NAME
canvas - Create and manipulate canvas widgets
SYNOPSIS
canvas pathName ?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:-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 path_Name 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 rearrange the order of the display list.
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'' isn't. 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. 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. 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 floatingpoint 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.
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.
INDICES
Text items support the notion of an index for identifying particular positions within the item. Indices are used for commands such as inserting text, deleting a range of characters, 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.
sel.last Refers to the last selected character in the item. If the selection isn't in this item then this form is illegal.
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 isn't 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 then x2 and y1 must be no greater than y2.
overlapping x1 y1 x2 y2
Selects all the items that overlap or are enclosed within the rectangular region given by x1, y1, x2, and y2. X1 must be no greater then x2 and y1 must be no greater than y2.
withtag tagOrId
Selects all the items given by tagOrId.
pathName bbox tagOrId ?tagOrId tagOrId ...? Returns a list with four elements giving an approximate bounding box for all the items named by the tagOrId arguments. The list has the form ``x1 y1 x2 y2'' such that the drawn areas of all the named elements are within the region bounded by x1 on the left, x2 on the right, y1 on the top, and y2 on the bottom. The return value may overestimate the actual bounding box by a few pixels. If no items match any of the tagOrId arguments or if the matching items have empty bounding boxes (i.e. they have nothing to display) then an empty string is returned.
pathName bind tagOrId ?sequence? ?command? This command associates command with all the items given by tagOrId such that whenever the event sequence given by sequence occurs for one of the items the command will be invoked. This widget command is similar to the bind command except that it operates on items in a 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. 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).
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 screen x-coordinate 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 screen y-coordinate 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 ...?
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 ...? 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 in the range given by first and last, inclusive. If some of the items given by tagOrId don't support text operations, then they are ignored. First and last are indices of characters within the item(s) as 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 doesn't have the tag tagTo_Delete 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.
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 doesn't refer to any items, or if none of them support the insertion cursor, then the focus isn't 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 doesn't 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 wasn't 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 doesn't 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 don't 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 doesn't 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. The return value is guaranteed to lie between 0 and the number of characters 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 insertion then string is inserted into the item's text just before the character whose index is beforeThis. 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. 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. 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 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 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.
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 10 times the difference in coordinates. 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 isn't 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 isn't 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 doesn't 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 isn't 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 doesn't 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 -xscrollcom-mand 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. Frac_tion 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 don't 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, only text items provide this support).
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 ...? The arguments x1, y1, x2, and y2 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. The following options are supported for arcs:
pathName create oval x1 y1 x2 y2 ?option value option value ...? The arguments x1, y1, x2, and y2 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. The following options are supported for ovals:
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 ...? The arguments x1, y1, x2, and y2 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. The following options are supported for rectangles:
BINDINGS
In the current implementation, new canvases are not given any default behavior: you'll 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.
KEYWORDS
canvas, widget