Pad++ Programmer's Guide

INTRODUCTION

Pad++ is a structured graphics widget for Tcl/Tk that features zooming. It adds scale, as a first class parameter to all items, as well as mechanisms for navigation through the multi-scale space of the Pad++ widget. Pad++ provides an alternative to the Canvas widget in Tk. The syntax used to interact with a Pad++ widget is similar to the syntax used to interact with a Tk Canvas. Pad++ has special mechanisms to maintain efficiency for large numbers of graphical items, and also supports special item types such as HTML and portals. While it does not offer all of the features of a Canvas, Pad++ offers several extras.

Pad++ widgets implement structured, multi-scale graphics such as rectangles, lines, text, and images. These items can be manipulated (e.g. moved or re-colored) and/or associated with commands using event bindings. This is similar to the way that the Tk bind command uses events to associate commands with widgets. For example, a particular command/script may be associated with the <Button-1> event. This command/script is then invoked whenever button 1 is pressed with the mouse cursor over a particular item (or items).

Pad++ is connected to the Tcl scripting language. This provides a high-level interface to its complex graphics and interactions. While Tcl runs slowly, it is used as a glue language for rapidly creating interfaces and putting them together. The actual interaction and rendering on Pad++ widgets are performed by the Pad++ substrate (written in C++). This approach allows people to develop applications for Pad++ at a high level while avoiding the complexities inherent in this type of system. Pad++ also supports Scheme as an alternative to Tcl.

Keywords
Availability
Running Pad++
Startup Files

Pad++ Programmer's Guide - 10 JUN 1996

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