From ace7902333b6f61aab5a6035dbcb222763bff186 Mon Sep 17 00:00:00 2001 From: marha Date: Fri, 6 Nov 2009 06:59:46 +0000 Subject: Added libXaw-1.0.7 --- libXaw/spec/CH7.intro | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 99 insertions(+) create mode 100644 libXaw/spec/CH7.intro (limited to 'libXaw/spec/CH7.intro') diff --git a/libXaw/spec/CH7.intro b/libXaw/spec/CH7.intro new file mode 100644 index 000000000..7aaa1896b --- /dev/null +++ b/libXaw/spec/CH7.intro @@ -0,0 +1,99 @@ +.LP +.bp +.if e .bp \" make sure we break on an odd page. +\& +.sp 1 +.ce 5 +\s+1\fBChapter 7\fP\s-1 + +\s+1\fBCreating New Widgets (Subclassing)\fP\s-1 + +\s+1Written By: Ralph Swick\s-1 +.sp 2 +.nr H1 7 +.nr H2 0 +.nr H3 0 +.nr H4 0 +.nr H5 0 +.na +.LP +.XS +Chapter 7 - Creating New Widgets (Subclassing) +.XE +.IN "subclassing" "" "@DEF@" +.IN "creating new widgets" "" "@DEF@" +.LP +Although the task of creating a new widget may at first appear a little +daunting, there is a basic simple pattern that all widgets follow. The +Athena Widget library contains a special widget called the +\fITemplate\fP widget that is intended to assist the novice widget +programmer in writing a custom widget. +.LP +Reasons for wishing to write a custom widget include: +.IP \(bu 3 +Providing a graphical interface not currently supported by any existing +widget set. +.IP \(bu 3 +Convenient access to resource management procedures to obtain fonts, +colors, etc., even if user customization is not desired. +.IP \(bu 3 +Convenient access to user input dispatch and translation management procedures. +.IP \(bu 3 +Access to callback mechanism for building higher-level application libraries. +.IP \(bu 3 +Customizing the interface or behavior of an existing widget to suit a +special application need. +.IP \(bu 3 +Desire to allow user customization of resources such as fonts, colors, +etc., or to allow convenient re-binding of keys and buttons to internal +functions. +.IP \(bu 3 +Converting a non-Toolkit application to use the Toolkit. +.LP +In each of these cases, the operation needed to create a new widget is +to "subclass" an existing one. If the desired semantics of the new +widget are similar to an existing one, then the implementation of the +existing widget should be examined to see how much work would be +required to create a subclass that will then be +able to share the existing class methods. Much time will be saved in +writing the new widget if an existing widget class Expose, Resize and/or +GeometryManager method can be used by the subclass. +.LP +Note that some trivial uses of a ``bare-bones'' widget may be achieved by +simply creating an instance of the Core +widget. The class variable to use when creating a Core widget is +.PN widgetClass . +The geometry of the Core widget is determined entirely by the parent +widget. +.LP +It is very often the case than an application will have a special need +for a certain set of functions and that many copies of these functions +will be needed. For example, when converting an older application to use +the Toolkit, it may be desirable to have a "Window Widget" class that +might have the following semantics: +.IN "Window widget" +.IN "Core widget" +.IN "widgetClass" +.IP \(bu 3 +Allocate 2 drawing colors in addition to a background color. +.IP \(bu 3 +Allocate a text font. +.IP \(bu 3 +Execute an application-supplied function to handle exposure events. +.IP \(bu 3 +Execute an application-supplied function to handle user input events. +.LP +It is obvious that a completely general-purpose WindowWidgetClass could +be constructed that would export all class methods as callbacks lists, +but such a widget would be very large and would have to choose some +arbitrary number of resources such as colors to allocate. An application +that used many instances of the general-purpose widget would therefore +un-necessarily waste many resources. +.LP +.sp +In this section, an outline will be given of the procedure to follow to +construct a special-purpose widget to address the items listed above. +The reader should refer to the appropriate sections of the \fI\*(xT\fP +for complete details of the material outlined here. Section 1.4 of +the \fI\*(xI\fP should be read in conjunction with this section. +.LP -- cgit v1.2.3