canvas
Section: Tk Built-In Commands (n)
Updated: 8.3
Page Index
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 relocated to the location (x,y).
Each item interprets index independently according to the rules
described in INDICES above. Out of the standard set of items, only line
and polygon items may have 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 of the bottommost item with
tag tagOrId is located at
position (xPos,yPos). xPos and yPos may be
the empty string, in which case the corresponding coordinate
will be unchanged. All items matching
tagOrId remain in 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 by tagOrId to be replaced by
string. Each item interprets first and last independently
according to the rules described in INDICES above. Out of the standard
set of items, text items support this operation by altering their text as
directed, and line and polygon items support this operation by altering their
coordinate list (in which case string should be a list of coordinates to
use as a 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,
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.
- -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 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 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 point for the text; it may have any floating-point value
from 0.0 to 360.0. For example, if rotationDegrees is 90, then the
text will be drawn vertically from bottom to top.
This option 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(n),
font(n),
image(n),
scrollbar(n)
KEYWORDS
canvas, widget