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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 background, 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 view-port viewport
              port 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. -grid-cellcommand.
              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 operated 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 lifecycle 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)