Provided by: tk8.6-doc_8.6.14-1build1_all 
NAME
canvas - Create and manipulate 'canvas' hypergraphics drawing surface widgets
SYNOPSIS
canvas pathName ?options?
STANDARD OPTIONS
-background -borderwidth -cursor
-highlightbackground -highlightcolor -highlightthickness
-insertbackground -insertborderwidth -insertofftime
-insertontime -insertwidth -relief
-selectbackground -selectborderwidth -selectforeground
-takefocus -xscrollcommand -yscrollcommand
See the options manual entry for details on the standard options.
WIDGET-SPECIFIC OPTIONS
Command-Line Name:-closeenough
Database Name: closeEnough
Database Class: CloseEnough
Specifies a floating-point value indicating how close the mouse cursor must be to
an item before it is considered to be “inside” the item. Defaults to 1.0.
Command-Line Name:-confine
Database Name: confine
Database Class: Confine
Specifies a boolean value that indicates whether or not it should be allowable to
set the canvas's view outside the region defined by the scrollRegion argument.
Defaults to true, which means that the view will be constrained within the scroll
region.
Command-Line Name:-height
Database Name: height
Database Class: Height
Specifies a desired window height that the canvas widget should request from its
geometry manager. The value may be specified in any of the forms described in the
COORDINATES section below.
Command-Line Name:-scrollregion
Database Name: scrollRegion
Database Class: ScrollRegion
Specifies a list with four coordinates describing the left, top, right, and bottom
coordinates of a rectangular region. This region is used for scrolling purposes
and is considered to be the boundary of the information in the canvas. Each of the
coordinates may be specified in any of the forms given in the COORDINATES section
below.
Command-Line Name:-state
Database Name: state
Database Class: State
Modifies the default state of the canvas where state may be set to one of: normal,
disabled, or hidden. Individual canvas objects all have their own state option
which may override the default state. Many options can take separate specifications
such that the appearance of the item can be different in different situations. The
options that start with active control the appearance when the mouse pointer is
over it, while the option starting with disabled controls the appearance when the
state is disabled. Canvas items which are disabled will not react to canvas
bindings.
Command-Line Name:-width
Database Name: width
Database Class: width
Specifies a desired window width that the canvas widget should request from its
geometry manager. The value may be specified in any of the forms described in the
COORDINATES section below.
Command-Line Name:-xscrollincrement
Database Name: xScrollIncrement
Database Class: ScrollIncrement
Specifies an increment for horizontal scrolling, in any of the usual forms
permitted for screen distances. If the value of this option is greater than zero,
the horizontal view in the window will be constrained so that the canvas x
coordinate at the left edge of the window is always an even multiple of
xScrollIncrement; furthermore, the units for scrolling (e.g., the change in view
when the left and right arrows of a scrollbar are selected) will also be
xScrollIncrement. If the value of this option is less than or equal to zero, then
horizontal scrolling is unconstrained.
Command-Line Name:-yscrollincrement
Database Name: yScrollIncrement
Database Class: ScrollIncrement
Specifies an increment for vertical scrolling, in any of the usual forms permitted
for screen distances. If the value of this option is greater than zero, the
vertical view in the window will be constrained so that the canvas y coordinate at
the top edge of the window is always an even multiple of yScrollIncrement;
furthermore, the units for scrolling (e.g., the change in view when the top and
bottom arrows of a scrollbar are selected) will also be yScrollIncrement. If the
value of this option is less than or equal to zero, then vertical scrolling is
unconstrained.
_________________________________________________________________________________________________
INTRODUCTION
The canvas command creates a new window (given by the pathName argument) and makes it into
a canvas widget. Additional options, described above, may be specified on the command
line or in the option database to configure aspects of the canvas such as its colors and
3-D relief. The canvas command returns its pathName argument. At the time this command is
invoked, there must not exist a window named pathName, but pathName's parent must exist.
Canvas widgets implement structured graphics. A canvas displays any number of items,
which may be things like rectangles, circles, lines, and text. Items may be manipulated
(e.g. moved or re-colored) and commands may be associated with items in much the same way
that the bind command allows commands to be bound to widgets. For example, a particular
command may be associated with the <Button-1> event so that the command is invoked
whenever button 1 is pressed with the mouse cursor over an item. This means that items in
a canvas can have behaviors defined by the Tcl scripts bound to them.
DISPLAY LIST
The items in a canvas are ordered for purposes of display, with the first item in the
display list being displayed first, followed by the next item in the list, and so on.
Items later in the display list obscure those that are earlier in the display list and are
sometimes referred to as being “on top” of earlier items. When a new item is created it
is placed at the end of the display list, on top of everything else. Widget commands may
be used to re-arrange the order of the display list.
