide this support. For lines and
polygons the indexing facility is used to manipulate the coordinates of the item.
COMMON ITEM OPTIONS
Many items share a common set of options. These options are explained here, and then referred to be each
widget type for brevity.
-anchor anchorPos
AnchorPos tells how to position the item 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 item
is centered on the point; if anchorPos is n then the item will be drawn so that its top center
point is at the positioning point. This option defaults to center.
-dash pattern
-activedash pattern
-disableddash pattern
This option specifies dash patterns for the normal, active state, and disabled state of an item.
pattern may have any of the forms accepted by Tk_GetDash. If the dash options are omitted then
the default is a solid outline. See DASH PATTERNS for more information.
-dashoffset offset
The starting offset in pixels into the pattern provided by the -dash option. -dashoffset is
ignored if there is no -dash pattern. The offset may have any of the forms described in the
COORDINATES section above.
-fill color
-activefill color
-disabledfill color
Specifies the color to be used to fill item's area. in its normal, active, and disabled states.
The even-odd fill rule is used. Color may have any of the forms accepted by Tk_GetColor. For the
line item, it specifies the color of the line drawn. For the text item, it specifies the
foreground color of the text. If color is an empty string (the default for all canvas items
except line and text), then the item will not be filled.
-outline color
-activeoutline color
-disabledoutline color
This option specifies the color that should be used to draw the outline of the item in its normal,
active and disabled states. Color may have any of the forms accepted by Tk_GetColor. If color is
specified as an empty string then no outline is drawn for the item.
-offset offset
Specifies the offset of stipples. The offset value can be of the form x,y or side, where side can
be n, ne, e, se, s, sw, w, nw, or center. In the first case the origin is the origin of the
toplevel of the current window. For the canvas itself and canvas objects the origin is the canvas
origin, but putting # in front of the coordinate pair indicates using the toplevel origin instead.
For canvas objects, the -offset option is used for stippling as well. For the line and polygon
canvas items you can also specify an index as argument, which connects the stipple origin to one
of the coordinate points of the line/polygon. Note that stipple offsets are only supported on X11;
they are silently ignored on other platforms.
-outlinestipple bitmap
-activeoutlinestipple bitmap
-disabledoutlinestipple bitmap
This option specifies stipple patterns that should be used to draw the outline of the item in its
normal, active and disabled states. Indicates that the outline for the item 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 has not 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. Note that
stipples are not well supported on platforms that do not use X11 as their drawing API.
-outlineoffset offset
Specifies the offset of the stipple pattern used for outlines, in the same way that the -outline
option controls fill stipples. (See the -outline option for a description of the syntax of
offset.)
-stipple bitmap
-activestipple bitmap
-disabledstipple bitmap
This option specifies stipple patterns that should be used to fill the item in its normal, active
and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by
Tk_GetBitmap. If the -fill option has not been specified then this option has no effect. If
bitmap is an empty string (the default), then filling is done in a solid fashion. For the text
item, it affects the actual text. Note that stipples are not well supported on platforms that do
not use X11 as their drawing API.
-state state
This allows an item to override the canvas widget's global state option. It takes the same values:
normal, disabled or hidden.
-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
-activewidth outlineWidth
-disabledwidth outlineWidth
Specifies the width of the outline to be drawn around the item's region, in its normal, active and
disabled states. outlineWidth may be 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. This option defaults to 1.0. For arcs, wide outlines will be drawn centered on the edges
of the arc's region.
STANDARD ITEM TYPES
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 ...?
pathName create arc coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList 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 configuration.
An arc item becomes the current item when the mouse pointer is over any part that is painted or (when
fully transparent) that would be painted if both the -fill and -outline options were non-empty.
The following standard options are supported by arcs:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra 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.
-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 positive or
negative.
-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. 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.
BITMAP ITEMS
Items of type bitmap appear on the display as images with two colors, foreground and background. Bitmaps
are created with widget commands of the following form:
pathName create bitmap x y ?option value ...?
pathName create bitmap coordList ?option value ...?
The arguments x and y or coordList (which must have two elements) specify the coordinates of a point used
to position the bitmap on the display, as controlled by the -anchor option. 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. A bitmap item becomes the current item when the mouse pointer is over any part of its
bounding box.
