NAME

canvas - Create and manipulate canvas widgets

SYNOPSIS

canvas pathName ?options?

STANDARD OPTIONS

-background	-borderwidth	-cursor
-highlightbackground	-highlightcolor	-highlightthickness
-insertbackground	-insertborderwidth	-insertofftime
-insertontime	-insertwidth	-relief
-selectbackground	-selectborderwidth	-selectforeground
-takefocus	-xscrollcommand	-yscrollcommand

See the options manual entry for details on the standard options.

WIDGET-SPECIFIC OPTIONS

[-closeenough 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. [-confine 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. [-height 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. [-scrollregion 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. [-state 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. [-width 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. [-xscrollincrement xScrollIncrement] 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. [-yscrollincrement yScrollIncrement] 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 raise and lower Tk commands instead.

ITEM IDS AND TAGS

Items in a canvas widget may be named in either of two ways: by id or by tag. Each item has a unique identifying number, which is assigned to that item when it is created. The id of an item never changes and id numbers are never re-used within the lifetime of a canvas widget.

Each item may also have any number of tags associated with it. A tag is just a string of characters, and it may take any form except that of an integer. For example, “x123” is OK but “123” is not. The same tag may be associated with many different items. This is commonly done to group items in 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)}

      .c find withtag {a^b}

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.

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 then 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 ...?

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:

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.

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.

pathName create type x y ?x y ...? ?option value ...?

pathName create type coordList ?option value ...?

Create a new item in pathName of type type. The exact format of the arguments after type depends on type, but usually they consist of the coordinates for one or more points, followed by specifications for zero or more item options. See the subsections on individual item types below for more on the syntax of this command. This command returns the id for the new item.

pathName dchars tagOrId first ?last?

For each item given by tagOrId, delete the characters, or coordinates, in the range given by first and last, inclusive. If some of the items given by tagOrId do not support indexing operations then they ignore dchars. Text items interpret first and last as indices to a character, line and polygon items interpret them indices to a coordinate (an x,y pair). Indices are described in INDICES above. If last is omitted, it defaults to first. This command returns an empty string.

pathName delete ?tagOrId tagOrId ...?

Delete each of the items given by each tagOrId, and return an empty string.

pathName dtag tagOrId ?tagToDelete?

For each of the items given by tagOrId, delete the tag given by tagToDelete from the list of those associated with the item. If an item does not have the tag tagToDelete then the item is unaffected by the command. If tagToDelete is omitted then it defaults to tagOrId. This 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.

pathName gettags tagOrId

Return a list whose elements are the tags associated with the item given by tagOrId. If tagOrId refers to more than one item, then the tags are returned from the first such item in the display list. If tagOrId does not refer to any items, or if the item contains no tags, then an empty string is returned.

pathName icursor tagOrId index

Set the position of the insertion cursor for the item(s) given by tagOrId to just before the character whose position is given by index. If some or all of the items given by tagOrId do not support an insertion cursor then this command has no effect on them. See INDICES above for a description of the legal forms for index. Note: the insertion cursor is only displayed in an item if that item currently has the keyboard focus (see the widget command focus, below), but the cursor position may be set even when the item does not have the focus. This command returns an empty string.

pathName index tagOrId index

This command returns a decimal string giving the numerical index within tagOrId corresponding to index. Index gives a textual description of the desired position as described in INDICES above. Text items interpret index as an index to a character, line and polygon items 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 and lower commands, not the raise and lower widget commands for canvases. This command returns an empty string.

pathName move tagOrId xAmount yAmount

Move each of the items given by tagOrId in the canvas coordinate space by adding xAmount to the x-coordinate of each point associated with the item and yAmount to the y-coordinate of each point associated with the item. This command returns an empty string.

pathName postscript ?option value option value ...?

Generate a Postscript representation for part or all of the canvas. If the -file option is specified then the Postscript is written to a file and an empty string is returned; otherwise the Postscript is returned as the result of the command. If the interpreter that owns the canvas is marked as safe, the operation will fail because safe interpreters are not allowed to write files. If the -channel option is specified, the argument denotes the name of a channel already opened for writing. The Postscript is written to that channel, and the channel is left open for further writing at the end of the operation. The Postscript is created in 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:

pathName raise tagOrId ?aboveThis?

Move all of the items given by tagOrId to a new position in the display list just after the item given by aboveThis. If tagOrId refers to more than one item then all are moved but the relative order of the moved items will not be changed. AboveThis is a tag or id; if it refers to more than one item then the last (topmost) of these items in the display list is used as the destination location for the moved items. Note: this command has no effect on window items. Window items always obscure other item types, and the stacking order of window items is determined by the raise and lower commands, not the raise and lower widget commands for canvases. This command returns an empty string.

pathName scale tagOrId xOrigin yOrigin xScale yScale

Rescale all of the items given by tagOrId in canvas coordinate space. XOrigin and yOrigin identify the origin for the scaling operation and xScale and yScale identify the scale factors for x- and y-coordinates, respectively (a scale factor of 1.0 implies no change to that coordinate). For each of the points defining each item, the x-coordinate is adjusted to change the distance from xOrigin by a factor of xScale. Similarly, each y-coordinate is adjusted to change the distance from yOrigin by a factor of yScale. This command returns an empty string.

pathName scan option args

This command is used to implement scanning on canvases. It has two forms, depending on option:

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 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 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:

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.