Window items are an exception to the above rules. The underlying window systems require
them always to be drawn on top of other items. In addition, the stacking order of window
items is not affected by any of the canvas widget commands; you must use the Tk raise
command and lower command instead.
ITEM IDS AND TAGS
Items in a canvas widget may be named in either of two ways: by id or by tag. Each item
has a unique identifying number, which is assigned to that item when it is created. The id
of an item never changes and id numbers are never re-used within the lifetime of a canvas
widget.
Each item may also have any number of tags associated with it. A tag is just a string of
characters, and it may take any form except that of an integer. For example, “x123” is OK
but “123” is not. The same tag may be associated with many different items. This is
commonly done to group items in various interesting ways; for example, all selected items
might be given the tag “selected”.
The tag all is implicitly associated with every item in the canvas; it may be used to
invoke operations on all the items in the canvas.
The tag current is managed automatically by Tk; it applies to the current item, which is
the topmost item whose drawn area covers the position of the mouse cursor (different item
types interpret this in varying ways; see the individual item type documentation for
details). If the mouse is not in the canvas widget or is not over an item, then no item
has the current tag.
When specifying items in canvas widget commands, if the specifier is an integer then it is
assumed to refer to the single item with that id. If the specifier is not an integer,
then it is assumed to refer to all of the items in the canvas that have a tag matching the
specifier. The symbol tagOrId is used below to indicate that an argument specifies either
an id that selects a single item or a tag that selects zero or more items.
tagOrId may contain a logical expressions of tags by using operators: “&&”, “||”, “^”,
“!”, and parenthesized subexpressions. For example:
.c find withtag {(a&&!b)||(!a&&b)}
or equivalently:
.c find withtag {a^b}
will find only those items with either “a” or “b” tags, but not both.
Some widget commands only operate on a single item at a time; if tagOrId is specified in a
way that names multiple items, then the normal behavior is for the command to use the
first (lowest) of these items in the display list that is suitable for the command.
Exceptions are noted in the widget command descriptions below.
COORDINATES
All coordinates related to canvases are stored as floating-point numbers. Coordinates and
distances are specified in screen units, which are floating-point numbers optionally
followed by one of several letters. If no letter is supplied then the distance is in
pixels. If the letter is m then the distance is in millimeters on the screen; if it is c
then the distance is in centimeters; i means inches, and p means printers points (1/72
inch). Larger y-coordinates refer to points lower on the screen; larger x-coordinates
refer to points farther to the right. Coordinates can be specified either as an even
number of parameters, or as a single list parameter containing an even number of x and y
coordinate values.
TRANSFORMATIONS
Normally the origin of the canvas coordinate system is at the upper-left corner of the
window containing the canvas. It is possible to adjust the origin of the canvas
coordinate system relative to the origin of the window using the xview and yview widget
commands; this is typically used for scrolling. Canvases do not support scaling or
rotation of the canvas coordinate system relative to the window coordinate system.
Individual items may be moved or scaled using widget commands described below, but they
may not be rotated.
Note that the default origin of the canvas's visible area is coincident with the origin
for the whole window as that makes bindings using the mouse position easier to work with;
you only need to use the canvasx and canvasy widget commands if you adjust the origin of
the visible area. However, this also means that any focus ring (as controlled by the
-highlightthickness option) and window border (as controlled by the -borderwidth option)
must be taken into account before you get to the visible area of the canvas.
INDICES
Text items support the notion of an index for identifying particular positions within the
item. In a similar fashion, line and polygon items support index for identifying,
inserting and deleting subsets of their coordinates. Indices are used for commands such
as inserting or deleting a range of characters or coordinates, and setting the insertion
cursor position. An index may be specified in any of a number of ways, and different types
of items may support different forms for specifying indices. Text items support the
following forms for an index; if you define new types of text-like items, it would be
advisable to support as many of these forms as practical. Note that it is possible to
refer to the character just after the last one in the text item; this is necessary for
such tasks as inserting new text at the end of the item. Lines and Polygons do not
support the insertion cursor and the selection. Their indices are supposed to be even
always, because coordinates always appear in pairs.
number A decimal number giving the position of the desired character within the text
item. 0 refers to the first character, 1 to the next character, and so on. If
indexes are odd for lines and polygons, they will be automatically decremented
by one. A number less than 0 is treated as if it were zero, and a number
greater than the length of the text item is treated as if it were equal to the
length of the text item. For polygons, numbers less than 0 or greater than the
length of the coordinate list will be adjusted by adding or subtracting the
length until the result is between zero and the length, inclusive.
end Refers to the character or coordinate just after the last one in the item (same
as the number of characters or coordinates in the item).
insert Refers to the character just before which the insertion cursor is drawn in this
item. Not valid for lines and polygons.
sel.first Refers to the first selected character in the item. If the selection is not in
this item then this form is illegal.
sel.last Refers to the last selected character in the item. If the selection is not in
this item then this form is illegal.
