The tkdraw script is essentially an interface to the capabilities built in to
tk canvas widgets, packaged as a drawing tool. The general method is to have
two major windows, one a canvas, and one a text window showing the
descripton of the canvas object currently being manipulated as
a set of tcl commands.
Gestural commands on the canvas to locate objects, shape objects,
select objets, or move them, make the appropriate text edits to the
tcl commands in the text window.
Finally, a row of buttons supply miscelaneous menus and operations,
such as interactions with the file system, access to objects by browsing
the drawlist instead of the canvas, common edits such as duplication,
movement, new object creation, and "apply" of changes.
Sets the edit text to the options for the drawing as a whole.
The apply button must be used to commit changes made.
file.clear
Clears the edit text. Useful to do to avoid confusion, or to
prepare to type in commands "by hand" to apply, eg, use
file.clear, then type "exec lpr -Psome_printer << [c postscript]"
and then the apply operation will print the current drawing to
the some_printer postscript printer.
file.new
Clears the canvas, resets the draw list to empty.
file.read
Reads a file containing a drawing in tcl-list format, replacing
the current drawing.
file.include
Reads a file containing a drawing in tcl-list format, adding it to
the current drawing.
file.write
Writes the drawing to a file in tcl-list format.
file.write-ps
Writes the drawing to a file in postscript format. It choses the
filename from the options settings, and replaces any extension with ".ps".
file.write-gif
Writes the drawing to a file in gif format. It chooses the
filename from the options settings, and replaces any extension with
".gif". The PBM toolkit and xwd must be on your $PATH.
file.print
Pipes the canvas to lpr in postscript form.
file.quit
Terminates the tkdraw session. Note, there is no checking to ensure
file write of any canvas changes.
The tcl button executes the current X selection as a tcl script.
This is useful for importint commands, customizations, or configuration
options from other tools.
Pops up a top-level window containing the current drawlist,
so that one can access any of the items for edit without necessarily
knowing where it is on the canvas.
ed.delete-item
Deletes the item currently in the edit buffer from the
canvas and the draw list (but leaves it in the text buffer).
ed.scale-item
Prepares to scale all coordinates of item in the edit buffer
by a given factor; pick an origin, x & y scale factors, and apply
ed.grid
Edits the item currently in the edit buffer, moving all coordinates
in the coordinate list to the next lower multiple of 10. Useful for
precision alignment of points in an object for regular shape, or
for aligning multiple objects.
Presumes that the last four entries in the coordinate line are
movement endpoints, and edits the prior entries. Thus, to move
an object, select it, drag from any point on the object to where
you want that point to land, and do the mov operation.
The apply button is used to commit changes to canvas. The top, dup,
and mov buttons automatically apply, but other edits must be
explicitly applied, or they will not take effect.
There are three gestural idioms supported on the canvas.
Each of them updates the text display.
placement
A single leftclick will add an x,y coordinate pair to the current
object's coordinate list. Thus, to place a bitmap or text object on
the canvas, create it from the new menu, specifiy its bitmap
file or text content, click on the canvas, and execute the apply
button.
rubberbanding
A left drag on the canvas will add two x,y coordinate pairs to the current
object's coordinate list, and during the drag, the current bounding box
and its diagonal track mouse motions. Thus, to create a rectang, oval,
or arc, simply creat it from the new menu, drag out its location on
the canvas, and apply.
Note that this is also used for moving objects. Simply select the
object (see below), drag from where it is to where you want it, and
apply.
selection
A middleclick on the canvas will select the nearest object for
editing. It is also useful if you need prompting for what options
are available on particlar objects. For example, you can create
a line with a plain style, then select the just-created line for
editing, and the options for color, arrow style, edge rounding,
spline curves, and so on, will all be presented.
Note that since there is an "include" option, different drawings can
be combined. Simply selection file.options, choose a filename of an
old drawing with some features you want to reuse, then choose file.include.
Its drawing list will be added to that of the current drawing.
Sometimes, however, it would be easier to snip out only one object or two,
rather than including a compelex drawing and then deleting most of it. In
that case, other possibilities might be easier. One possibility is to bring
up another copy of tkdraw on a file that has an element you wish to snip.
Then, select it for editing and select its text as the X selection.
Finally, go back to the original tkdraw, select file.clear, past in
the text with either ctrl-V or right-click, and hit "top" to insert
it into the local drawing's draw list. Another possibility is to read
the first drawing, save the text into another X window (say, an editor),
read the new drawing, and use clear/paste/top to insert it.
Finally, note that flipping to the drawing options, then applying,
then chosing read or include, can be tedious. You can simply use
file.clear, then type
read-drawing 1 foo
to read in file "foo". Note that "1" as the first argument includes the
file; "0" can be used to overwrite the current drawing.
grouping
Tkdraw doesn't do groups. It's application domain is small
overhead transparencies, HTML pages, and so on, so the draw list usually
doesn't get complicated enough to make it worthwhile in practice
in its user community. But if you've placed a group of objects, and
want to move them all as a group elsewhere, you can save the two x,y
coordinate pairs from a drag into another window, and make them the
current X selection. Then, you can simply choose each of the objects
you wish to move as a group in turn, paste the coordinates in with
a rightclick or ctrl-V, and select move. They will all retain their
precise relative placement on the screen, but moved to a new location.
Also, by storing a group of objects in a file, they can all be
inserted into a drawing as a unit via file.include.
macros
If some arbitrary tcl commands need to be executed for some
portion of a drawing, they could be stored in the "comments" field
of the options, then simply selected and executed with the "tcl" button
to expand them when the drawing is loaded. Eventually, adding a macro
capability to the draw list will be a superior solution, and may also
be a way to get grouping cleanly, but this is still tenative.
Weaknesses currently are lack of groups, the ability to provoke
arbitrary tcl or tk errors by mistyping in the text window, and
no point-and-click file browsing interface.