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 option value ...?
pathName create arc coordList ?option value option value ...?

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

-extent degrees

Specifies the size of the angular range occupied by the arc. The arc's range extends for degrees degrees counter-clockwise from the starting angle given by the -start option. Degrees may be negative. If it is greater than 360 or less than -360, then degrees modulo 360 is used as the extent.

-start degrees

Specifies the beginning of the angular range occupied by the arc. Degrees is given in units of degrees measured counter-clockwise from the 3-o'clock position; it may be either positive or negative.

-style type

Specifies how to draw the arc. If type is pieslice (the default) then the arc's region is defined by a section of the oval's perimeter plus two line segments, one between the center of the oval and each end of the perimeter section. If type is chord then the arc's region is defined by a section of the oval's perimeter plus a single line segment connecting the two end points of the perimeter section. If type is arc then the arc's region consists of a section of the perimeter alone. In this last case the -fill option is ignored.

BITMAP ITEMS

Items of type bitmap appear on the display as images with two colors, foreground and background. Bitmaps are created with widget commands of the following form:

pathName create bitmap x y ?option value option value ...?
pathName create bitmap coordList ?option value option value ...?

The following standard options are supported by bitmaps:

-state
-tags

-anchor anchorPos

AnchorPos tells how to position the bitmap relative to the positioning point for the item; it may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then the bitmap is centered on the point; if anchorPos is n then the bitmap will be drawn so that its top center point is at the positioning point. This option defaults to center.

-background color

-activebackground bitmap

-disabledbackground bitmap

Specifies the color to use for each of the bitmap's “0” valued pixels in its normal, active and disabled states. Color may have any of the forms accepted by Tk_GetColor. If this option is not specified, or if it is specified as an empty string, then nothing is displayed where the bitmap pixels are 0; this produces a transparent effect.

-bitmap bitmap

-activebitmap bitmap

-disabledbitmap bitmap

Specifies the bitmaps to display in the item in its normal, active and disabled states. Bitmap may have any of the forms accepted by Tk_GetBitmap.

-foreground color

-activeforeground bitmap

-disabledforeground bitmap

Specifies the color to use for each of the bitmap's “1” valued pixels in its normal, active and disabled states. Color may have any of the forms accepted by Tk_GetColor and defaults to black.

IMAGE ITEMS

Items of type image are used to display images on a canvas. Images are created with widget commands of the following form:

pathName create image x y ?option value option value ...?
pathName create image coordList ?option value option value ...?

The following standard options are supported by images:

-state
-tags

-anchor anchorPos

AnchorPos tells how to position the image relative to the positioning point for the item; it may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then the image is centered on the point; if anchorPos is n then the image will be drawn so that its top center point is at the positioning point. This option defaults to center.

-image name

-activeimage name

-disabledimage name

Specifies the name of the images to display in the item in is normal, active and disabled states. This image must have been created previously with the image create command.

LINE ITEMS

Items of type line appear on the display as one or more connected line segments or curves. Line items support coordinate indexing operations using the canvas widget commands: dchars, index, insert. Lines are created with widget commands of the following form:

pathName create line x1 y1... xn yn ?option value option value ...?
pathName create line coordList ?option value option value ...?

The following standard options are supported by lines:

-dash
-activedash
-disableddash
-dashoffset
-fill
-activefill
-disabledfill
-stipple
-activestipple
-disabledstipple
-state
-tags
-width
-activewidth
-disabledwidth

-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_GetCapStyle (bevel, miter, or round). If this option is not specified then it defaults to round. If the line only contains two points then this option is irrelevant.

-smooth smoothMethod

smoothMethod must have one of the forms accepted by Tcl_GetBoolean or a line smoothing method. Only true and raw are supported in the core (with bezier being an alias for true), but more can be added at runtime. If a boolean false value or empty string is given, no smoothing is applied. A boolean truth value assumes true smoothing. If the smoothing method is true, this indicates that the line should be drawn as a curve, rendered as a set of quadratic splines: one spline is drawn for the first and second line segments, one for the second and third, and so on. Straight-line segments can be generated within a curve by duplicating the end-points of the desired line segment. If the smoothing method is raw, this indicates that the line should also be drawn as a curve but where the list of coordinates is such that the first 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 option value ...?
pathName create oval coordList ?option value option value ...?

