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canvas(n) Tk Built-In Commands canvas(n)
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NAME
canvas - Create and manipulate canvas 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 can-vas's canvas's
vas'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 man-ager. manager.
ager. 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 man-ager. manager.
ager. 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 yScrollIncre-ment. yScrollIncrement.
ment. 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-col-ored) re-colored)
ored) 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 <But-
ton-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 raise and lower Tk commands instead.
ITEM IDS AND TAGS
Items in a canvas widget may be named in either of two ways: by id or by tag. Each item has a unique
identifying number, which is assigned to that item when it is created. The id of an item never
changes and id numbers are never re-used within the lifetime of a canvas widget.
Each item may also have any number of tags associated with it. A tag is just a string of characters,
and it may take any form except that of an integer. For example, "x123" is OK but "123" is not. The
same tag may be associated with many different items. This is commonly done to group items in vari-ous various
ous 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 opera-tions operations
tions 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 com-mand command
mand 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 dis-tance distance
tance 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 con-taining containing
taining 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 charac-ters characters
ters 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 then the length of the coordinate list will be adjusted by adding or subtract-ing subtracting
ing 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 num-ber number
ber 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 possi-ble possible
ble 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 dis-play display
play 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 dis-play display
play 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 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 can-vas canvas
vas 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 exist-ing existing
ing 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 key-board keyboard
board (such as Enter, Leave, ButtonPress, Motion, and KeyPress) or virtual events. The han-dling handling
dling 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 cur-rent current
rent 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 exam-ple, example,
ple, 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 associ-ated associated
ated 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 match-ing matching
ing 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-coordi-nate x-coordinate
nate that is displayed at that location. If gridspacing is specified, then the canvas coordi-nate coordinate
nate 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 informa-tion information
tion on the format of this list). If option is specified with no value, then the command
returns a list describing the one named option (this list will be identical to the correspond-ing corresponding
ing 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 val-ues values
ues accepted by the canvas command.
pathName coords tagOrId ?x_ y_ ...?
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.
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 dchars. Text items interpret first and last as indices to a char-acter, character,
acter, line and polygon items interpret them 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 com-mand command
mand 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 sup-ports supports
ports the insertion cursor. If tagOrId does not refer to any items, or if none of them sup-port support
port 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 widget command focus,
below), but the cursor position may be set even when the item does not 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. Text items interpret index as an index to a character, line and polygon items inter-pret interpret
pret 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 and lower commands, not the raise and lower widget commands
for canvases. This command returns an empty string.
pathName move tagOrId xAmount yAmount
Move each of the items given by tagOrId in the 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 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 Encapsu-lated Encapsulated
lated 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:
-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 par-ticular particular
ticular color value (e.g. "1.0 1.0 0.0 setrgbcolor"). When outputting color informa-tion information
tion 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 com-mand command
mand 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 is not
specified then the Postscript is returned as the result of the command instead of being
written to a file.
-fontmap varName
VarName must be the name of an array 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 con-tained contained
tained 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 posi-tioning positioning
tioning point on the page (which is given by the -pagex and -pagey options). For exam-ple, example,
ple, -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 ("por-trait"orientation); ("portrait"orientation);
trait"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. Note: this command has no effect on
window items. Window items always obscure other item types, and the stacking order of window
items is determined by the raise and lower commands, not the raise and lower widget commands
for canvases. This command returns an empty string.
pathName scale tagOrId xOrigin yOrigin xScale yScale
Rescale all of the items given by tagOrId in canvas coordinate space. XOrigin and yOrigin
identify the origin for the scaling operation and xScale and yScale identify the scale factors
for x- and y-coordinates, respectively (a scale factor of 1.0 implies no change to that coor-dinate). coordinate).
dinate). For each of the points defining each item, the x-coordinate is adjusted to change
the distance from xOrigin by a factor of xScale. Similarly, each y-coordinate is adjusted to
change the distance from yOrigin by a factor of yScale. This command returns an empty string.
pathName scan option args
This command is used to implement scanning on 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 wid-get. widget.
get. 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 win-dow's window's
dow's width otherwise. If what is pages then the view adjusts in units of nine-tenths
the window's width. If number is negative then information farther to the left becomes
visible; if it is positive then information farther to the right becomes visible.
pathName yview ?args?
This command is used to query and change the 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 exam-ple, example,
ple, 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.
-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, Color may have any of the forms accepted by Tk_GetColor. If color is an empty string
(the default), then the item will not be filled. For the line item, it specifies the color of
the line drawn. For the text item, it specifies the foreground color of the text.
-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.
This option defaults to black. 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.
-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. The offset value can be of the
form "x,y" or the description of a side (one of n, ne, e, se, s, sw, w, nw, or center). This
option only has an effect when the outline is drawn as a stipple pattern, and is only sup-ported supported
ported under X11.
-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.