The following standard options are supported by bitmaps:
-anchor -state
-tags
The following extra options are supported for bitmaps:
-background color
-activebackground color
-disabledbackground color
Specifies the color to use for each of the bitmap's “0” valued pixels in its normal, active and
disabled states. Color may have any of the forms accepted by Tk_GetColor. If this option is not
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
-activebitmap bitmap
-disabledbitmap bitmap
Specifies the bitmaps to display in the item in its normal, active and disabled states. Bitmap
may have any of the forms accepted by Tk_GetBitmap.
-foreground color
-activeforeground color
-disabledforeground color
Specifies the color to use for each of the bitmap's “1” valued pixels in its normal, active and
disabled states. Color may have any of the forms accepted by Tk_GetColor.
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 ...?
pathName create image coordList ?option value ...?
The arguments x and y or coordList specify the coordinates of a point used to position the image on the
display, as controlled by the -anchor option. 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. An
image item becomes the current item when the mouse pointer is over any part of its bounding box.
The following standard options are supported by images:
-anchor -state
-tags
The following extra options are supported for images:
-image name
-activeimage name
-disabledimage name
Specifies the name of the images to display in the item in is normal, active and disabled states.
This image must have been created previously with the image create command.
LINE ITEMS
Items of type line appear on the display as one or more connected line segments or curves. Line items
support coordinate indexing operations using the dchars, index and insert widget commands. Lines are
created with widget commands of the following form:
pathName create line x1 y1... xn yn ?option value ...?
pathName create line coordList ?option value ...?
The arguments x1 through yn or coordList 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. A
line item is the current item whenever the mouse pointer is over any segment of the line, whether drawn
or not and whether or not the line is smoothed.
The following standard options are supported by lines:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra 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. When requested to draw an arrowhead, Tk internally adjusts
the corresponding line end point so that the rendered line ends at the neck of the arrowhead
rather than at its tip so that the line doesn't extend past the edge of the arrowhead. This may
trigger a Leave event if the mouse is hovering this line end. Conversely, when removing an
arrowhead Tk adjusts the corresponding line point the other way round, which may trigger an Enter
event.
-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 is not 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, projecting, or round). If this option is not
specified then it defaults to butt. Where arrowheads are drawn the cap style is ignored.
-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_GetJoinStyle (bevel, miter, or round). If this option is not
specified then it defaults to round. If the line only contains two points then this option is
irrelevant.
-smooth smoothMethod
smoothMethod must have one of the forms accepted by Tcl_GetBoolean or a line smoothing method.
Only true and raw are supported in the core (with bezier being an alias for true), but more can be
added at runtime. If a boolean false value or empty string is given, no smoothing is applied. A
boolean truth value assumes true smoothing. If the smoothing method is true, this indicates that
the line should be drawn as a curve, rendered as a set of quadratic 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. If the smoothing method is raw, this indicates that the line should also be drawn as a
curve but where the list of coordinates is such that the first coordinate pair (and every third
coordinate pair thereafter) is a knot point on a cubic Bezier curve, and the other coordinates are
control points on the cubic Bezier curve. Straight line segments can be generated within a curve
by making control points equal to their neighbouring knot points. If the last point is a control
point and not a knot point, the point is repeated (one or two times) so that it also becomes a
knot point.
-splinesteps number
Specifies the degree of smoothness desired for curves: each spline will be approximated with
number line segments. This option is ignored unless the -smooth option is true or raw.
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 ...?
pathName create oval coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList 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 circular; 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 configuration. An oval item becomes the current item
when the mouse pointer is over any part that is painted or (when fully transparent) that would be painted
if both the -fill and -outline options were non-empty.
The following standard options are supported by ovals:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
There are no oval-specific options.
POLYGON ITEMS
Items of type polygon appear as polygonal or curved filled regions on the display. Polygon items support
coordinate indexing operations using the dchars, index and insert widget commands. Polygons are created
with widget commands of the following form:
pathName create polygon x1 y1 ... xn yn ?option value ...?
pathName create polygon coordList ?option value ...?
The arguments x1 through yn or coordList specify the coordinates for three or more points that define a
polygon. The first point should not be repeated as the last to close the shape; Tk will automatically
close the periphery between the first and last points. 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. A
polygon item is the current item whenever the mouse pointer is over any part of the polygon, whether
drawn or not and whether or not the outline is smoothed.
The following standard options are supported by polygons:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra options are supported for polygons:
-joinstyle style
Specifies the ways in which joints are to be drawn at the vertices of the outline. Style may have
any of the forms accepted by Tk_GetJoinStyle (bevel, miter, or round). If this option is not
specified then it defaults to round.