@x,y Refers to the character or coordinate at the point given by x and y, where x and
y are specified in the coordinate system of the canvas. If x and y lie outside
the coordinates covered by the text item, then they refer to the first or last
character in the line that is closest to the given point.
DASH PATTERNS
Many items support the notion of a dash pattern for outlines.
The first possible syntax is a list of integers. Each element represents the number of
pixels of a line segment. Only the odd segments are drawn using the “outline” color. The
other segments are drawn transparent.
The second possible syntax is a character list containing only 5 possible characters “.,-_
”. The space can be used to enlarge the space between other line elements, and cannot
occur as the first position in the string. Some examples:
-dash . → -dash {2 4}
-dash - → -dash {6 4}
-dash -. → -dash {6 4 2 4}
-dash -.. → -dash {6 4 2 4 2 4}
-dash {. } → -dash {2 8}
-dash , → -dash {4 4}
The main difference of this syntax with the previous is that it is shape-conserving. This
means that all values in the dash list will be multiplied by the line width before
display. This assures that “.” will always be displayed as a dot and “-” always as a dash
regardless of the line width.
On systems which support only a limited set of dash patterns, the dash pattern will be
displayed as the closest dash pattern that is available. For example, on Windows only the
first 4 of the above examples are available. The last 2 examples will be displayed
identically to the first one.
WIDGET COMMAND
The canvas command creates a new Tcl command whose name is pathName. This command may be
used to invoke various operations on the widget. It has the following general form:
pathName option ?arg arg ...?
Option and the args determine the exact behavior of the command. The following widget
commands are possible for canvas widgets:
pathName addtag tag searchSpec ?arg arg ...?
For each item that meets the constraints specified by searchSpec and the args, add
tag to the list of tags associated with the item if it is not already present on
that list. It is possible that no items will satisfy the constraints given by
searchSpec and args, in which case the command has no effect. This command returns
an empty string as result. SearchSpec and arg's may take any of the following
forms:
above tagOrId
Selects the item just after (above) the one given by tagOrId in the display
list. If tagOrId denotes more than one item, then the last (topmost) of
these items in the display list is used.
all Selects all the items in the canvas.
below tagOrId
Selects the item just before (below) the one given by tagOrId in the display
list. If tagOrId denotes more than one item, then the first (lowest) of
these items in the display list is used.
closest x y ?halo? ?start?
Selects the item closest to the point given by x and y. If more than one
item is at the same closest distance (e.g. two items overlap the point),
then the top-most of these items (the last one in the display list) is used.
If halo is specified, then it must be a non-negative value. Any item closer
than halo to the point is considered to overlap it. The start argument may
be used to step circularly through all the closest items. If start is
specified, it names an item using a tag or id (if by tag, it selects the
first item in the display list with the given tag). Instead of selecting
the topmost closest item, this form will select the topmost closest item
that is below start in the display list; if no such item exists, then the
selection behaves as if the start argument had not been specified.
enclosed x1 y1 x2 y2
Selects all the items completely enclosed within the rectangular region
given by x1, y1, x2, and y2. X1 must be no greater than x2 and y1 must be
no greater than y2.
overlapping x1 y1 x2 y2
Selects all the items that overlap or are enclosed within the rectangular
region given by x1, y1, x2, and y2. X1 must be no greater than x2 and y1
must be no greater than y2.
withtag tagOrId
Selects all the items given by tagOrId.
pathName bbox tagOrId ?tagOrId tagOrId ...?
Returns a list with four elements giving an approximate bounding box for all the
items named by the tagOrId arguments. The list has the form “x1 y1 x2 y2” such
that the drawn areas of all the named elements are within the region bounded by x1
on the left, x2 on the right, y1 on the top, and y2 on the bottom. The return
value may overestimate the actual bounding box by a few pixels. If no items match
any of the tagOrId arguments or if the matching items have empty bounding boxes
(i.e. they have nothing to display) then an empty string is returned.
pathName bind tagOrId ?sequence? ?command?
This command associates command with all the items given by tagOrId such that
whenever the event sequence given by sequence occurs for one of the items the
command will be invoked. This widget command is similar to the bind command except
that it operates on items in a canvas rather than entire widgets. See the bind
manual entry for complete details on the syntax of sequence and the substitutions
performed on command before invoking it. If all arguments are specified then a new
binding is created, replacing any existing binding for the same sequence and
tagOrId (if the first character of command is “+” then command augments an existing
binding rather than replacing it). In this case the return value is an empty
string. If command is omitted then the command returns the command associated with
tagOrId and sequence (an error occurs if there is no such binding). If both
command and sequence are omitted then the command returns a list of all the
sequences for which bindings have been defined for tagOrId.