ARC ITEMS
Items of type arc appear on the display as arc-shaped regions. An arc is a section of an oval delim-ited delimited
ited by two angles (specified by the -start and -extent options) and displayed in one of several ways
(specified by the -style option). Arcs are created with widget commands of the following form:
pathName create arc x1 y1 x2 y2 ?option value option value ...?
pathName create arc coordList ?option value 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 con-figuration. configuration.
figuration. 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 option value ...?
pathName create bitmap coordList ?option value 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 (see the -anchor option below for more information on how
bitmaps are displayed). After the coordinates there may be any number of option-value pairs, each of
which sets one of the configuration options for the item. These same option-value pairs may be used
in itemconfigure widget commands to change the item's configuration. A bitmap item becomes the cur-rent current
rent item when the mouse pointer is over any part of its bounding box.
The following standard options are supported by bitmaps:
-state
-tags
The following extra options are supported for bitmaps:
-anchor anchorPos
AnchorPos tells how to position the bitmap relative to the positioning point for the item; it
may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then
the bitmap is centered on the point; if anchorPos is n then the bitmap will be drawn so that
its top center point is at the positioning point. This option defaults to center.
-background color
-activebackground bitmap
-disabledbackground bitmap
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. Bit-map Bitmap
map may have any of the forms accepted by Tk_GetBitmap.
-foreground color
-activeforeground bitmap
-disabledforeground bitmap
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 and defaults to
black.
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 ...?
pathName create image coordList ?option value option value ...?
The arguments x and y or coordList specify the coordinates of a point used to position the image on
the display (see the -anchor option below for more information). After the coordinates there may be
any number of option-value pairs, each of which sets one of the configuration options for the item.
These same option-value pairs may be used in itemconfigure widget commands to change the item's con-figuration. configuration.
figuration. 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:
-state
-tags
The following extra options are supported for images:
-anchor anchorPos
AnchorPos tells how to position the image relative to the positioning point for the item; it
may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then
the image is centered on the point; if anchorPos is n then the image will be drawn so that
its top center point is at the positioning point. This option defaults to center.
-image name
-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 canvas widget commands: dchars, index, insert.
Lines are created with widget commands of the following form:
pathName create line x1 y1... xn yn ?option value option value ...?
pathName create line coordList ?option value 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 arrow-heads arrowheads
heads at both ends). This option defaults to none.
-arrowshape shape
This option indicates how to draw arrowheads. The shape argument must be a list with three
elements, each specifying a distance in any of the forms described in the COORDINATES section
above. The first element of the list gives the distance along the line from the neck of the
arrowhead to its tip. The second element gives the distance along the line from the trailing
points of the arrowhead to the tip, and the third element gives the distance from the outside
edge of the line to the trailing points. If this option 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_GetCapStyle (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 coor- |
dinate 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 option value ...?
pathName create oval coordList ?option value 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 rec-tangle rectangle
tangle 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
POLYGON ITEMS
Items of type polygon appear as polygonal or curved filled regions on the display. Polygon items
support coordinate indexing operations using the canvas widget commands: dchars, index, insert.
Polygons are created with widget commands of the following form:
pathName create polygon x1 y1 ... xn yn ?option value option value ...?
pathName create polygon coordList ?option value 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 automati-cally automatically
cally 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 con-figuration. configuration.
figuration. 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
-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_GetCapStyle (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 coor- |
dinate 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 venerated 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 over-lapping overlapping
lapping 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 out-line. outline.
line. 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 ...?
pathName create rectangle coordList ?option value 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
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 ...?
pathName create text coordList ?option value 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 itemcon-figure itemconfigure
figure 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:
-fill
-activefill
-disabledfill
-stipple
-activestipple
-disabledstipple
-state
-tags
The following extra options are supported for text items:
-anchor anchorPos
AnchorPos tells how to position the text relative to the positioning point for the text; it
may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then
the text is centered on the point; if anchorPos is n then the text will be drawn such that
the top center point of the rectangular region occupied by the text will be at the positioning
point. This option defaults to center.
-font fontName
Specifies the font to use for the text item. FontName may be any string acceptable to Tk_Get-Font. Tk_GetFont.
Font. 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. |
-under- |
line | |
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 line-Length; lineLength;
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 ...?
pathName create window coordList ?option value 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 (see the -anchor option below for more information on how
bitmaps are displayed). After the coordinates there may be any number of option-value pairs, each of
which sets one of the configuration options for the item. These same option-value pairs may be used
in itemconfigure widget commands to change the item's configuration. 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:
-state
-tags
The following extra options are supported for window items:
-anchor anchorPos
AnchorPos tells how to position the window relative to the positioning point for the item; it
may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then
the window is centered on the point; if anchorPos is n then the window will be drawn so that
its top center point is at the positioning point. This option defaults to center.
-height pixels
Specifies the height to assign to the item's 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 mech-anisms mechanisms
anisms for placing and animating graphical objects inspired the functions of canvases.
SEE ALSO
bind(n), font(n), image(n), scrollbar(n)
KEYWORDS
canvas, widget
Tk 8.3 canvas(n)
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