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
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 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 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