The only events for which bindings may be specified are those related to the mouse
and keyboard (such as Enter, Leave, ButtonPress, Motion, and KeyPress) or virtual
events. The handling of events in canvases uses the current item defined in ITEM
IDS AND TAGS above. Enter and Leave events trigger for an item when it becomes the
current item or ceases to be the current item; note that these events are different
than Enter and Leave events for windows. Mouse-related events are directed to the
current item, if any. Keyboard-related events are directed to the focus item, if
any (see the focus widget command below for more on this). If a virtual event is
used in a binding, that binding can trigger only if the virtual event is defined by
an underlying mouse-related or keyboard-related event.
It is possible for multiple bindings to match a particular event. This could
occur, for example, if one binding is associated with the item's id and another is
associated with one of the item's tags. When this occurs, all of the matching
bindings are invoked. A binding associated with the all tag is invoked first,
followed by one binding for each of the item's tags (in order), followed by a
binding associated with the item's id. If there are multiple matching bindings for
a single tag, then only the most specific binding is invoked. A continue command
in a binding script terminates that script, and a break command terminates that
script and skips any remaining scripts for the event, just as for the bind command.
If bindings have been created for a canvas window using the bind command, then they
are invoked in addition to bindings created for the canvas's items using the bind
widget command. The bindings for items will be invoked before any of the bindings
for the window as a whole.
pathName canvasx screenx ?gridspacing?
Given a window x-coordinate in the canvas screenx, this command returns the canvas
x-coordinate that is displayed at that location. If gridspacing is specified, then
the canvas coordinate is rounded to the nearest multiple of gridspacing units.
pathName canvasy screeny ?gridspacing?
Given a window y-coordinate in the canvas screeny this command returns the canvas
y-coordinate that is displayed at that location. If gridspacing is specified, then
the canvas coordinate is rounded to the nearest multiple of gridspacing units.
pathName cget option
Returns the current value of the configuration option given by option. Option may
have any of the values accepted by the canvas command.
pathName configure ?option? ?value? ?option value ...?
Query or modify the configuration options of the widget. If no option is
specified, returns a list describing all of the available options for pathName (see
Tk_ConfigureInfo for information on the format of this list). If option is
specified with no value, then the command returns a list describing the one named
option (this list will be identical to the corresponding sublist of the value
returned if no option is specified). If one or more option-value pairs are
specified, then the command modifies the given widget option(s) to have the given
value(s); in this case the command returns an empty string. Option may have any of
the values accepted by the canvas command.
pathName coords tagOrId ?x0 y0 ...?
pathName coords tagOrId ?coordList?
Query or modify the coordinates that define an item. If no coordinates are
specified, this command returns a list whose elements are the coordinates of the
item named by tagOrId. If coordinates are specified, then they replace the current
coordinates for the named item. If tagOrId refers to multiple items, then the
first one in the display list is used.
Note that for rectangles, ovals and arcs the returned list of coordinates has a
fixed order, namely the left, top, right and bottom coordinates, which may not be
the order originally given. Also the coordinates are always returned in screen
units with no units (that is, in pixels). So if the original coordinates were
specified for instance in centimeters or inches, the returned values will
nevertheless be in pixels.
pathName create type x y ?x y ...? ?option value ...?
pathName create type coordList ?option value ...?
Create a new item in pathName of type type. The exact format of the arguments
after type depends on type, but usually they consist of the coordinates for one or
more points, followed by specifications for zero or more item options. See the
subsections on individual item types below for more on the syntax of this command.
This command returns the id for the new item.
pathName dchars tagOrId first ?last?
For each item given by tagOrId, delete the characters, or coordinates, in the range
given by first and last, inclusive. If some of the items given by tagOrId do not
support indexing operations then they ignore this operation. Text items interpret
first and last as indices to a character, line and polygon items interpret them as
indices to a coordinate (an x,y pair). Indices are described in INDICES above. If
last is omitted, it defaults to first. This command returns an empty string.
pathName delete ?tagOrId tagOrId ...?
Delete each of the items given by each tagOrId, and return an empty string.
pathName dtag tagOrId ?tagToDelete?
For each of the items given by tagOrId, delete the tag given by tagToDelete from
the list of those associated with the item. If an item does not have the tag
tagToDelete then the item is unaffected by the command. If tagToDelete is omitted
then it defaults to tagOrId. This command returns an empty string.
pathName find searchCommand ?arg arg ...?