The following standard options are supported by ovals:

-dash
-activedash
-disableddash
-dashoffset
-fill
-activefill
-disabledfill
-offset
-outline
-activeoutline
-disabledoutline
-outlineoffset
-outlinestipple
-activeoutlinestipple
-disabledoutlinestipple
-stipple
-activestipple
-disabledstipple
-state
-tags
-width
-activewidth
-disabledwidth

POLYGON ITEMS

Items of type polygon appear as polygonal or curved filled regions on the display. Polygon items support coordinate indexing operations using the canvas widget commands: dchars, index, insert. Polygons are created with widget commands of the following form:

pathName create polygon x1 y1 ... xn yn ?option value option value ...?
pathName create polygon coordList ?option value option value ...?

The following standard options are supported by polygons:

-dash
-activedash
-disableddash
-dashoffset
-fill
-activefill
-disabledfill
-offset
-outline
-activeoutline
-disabledoutline
-outlinestipple
-activeoutlinestipple
-disabledoutlinestipple
-stipple
-activestipple
-disabledstipple
-state
-tags
-width
-activewidth
-disabledwidth

-joinstyle style

Specifies the ways in which joints are to be drawn at the vertices of the outline. Style may have any of the forms accepted by Tk_GetCapStyle (bevel, miter, or round). If this option is not specified then it defaults to round.

-smooth boolean

Boolean must have one of the forms accepted by Tcl_GetBoolean or a line smoothing method. Only true and raw are supported in the core (with bezier being an alias for true), but more can be added at runtime. If a boolean false value or empty string is given, no smoothing is applied. A boolean truth value assumes true smoothing. If the smoothing method is true, this indicates that the polygon should be drawn as a curve, rendered as a set of quadratic splines: one spline is drawn for the first and second line segments, one for the second and third, and so on. Straight-line segments can be generated within a curve by duplicating the end-points of the desired line segment. If the smoothing method is raw, this indicates that the polygon should also be drawn as a curve but where the list of coordinates is such that the first 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 option value ...?
pathName create rectangle coordList ?option value option value ...?

The following standard options are supported by rectangles:

-dash
-activedash
-disableddash
-dashoffset
-fill
-activefill
-disabledfill
-offset
-outline
-activeoutline
-disabledoutline
-outlineoffset
-outlinestipple
-activeoutlinestipple
-disabledoutlinestipple
-stipple
-activestipple
-disabledstipple
-state
-tags
-width
-activewidth
-disabledwidth

TEXT ITEMS

A text item displays a string of characters on the screen in one or more lines. Text items support indexing and selection, along with the following text-related canvas widget commands: dchars, focus, icursor, index, insert, select. Text items are created with widget commands of the following form:

pathName create text x y ?option value option value ...?
pathName create text coordList ?option value option value ...?

The following standard options are supported by text items:

-fill
-activefill
-disabledfill
-stipple
-activestipple
-disabledstipple
-state
-tags

-anchor anchorPos

AnchorPos tells how to position the text relative to the positioning point for the text; it may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then the text is centered on the point; if anchorPos is n then the text will be drawn such that the top center point of the rectangular region occupied by the text will be at the positioning point. This option defaults to center.

-font fontName

Specifies the font to use for the text item. FontName may be any string acceptable to Tk_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 option value ...?
pathName create window coordList ?option value option value ...?

The following standard options are supported by window items:

-state
-tags

-anchor anchorPos

AnchorPos tells how to position the window relative to the positioning point for the item; it may have any of the forms accepted by Tk_GetAnchor. For example, if anchorPos is center then the window is centered on the point; if anchorPos is n then the window will be drawn so that its top center point is at the positioning point. This option defaults to center.

-height pixels

Specifies the height to assign to the item's window. Pixels may have any of the forms described in the COORDINATES section above. If this option is not specified, or if it is specified as zero, then the window is given whatever height it requests internally.

-width pixels

Specifies the width to assign to the item's window. Pixels may have any of the forms described in the COORDINATES section above. If this option is not specified, or if it is specified as zero, then the window is given whatever width it requests internally.

-window pathName

Specifies the window to associate with this item. The window specified by pathName must either be a child of the canvas widget or a child of some ancestor of the canvas widget. PathName may not refer to a top-level window.

Note: due to restrictions in the ways that windows are managed, it is not possible to draw other graphical items (such as lines and images) on top of window items. A window item always obscures any graphics that overlap it, regardless of their order in the display list. Also note that window items, unlike other canvas items, are not clipped for display by their containing canvas's border, and are instead clipped by the parent widget of the window specified by the -window option; when the parent widget is the canvas, this means that the window item can overlap the canvas's border.

APPLICATION-DEFINED ITEM TYPES

It is possible for individual applications to define new item types for canvas widgets using C code. See the documentation for Tk_CreateItemType.

BINDINGS

In the current implementation, new canvases are not given any default behavior: you will have to execute explicit Tcl commands to give the canvas its behavior.

CREDITS

Tk's canvas widget is a blatant ripoff of ideas from Joel Bartlett's ezd program. Ezd provides structured graphics in a Scheme environment and preceded canvases by a year or two. Its simple 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