Extensions to the canvas interface

The Slate adds a number of new methods to the canvas interface. Some of these methods deal exclusively with complex items; others work with both primitive and complex items. Here is an overview.

aspect id ?aspect? ... ?-region?
Return aspect coordinates as a flat x-y list. An aspect is a named point on an item, such as "origin" or "center" or "ne." The aspects of an item depend on its type. If the -region flag is supplied, treat the item as a rectangular item regardless of its real shape. To query legal aspects, call with no argument, and a list of legal aspects will be returned. (Note that the legal aspects are not necessarily constant over the lifetime of an item -- for example, adding a vertex to a polygon will also add an aspect.)

call id method ?val? ...
Call the "method" method on a complex item. All additional arguments are passed to the method.

component id ?component? ?method? ?val? ...
Access components of a complex item. With just the id argument, return a list of components of this item. If component is supplied, return that component. If additional arguments are supplied, call method on the component and return the result.

describe id
Return a string that "describes" an item. This string can be given back to the recreate command to re-create or clone the item.

focusin
Apply the focus to the canvas inside the slate.

interact mode item ?val? ...
This method is the switchboard for a number of interaction commands. The structure of the interaction interface will probably change, but the current set of commands is:

moveto tag x y ?aspect?
Move the point of an item denoted by aspect to the absolute location (x, y). If tag denotes more than one item, treat the set of items as a rectangle. (In this case, aspect must of course be legal for rectangles.) If aspect is omitted, it defaults to center.

picture command ?val? ...
This method is a switchboard for a bunch of commands related to managing the item hierarchy. The set of commands is currently in flux.

recreate description ?-move x y? ?-at x y? ?-coords x0 y0 ... ? ?-in id?
Re-create an item from a string returned by the describe method. The various options allow the item to be created at a different position on the canvas, or as a child of some other item.

region id canvas slate ?x0 y0 x1 y1?
Get or set the region of an item. This is the same as coords, except that it treats every item as though it were rectangular.

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Last updated: 96/12/11, comments to: johnr@eecs.berkeley.edu