This command returns a list consisting of all the items that meet the constraints
specified by searchCommand and arg's. SearchCommand and args have any of the forms
accepted by the addtag command. The items are returned in stacking order, with the
lowest item first.
pathName focus ?tagOrId?
Set the keyboard focus for the canvas widget to the item given by tagOrId. If
tagOrId refers to several items, then the focus is set to the first such item in
the display list that supports the insertion cursor. If tagOrId does not refer to
any items, or if none of them support the insertion cursor, then the focus is not
changed. If tagOrId is an empty string, then the focus item is reset so that no
item has the focus. If tagOrId is not specified then the command returns the id
for the item that currently has the focus, or an empty string if no item has the
focus.
Once the focus has been set to an item, the item will display the insertion cursor
and all keyboard events will be directed to that item. The focus item within a
canvas and the focus window on the screen (set with the focus command) are totally
independent: a given item does not actually have the input focus unless (a) its
canvas is the focus window and (b) the item is the focus item within the canvas.
In most cases it is advisable to follow the focus widget command with the focus
command to set the focus window to the canvas (if it was not there already).
pathName gettags tagOrId
Return a list whose elements are the tags associated with the item given by
tagOrId. If tagOrId refers to more than one item, then the tags are returned from
the first such item in the display list. If tagOrId does not refer to any items,
or if the item contains no tags, then an empty string is returned.
pathName icursor tagOrId index
Set the position of the insertion cursor for the item(s) given by tagOrId to just
before the character whose position is given by index. If some or all of the items
given by tagOrId do not support an insertion cursor then this command has no effect
on them. See INDICES above for a description of the legal forms for index. Note:
the insertion cursor is only displayed in an item if that item currently has the
keyboard focus (see the focus widget command, above), but the cursor position may
be set even when the item does not have the focus. This command returns an empty
string.
pathName imove tagOrId index x y
This command causes the index'th coordinate of each of the items indicated by │
tagOrId to be 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 (the upper-left corner of the bounding box) of the first item (the │
lowest in the display list) 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. The even-odd fill rule is used. Color may have any of the forms
accepted by Tk_GetColor. For the line item, it specifies the color of the line
drawn. For the text item, it specifies the foreground color of the text. If color
is an empty string (the default for all canvas items except line and text), then
the item will not be filled.
-outline color
-activeoutline color
-disabledoutline color
This option specifies the color that should be used to draw the outline of the item
in its normal, active and disabled states. Color may have any of the forms
accepted by Tk_GetColor. If color is specified as an empty string then no outline
is drawn for the item.
-offset offset
Specifies the offset of stipples. The offset value can be of the form x,y or side,
where side can be n, ne, e, se, s, sw, w, nw, or center. In the first case the
origin is the origin of the toplevel of the current window. For the canvas itself
and canvas objects the origin is the canvas origin, but putting # in front of the
coordinate pair indicates using the toplevel origin instead. For canvas objects,
the -offset option is used for stippling as well. For the line and polygon canvas
items you can also specify an index as argument, which connects the stipple origin
to one of the coordinate points of the line/polygon. Note that stipple offsets are
only supported on X11; they are silently ignored on other platforms.
-outlinestipple bitmap
-activeoutlinestipple bitmap
-disabledoutlinestipple bitmap
This option specifies stipple patterns that should be used to draw the outline of
the item in its normal, active and disabled states. Indicates that the outline for
the item should be drawn with a stipple pattern; bitmap specifies the stipple
pattern to use, in any of the forms accepted by Tk_GetBitmap. If the -outline
option has not been specified then this option has no effect. If bitmap is an
empty string (the default), then the outline is drawn in a solid fashion. Note
that stipples are not well supported on platforms that do not use X11 as their
drawing API.
-outlineoffset offset
Specifies the offset of the stipple pattern used for outlines, in the same way that
the -outline option controls fill stipples. (See the -outline option for a
description of the syntax of offset.)
-stipple bitmap
-activestipple bitmap
-disabledstipple bitmap
This option specifies stipple patterns that should be used to fill the item in its
normal, active and disabled states. bitmap specifies the stipple pattern to use,
in any of the forms accepted by Tk_GetBitmap. If the -fill option has not been
specified then this option has no effect. If bitmap is an empty string (the
default), then filling is done in a solid fashion. For the text item, it affects
the actual text. Note that stipples are not well supported on platforms that do
not use X11 as their drawing API.
-state state
This allows an item to override the canvas widget's global state option. It takes
the same values: normal, disabled or hidden.
-tags tagList
Specifies a set of tags to apply to the item. TagList consists of a list of tag
names, which replace any existing tags for the item. TagList may be an empty list.
