canvas::sqmap(n)					      Variations on a canvas						  canvas::sqmap(n)

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NAME

       canvas::sqmap - Canvas with map background based on square tiles

SYNOPSIS

       package require Tcl  8.4

       package require Tk  8.4

       package require snit

       package require uevent::onidle

       package require cache::async

       package require canvas::sqmap  ?0.3.1?

       ::canvas::sqmap pathName ?options?

       canvasName image set cell image

       canvasName image unset cell

       canvasName flush

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DESCRIPTION

       This  package provides an extended canvas widget for the display of maps based on a set of square image tiles. The tiles are the background
       of the canvas, with all other canvas items added always shown in front of them. The number of tiles shown, tile size, and where to get  the
       images to show are all configurable.

API

       ::canvas::sqmap pathName ?options?
	      Creates  the canvas pathName and configures it. The new widget supports all of the options and methods of a regular canvas, plus the
	      options and methods described below.

	      The result of the command is pathName.

   OPTIONS
       -grid-cell-width
	      The value for this option is a non-negative integer. It specifies the width of the cells the background is made up of.

       -grid-cell-height
	      The value for this option is a non-negative integer. It specifies the height of the cells the background is made up of.

       -grid-cell-command
	      The value for this option is a command prefix. It is invoked whenever the canvas needs the image for a specific cell  of	the  back-
	      ground,  with  two additional arguments, the id of the cell, and a command prefix to invoke when the image is ready, or known to not
	      exist.

	      The id of the cell is a 2-element list containing the row and column number of the cell, in this order. The  result  command  prefix
	      (named "$result" in the example below) has to be invoked with either two or three arguments, i.e.

		  $result set	$cellid $image ; # image is known and ready
		  $result unset $cellid        ; # image does not exist

	      This  option  may  be  left  undefined, i.e. the canvas can operate without it. In that case the only images shown in grid cells are
	      those explicitly set with the method image set, see the next section. All other grid cells will simply be empty.

       -viewport-command
	      This option specifies a command prefix to invoke when the viewport of the canvas is changed, to allow users keep track of  where	in
	      the scroll-region we are at all times. This can be used, for example, to drive derivate displays, or to keep items in view by moving
	      them as the viewport moves.

       -image-on-load
	      The value for this option is an image. If specified the image is shown in a cell while the actual image for  that  cell  is  getting
	      loaded through the callback specified by the -grid-cell-command.

       -image-on-unset
	      The value for this option is an image. If specified the image is shown in a cell for which the callback specified by the -grid-cell-
	      command reported that there is no actual image to be shown.

   METHODS
       canvasName image set cell image
	      Invoking this method places the image into the specified cell of the background. The cell is given as a  2-element  list	containing
	      row and column number, in this order.

	      Note that an image is allowed to be associated with and displayed in multiple cells of the canvas.

       canvasName image unset cell
	      Invoking this method declares the specified cell of the background as empty, an existing image shown by this cell will be forgotten.
	      The cell is given as a 2-element list containing row and column number, in this order.

       canvasName flush
	      Invoking this method forces the canvas to completely reload the images for all cells. Do not use this method if the canvas is  oper-
	      ated without a -grid-cell-command, as in that case the canvas will simply forget all images without being able to reload them.

IMAGE OWNERSHIP

       Note  that the canvas does not take ownership of the images it shows in the background. In other words, when we say that the canvas forgets
       an image this means only that the association between a grid cell and shown image is broken. The image is not deleted. Managing the lifecy-
       cle of the images shown by the canvas is responsibility of the user of the canvas.

KEYWORDS

       canvas, cell, grid, image, map, square map, tile

canvas								       0.3.1							  canvas::sqmap(n)