Using tcl to Replay Xt Applications

Why ``play'' Xt Applications?

• Automated testing of GUI applications.
• Automated demonstration of GUI applications.
• Scripting language to control Xt Applications cf AppleScript

X support for record/replay

• Preparation of X events.
• Extensions like XTrap allow X event capture.

• Insertion into the X event queue by XSendEvent().

• Capture of X windows as screendumps.
• Comparison of screendumps.

Drawbacks of X approaches

• X events require x, y co-ordinates.
• Moving or resizing windows may invalidate this.
• Screendump comparisons rely on:
  • sizes.
  • co-ordinates.
  • colormaps.
  • structure.

Xt objects

• Xt defines objects called widgets.
  
• Widgets have ``methods'' called ``actions''.
  e.g. Motif PushButton has actions Arm() Disarm() Activate()
  
  
• User level events are mapped into actions.

• Actions call application-level callback functions.

Xt replay system

• Actions define widget methods.
• The Xt function XtCallActionProc() invokes a method.
• A sequence of XtCallActionsProc's allows replay of an Xt application.

Major Xt problems

• Events enter the Xt event queue and are processed by XtAppMainLoop().
• Simulation method must allow queuing, and must allow processing.
• Some actions require event information.
  e.g. The Disarm() action for a Motif PushButton.
• Gadgets don't have actions.

Major simulation language problems

• Use may exceed design: need a full programming language.
• Language must integrate into Xt requirements (rules out C).
• Preference for non-proprietary language.
• Require extensible language.

Tcl - Tool Command Language

• An application-independant command language.
• An extensible language.
• An embeddable language.
• Free.
• Source code availability

Structure of a tcl-enabled application

New tcl command - callActionProc

• Define a new command to the tcl interpreter. callActionProc widget action
  
• Link this to C code that
  • Uses XtNameToWidget() to locate widget.
  • Prepares suitable X event and other parameters.
  • Calls XtCallActionProc()

Event loops

• Failed method: source the file of commands.
  This puts all actions into the queue, and does no processing of events till the end.
• Failed method: parse the file into commands, and run each as a ``work procedure''.
  Won't allow for the delays required for demonstrations.
• Failed method: parse the file into commands, and run each using an Xt timer.
  Can't easily penetrate toplevel of the parse tree, e.g. into loops and procedures.
  
  
  
• Successful method: use the tcl ``trace'' mechanism to call XtProcessEvent().
  Atomic at the tcl level; processes all pending Xt events.

Sample script

Goodies and baddies

• tcl allows for procedural abstraction e.g. proc click {w} { callActionProc $w Arm() sleep 500 callActionProc $w Activate() }
• tcl allows for stress testing e.g. for {set n 0} {$n < 100} {incr n} { testit }
  
• An interface to XtGetValues allows query of widget state e.g. getValues $w \ -width width \ -height height \ set mid_x [expr $width/2] set mid_y [expr $height/2] warpPointer $w $mid_x $mid_y
• The function XtAppAddActionHook() allows recording of actions, but in a less than ideal form.
  
  
• Gadgets are hacks to place load on the application side instead of on the server. Proper handling of them requires regularities not specified by Xt.
• The Motif List widget has non-widget, non-gadget internal structure.
  

Send

• A communication method between X applications. send application tcl-command
• Designed by John Ousterhout for Tk.
• Ported to Xt.
• Builtin to replay library.
• Allows tcl to be used as a scripting language like Apple's AppleScript

Status

• Current version: 1.2
• Available as a library with a single entry point.
• Publically available from ftp.canberra.edu.au

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