-width outlineWidth
-activewidth outlineWidth
-disabledwidth outlineWidth
Specifies the width of the outline to be drawn around the item's region, in its
normal, active and disabled states. outlineWidth may be in any of the forms
described in the COORDINATES section above. If the -outline option has been
specified as an empty string then this option has no effect. This option defaults
to 1.0. For arcs, wide outlines will be drawn centered on the edges of the arc's
region.
STANDARD ITEM TYPES
ARC ITEMS
Items of type arc appear on the display as arc-shaped regions. An arc is a section of an
oval delimited by two angles (specified by the -start and -extent options) and displayed
in one of several ways (specified by the -style option). Arcs are created with widget
commands of the following form:
pathName create arc x1 y1 x2 y2 ?option value ...?
pathName create arc coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList give the coordinates of two diagonally
opposite corners of a rectangular region enclosing the oval that defines the arc. After
the coordinates there may be any number of option-value pairs, each of which sets one of
the configuration options for the item. These same option-value pairs may be used in
itemconfigure widget commands to change the item's configuration. An arc item becomes the
current item when the mouse pointer is over any part that is painted or (when fully
transparent) that would be painted if both the -fill and -outline options were non-empty.
The following standard options are supported by arcs:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra options are supported for arcs:
-extent degrees
Specifies the size of the angular range occupied by the arc. The arc's range
extends for degrees degrees counter-clockwise from the starting angle given by the
-start option. Degrees may be negative. If it is greater than 360 or less than
-360, then degrees modulo 360 is used as the extent.
-start degrees
Specifies the beginning of the angular range occupied by the arc. Degrees is given
in units of degrees measured counter-clockwise from the 3-o'clock position; it may
be either positive or negative.
-style type
Specifies how to draw the arc. If type is pieslice (the default) then the arc's
region is defined by a section of the oval's perimeter plus two line segments, one
between the center of the oval and each end of the perimeter section. If type is
chord then the arc's region is defined by a section of the oval's perimeter plus a
single line segment connecting the two end points of the perimeter section. If
type is arc then the arc's region consists of a section of the perimeter alone. In
this last case the -fill option is ignored.
BITMAP ITEMS
Items of type bitmap appear on the display as images with two colors, foreground and
background. Bitmaps are created with widget commands of the following form:
pathName create bitmap x y ?option value ...?
pathName create bitmap coordList ?option value ...?
The arguments x and y or coordList (which must have two elements) specify the coordinates
of a point used to position the bitmap on the display, as controlled by the -anchor
option. After the coordinates there may be any number of option-value pairs, each of
which sets one of the configuration options for the item. These same option-value pairs
may be used in itemconfigure widget commands to change the item's configuration. A bitmap
item becomes the current item when the mouse pointer is over any part of its bounding box.
The following standard options are supported by bitmaps:
-anchor -state
-tags
The following extra options are supported for bitmaps:
-background color
-activebackground color
-disabledbackground color
Specifies the color to use for each of the bitmap's “0” valued pixels in its
normal, active and disabled states. Color may have any of the forms accepted by
Tk_GetColor. If this option is not specified, or if it is specified as an empty
string, then nothing is displayed where the bitmap pixels are 0; this produces a
transparent effect.
-bitmap bitmap
-activebitmap bitmap
-disabledbitmap bitmap
Specifies the bitmaps to display in the item in its normal, active and disabled
states. Bitmap may have any of the forms accepted by Tk_GetBitmap.
-foreground color
-activeforeground color
-disabledforeground color
Specifies the color to use for each of the bitmap's “1” valued pixels in its
normal, active and disabled states. Color may have any of the forms accepted by
Tk_GetColor.
IMAGE ITEMS
Items of type image are used to display images on a canvas. Images are created with
widget commands of the following form:
pathName create image x y ?option value ...?
pathName create image coordList ?option value ...?
The arguments x and y or coordList specify the coordinates of a point used to position the
image on the display, as controlled by the -anchor option. After the coordinates there
may be any number of option-value pairs, each of which sets one of the configuration
options for the item. These same option-value pairs may be used in itemconfigure widget
commands to change the item's configuration. An image item becomes the current item when
the mouse pointer is over any part of its bounding box.
The following standard options are supported by images:
-anchor -state
-tags
The following extra options are supported for images:
-image name
-activeimage name
-disabledimage name
Specifies the name of the images to display in the item in is normal, active and
disabled states. This image must have been created previously with the image
create command.
LINE ITEMS
Items of type line appear on the display as one or more connected line segments or curves.
Line items support coordinate indexing operations using the dchars, index and insert
widget commands. Lines are created with widget commands of the following form:
pathName create line x1 y1... xn yn ?option value ...?
pathName create line coordList ?option value ...?
