'\"
'\" Generated from file 'canvas_sqmap\&.man' by tcllib/doctools with format 'nroff'
'\"
.TH "canvas::sqmap" n 0\&.3\&.1 tklib "Variations on a canvas"
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.SH NAME
canvas::sqmap \- Canvas with map background based on square tiles
.SH SYNOPSIS
package require \fBTcl  8\&.4\fR
.sp
package require \fBTk  8\&.4\fR
.sp
package require \fBsnit \fR
.sp
package require \fBuevent::onidle \fR
.sp
package require \fBcache::async \fR
.sp
package require \fBcanvas::sqmap  ?0\&.3\&.1?\fR
.sp
\fB::canvas::sqmap\fR \fIpathName\fR ?options?
.sp
\fIcanvasName\fR \fBimage set\fR \fIcell\fR \fIimage\fR
.sp
\fIcanvasName\fR \fBimage unset\fR \fIcell\fR
.sp
\fIcanvasName\fR \fBflush\fR
.sp
.BE
.SH 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\&.
.SH API
.TP
\fB::canvas::sqmap\fR \fIpathName\fR ?options?
Creates the canvas \fIpathName\fR and configures it\&. The new widget
supports all of the options and methods of a regular canvas, plus the
options and methods described below\&.
.sp
The result of the command is \fIpathName\fR\&.
.PP
.SS OPTIONS
.TP
\fB-grid-cell-width\fR
The value for this option is a non-negative integer\&. It specifies the
width of the cells the background is made up of\&.
.TP
\fB-grid-cell-height\fR
The value for this option is a non-negative integer\&. It specifies the
height of the cells the background is made up of\&.
.TP
\fB-grid-cell-command\fR
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\&.
.sp
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\&.
.CS


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

.CE
.IP
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 \fBimage set\fR, see the next
section\&. All other grid cells will simply be empty\&.
.TP
\fB-viewport-command\fR
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\&.
.TP
\fB-image-on-load\fR
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 \fB-grid-cell-command\fR\&.
.TP
\fB-image-on-unset\fR
The value for this option is an image\&. If specified the image is shown
in a cell for which the callback specified by the \fB-grid-cell-command\fR
reported that there is no actual image to be shown\&.
.PP
.SS METHODS
.TP
\fIcanvasName\fR \fBimage set\fR \fIcell\fR \fIimage\fR
Invoking this method places the \fIimage\fR into the specified
\fIcell\fR of the background\&. The cell is given as a 2-element list
containing row and column number, in this order\&.
.sp
Note that an image is allowed to be associated with and displayed in
multiple cells of the canvas\&.
.TP
\fIcanvasName\fR \fBimage unset\fR \fIcell\fR
Invoking this method declares the specified \fIcell\fR 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\&.
.TP
\fIcanvasName\fR \fBflush\fR
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 \fB-grid-cell-command\fR, as in that case the canvas will
simply forget all images without being able to reload them\&.
.PP
.SH "IMAGE OWNERSHIP"
Note that the canvas \fIdoes not\fR 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 \fInot\fR
deleted\&. Managing the lifecycle of the images shown by the canvas is
responsibility of the user of the canvas\&.
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fIcanvas\fR of the
\fITklib Trackers\fR [http://core\&.tcl\&.tk/tklib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.SH KEYWORDS
canvas, cell, grid, image, map, square map, tile