-smooth boolean
Boolean must have one of the forms accepted by Tcl_GetBoolean or a line smoothing method. Only
true and raw are supported in the core (with bezier being an alias for true), but more can be
added at runtime. If a boolean false value or empty string is given, no smoothing is applied. A
boolean truth value assumes true smoothing. If the smoothing method is true, this indicates that
the polygon should be drawn as a curve, rendered as a set of quadratic 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. If the smoothing method is raw, this indicates that the polygon should also be drawn as
a curve but where the list of coordinates is such that the first coordinate pair (and every third
coordinate pair thereafter) is a knot point on a cubic Bezier curve, and the other coordinates are
control points on the cubic Bezier curve. Straight line segments can be generated within a curve
by making control points equal to their neighbouring knot points. If the last point is not the
second point of a pair of control points, the point is repeated (one or two times) so that it also
becomes the second point of a pair of control points (the associated knot point will be the first
control point).
-splinesteps number
Specifies the degree of smoothness desired for curves: each spline will be approximated with
number line segments. This option is ignored unless the -smooth option is true or raw.
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 ...?
pathName create rectangle coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList (which must have four elements) 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 widget commands to change the item's configuration. A rectangle item becomes the current
item when the mouse pointer is over any part that is painted or (when fully transparent) that would be
painted if both the -fill and -outline options were non-empty.
The following standard options are supported by rectangles:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
There are no rectangle-specific options.
TEXT ITEMS
A text item displays a string of characters on the screen in one or more lines. Text items support
indexing, editing and selection through the dchars widget command, the focus widget command, the icursor
widget command, the index widget command, the insert widget command, and the select widget command. Text
items are created with widget commands of the following form:
pathName create text x y ?option value ...?
pathName create text coordList ?option value ...?
The arguments x and y or coordList (which must have two elements) 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 configuration options for the item. These same option-value pairs may be used in itemconfigure
widget commands to change the item's configuration. A text item becomes the current item when the mouse
pointer is over any part of its bounding box.
The following standard options are supported by text items:
-anchor -fill
-activefill -disabledfill
-stipple -activestipple
-disabledstipple -state
-tags
The following extra options are supported for text items:
-angle rotationDegrees
RotationDegrees tells how many degrees to rotate the text anticlockwise about the positioning 2
point for the text; it may have any floating-point value from 0.0 to 360.0. For example, if 2
rotationDegrees is 90, then the text will be drawn vertically from bottom to top. This option 2
defaults to 0.0.
-font fontName
Specifies the font to use for the text item. FontName may be any string acceptable to Tk_GetFont.
If this option is not 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.
-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.
-underline
Specifies the integer index of a character within the text to be underlined. 0 corresponds to the
first character of the text displayed, 1 to the next character, and so on. -1 means that no
underline should be drawn (if the whole text item is to be underlined, the appropriate font should
be used instead).
-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 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 ...?
pathName create window coordList ?option value ...?
The arguments x and y or coordList (which must have two elements) specify the coordinates of a point used
to position the window on the display, as controlled by the -anchor option. 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. Theoretically, a window item becomes the current item when the mouse pointer is over any
part of its bounding box, but in practice this typically does not happen because the mouse pointer ceases
to be over the canvas at that point.
The following standard options are supported by window items:
-anchor -state
-tags
The following extra options are supported for window items:
-height pixels
Specifies the height to assign to the item's window. Pixels may have any of the forms described
in the COORDINATES section above. If this option is not specified, or if it is specified as zero,
then the window is given whatever height it requests internally.
-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 is not specified, or if it is specified as zero,
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 window item always obscures any
graphics that overlap it, regardless of their order in the display list. Also note that window items,
unlike other canvas items, are not clipped for display by their containing canvas's border, and are
instead clipped by the parent widget of the window specified by the -window option; when the parent
widget is the canvas, this means that the window item can overlap the canvas's border.
APPLICATION-DEFINED ITEM TYPES
It is possible for individual applications to define new item types for canvas widgets using C code. See
the documentation for Tk_CreateItemType.
BINDINGS
In the current implementation, new canvases are not given any default behavior: you will 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.
SEE ALSO
bind(3tk), font(3tk), image(3tk), scrollbar(3tk)
KEYWORDS
canvas, widget
Tk 8.3 canvas(3tk)