The arguments x1 through yn or coordList give the coordinates for a series of two or more
points that describe a series of connected line segments. After the coordinates there may
be any number of option-value pairs, each of which sets one of the configuration options
for the item. These same option-value pairs may be used in itemconfigure widget commands
to change the item's configuration. A line item is the current item whenever the mouse
pointer is over any segment of the line, whether drawn or not and whether or not the line
is smoothed.
The following standard options are supported by lines:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra options are supported for lines:
-arrow where
Indicates whether or not arrowheads are to be drawn at one or both ends of the
line. Where must have one of the values none (for no arrowheads), first (for an
arrowhead at the first point of the line), last (for an arrowhead at the last point
of the line), or both (for arrowheads at both ends). This option defaults to none.
When requested to draw an arrowhead, Tk internally adjusts the corresponding line
end point so that the rendered line ends at the neck of the arrowhead rather than
at its tip so that the line doesn't extend past the edge of the arrowhead. This may
trigger a Leave event if the mouse is hovering this line end. Conversely, when
removing an arrowhead Tk adjusts the corresponding line point the other way round,
which may trigger an Enter event.
-arrowshape shape
This option indicates how to draw arrowheads. The shape argument must be a list
with three elements, each specifying a distance in any of the forms described in
the COORDINATES section above. The first element of the list gives the distance
along the line from the neck of the arrowhead to its tip. The second element gives
the distance along the line from the trailing points of the arrowhead to the tip,
and the third element gives the distance from the outside edge of the line to the
trailing points. If this option is not specified then Tk picks a “reasonable”
shape.
-capstyle style
Specifies the ways in which caps are to be drawn at the endpoints of the line.
Style may have any of the forms accepted by Tk_GetCapStyle (butt, projecting, or
round). If this option is not specified then it defaults to butt. Where
arrowheads are drawn the cap style is ignored.
-joinstyle style
Specifies the ways in which joints are to be drawn at the vertices of the line.
Style may have any of the forms accepted by Tk_GetJoinStyle (bevel, miter, or
round). If this option is not specified then it defaults to round. If the line
only contains two points then this option is irrelevant.
-smooth smoothMethod
smoothMethod must have one of the forms accepted by Tcl_GetBoolean or a line
smoothing method. Only true and raw are supported in the core (with bezier being
an alias for true), but more can be added at runtime. If a boolean false value or
empty string is given, no smoothing is applied. A boolean truth value assumes true
smoothing. If the smoothing method is true, this indicates that the line should be
drawn as a curve, rendered as a set of quadratic splines: one spline is drawn for
the first and second line segments, one for the second and third, and so on.
Straight-line segments can be generated within a curve by duplicating the end-
points of the desired line segment. If the smoothing method is raw, this indicates
that the line should also be drawn as a curve but where the list of coordinates is
such that the first coordinate pair (and every third coordinate pair thereafter) is
a knot point on a cubic Bezier curve, and the other coordinates are control points
on the cubic Bezier curve. Straight line segments can be generated within a curve
by making control points equal to their neighbouring knot points. If the last point
is a control point and not a knot point, the point is repeated (one or two times)
so that it also becomes a knot point.
-splinesteps number
Specifies the degree of smoothness desired for curves: each spline will be
approximated with number line segments. This option is ignored unless the -smooth
option is true or raw.
OVAL ITEMS
Items of type oval appear as circular or oval regions on the display. Each oval may have
an outline, a fill, or both. Ovals are created with widget commands of the following form:
pathName create oval x1 y1 x2 y2 ?option value ...?
pathName create oval coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList give the coordinates of two diagonally
opposite corners of a rectangular region enclosing the oval. The oval will include the
top and left edges of the rectangle not the lower or right edges. If the region is square
then the resulting oval is circular; otherwise it is elongated in shape. After the
coordinates there may be any number of option-value pairs, each of which sets one of the
configuration options for the item. These same option-value pairs may be used in
itemconfigure widget commands to change the item's configuration. An oval item becomes the
current item when the mouse pointer is over any part that is painted or (when fully
transparent) that would be painted if both the -fill and -outline options were non-empty.
The following standard options are supported by ovals:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
There are no oval-specific options.
POLYGON ITEMS
Items of type polygon appear as polygonal or curved filled regions on the display.
Polygon items support coordinate indexing operations using the dchars, index and insert
widget commands. Polygons are created with widget commands of the following form:
pathName create polygon x1 y1 ... xn yn ?option value ...?
pathName create polygon coordList ?option value ...?
