Instructions For Writing Tclets

[ Sun Home | Tcl Home | Tcl Plugin ]

These instructions should be updated shortly for the new version 2.0 features

Here is a cookbook for how to write your first tclet:

The simplest Tk program is shown below:

button .b -text "Hello, world!"
pack .b

Create a file named simple.tcl with this program in it.

---

with the following HTML in it:

Here is my first embedded tclet:

<embed src=simple.tcl width=140 height=30>

That's IT. You're done. This page should look like what you've created above.

Feedback is appreciated! If you want to send in a comment, just email to sunscript-plugin@sunscript.sun.com. All comments are welcome, and email will be acknowledged if you include a reply-to address.

Safe Tcl and Safe Tk

You can test your Tclet by running it in the wish shell; you don't have to run it inside Netscape. However, when you are running in the Tcl plugin you have a restricted set of Tcl commands for security reasons. The following Tcl commands are not available:

• bell - ring terminal bell
• cd - change directory
• clipboard - access CLIPBOARD selection
• exec - run programs
• glob - match file names in a directory
• grab - grab the cursor
• menu - display a menu
• pwd - query current directory
• send - send Tcl commands to other Tk applications
• socket - open a network socket
• tk - set/query Tk application name
• tkwait - block on events. You can use vwait to wait for variables to change.
• toplevel - create toplevel windows.
• wm - window manager control

Stand Alone or Plug In?

You can detect if you are running in the plugin by testing for the existing of the embed_args variable. This is an array whose values come from the <embed> tag in the document. For example, $embed_args(src) contains the name of the Tcl script for the applet. You can put whatever NAME=VALUE pairs you want in the <embed> tag. The Plugin looks at SRC, WIDTH, and HEIGHT. Any others are for your own use.

Other Tcl variables defined especially for the plugin are:

nptcl_version

String describing the plugin version such as "1.0"

nptcl_patchLevel

String describing the plugin patch level, such as "1.0"

Window sizing

The plugin turns off geometry propagation for the main window. All it does is:

pack propagate . false

This helps make the window the same size as the HTML width and height specifiers in the <embed> tag. Tclets you write should still work if they depend on the grid geometry manager, but in that case, you'll have to size the window yourself.

grid propagate . false