The arguments x1 through yn or coordList specify the coordinates for three or more points
that define a polygon. The first point should not be repeated as the last to close the
shape; Tk will automatically close the periphery between the first and last points. After
the coordinates there may be any number of option-value pairs, each of which sets one of
the configuration options for the item. These same option-value pairs may be used in
itemconfigure widget commands to change the item's configuration. A polygon item is the
current item whenever the mouse pointer is over any part of the polygon, whether drawn or
not and whether or not the outline is smoothed.
The following standard options are supported by polygons:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
The following extra options are supported for polygons:
-joinstyle style
Specifies the ways in which joints are to be drawn at the vertices of the outline.
Style may have any of the forms accepted by Tk_GetJoinStyle (bevel, miter, or
round). If this option is not specified then it defaults to round.
-smooth boolean
Boolean must have one of the forms accepted by Tcl_GetBoolean or a line smoothing
method. Only true and raw are supported in the core (with bezier being an alias for
true), but more can be added at runtime. If a boolean false value or empty string
is given, no smoothing is applied. A boolean truth value assumes true smoothing.
If the smoothing method is true, this indicates that the polygon should be drawn as
a curve, rendered as a set of quadratic splines: one spline is drawn for the first
and second line segments, one for the second and third, and so on. Straight-line
segments can be generated within a curve by duplicating the end-points of the
desired line segment. If the smoothing method is raw, this indicates that the
polygon should also be drawn as a curve but where the list of coordinates is such
that the first coordinate pair (and every third coordinate pair thereafter) is a
knot point on a cubic Bezier curve, and the other coordinates are control points on
the cubic Bezier curve. Straight line segments can be generated within a curve by
making control points equal to their neighbouring knot points. If the last point is
not the second point of a pair of control points, the point is repeated (one or two
times) so that it also becomes the second point of a pair of control points (the
associated knot point will be the first control point).
-splinesteps number
Specifies the degree of smoothness desired for curves: each spline will be
approximated with number line segments. This option is ignored unless the -smooth
option is true or raw.
Polygon items are different from other items such as rectangles, ovals and arcs in that
interior points are considered to be “inside” a polygon (e.g. for purposes of the find
closest and find overlapping widget commands) even if it is not filled. For most other
item types, an interior point is considered to be inside the item only if the item is
filled or if it has neither a fill nor an outline. If you would like an unfilled polygon
whose interior points are not considered to be inside the polygon, use a line item
instead.
RECTANGLE ITEMS
Items of type rectangle appear as rectangular regions on the display. Each rectangle may
have an outline, a fill, or both. Rectangles are created with widget commands of the
following form:
pathName create rectangle x1 y1 x2 y2 ?option value ...?
pathName create rectangle coordList ?option value ...?
The arguments x1, y1, x2, and y2 or coordList (which must have four elements) give the
coordinates of two diagonally opposite corners of the rectangle (the rectangle will
include its upper and left edges but not its lower or right edges). After the coordinates
there may be any number of option-value pairs, each of which sets one of the configuration
options for the item. These same option-value pairs may be used in itemconfigure widget
commands to change the item's configuration. A rectangle item becomes the current item
when the mouse pointer is over any part that is painted or (when fully transparent) that
would be painted if both the -fill and -outline options were non-empty.
The following standard options are supported by rectangles:
-dash -activedash
-disableddash -dashoffset
-fill -activefill
-disabledfill -offset
-outline -activeoutline
-disabledoutline -outlineoffset
-outlinestipple -activeoutlinestipple
-disabledoutlinestipple -stipple
-activestipple -disabledstipple
-state -tags
-width -activewidth
-disabledwidth
There are no rectangle-specific options.
TEXT ITEMS
A text item displays a string of characters on the screen in one or more lines. Text
items support indexing, editing and selection through the dchars widget command, the focus
widget command, the icursor widget command, the index widget command, the insert widget
command, and the select widget command. Text items are created with widget commands of
the following form:
pathName create text x y ?option value ...?
pathName create text coordList ?option value ...?
The arguments x and y or coordList (which must have two elements) specify the coordinates
of a point used to position the text on the display (see the options below for more
information on how text is displayed). After the coordinates there may be any number of
option-value pairs, each of which sets one of the configuration options for the item.
These same option-value pairs may be used in itemconfigure widget commands to change the
item's configuration. A text item becomes the current item when the mouse pointer is over
any part of its bounding box.
The following standard options are supported by text items:
-anchor -fill
-activefill -disabledfill
-stipple -activestipple
-disabledstipple -state
-tags
The following extra options are supported for text items:
-angle rotationDegrees
RotationDegrees tells how many degrees to rotate the text anticlockwise about the │
positioning 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(3tk), font(3tk), image(3tk), scrollbar(3tk)
KEYWORDS
canvas, widget