<?xml version="1.0" encoding="UTF-8"?>

<appendix id="differences">

<title>Differences between FOX and FXRuby</title>

<para>The FXRuby API follows the FOX API very closely and for the most part,

you should be able to use the standard FOX class documentation as a

reference. In some cases, however, fundamental differences between Ruby and

C++ necessitated slight changes in the API. For some other cases, FOX

classes were enhanced to take advantage of Ruby language features (such as

iterators). The purpose of this chapter is to identify some of the

differences between the C++ and Ruby interfaces to FOX.</para>

<para>One difference that should be easy to cope with is the substitution of

Ruby Strings for FXStrings. Any function that would normally expect an

<type>FXString</type> input argument insteads takes a Ruby String.

Similarly, functions that would return an <type>FXString</type> will instead

return a Ruby string. For functions that would normally accept a

<constant>NULL</constant> or empty string argument, just pass

<constant>nil</constant> or an empty string ("").</para>

<simplesect>

<title>Functions that expect arrays of objects</title>

<para>One common pattern in FOX member function argument lists is to

expect a pointer to an array of values, followed by an integer indicating

the number of values in the array. This of course isn't necessary in Ruby,

where <classname>Array</classname> objects "know" their lengths. As a

result, functions such as

<methodname>FXWindow::acquireClipboard()</methodname>, whose C++

declaration looks like this:</para>

<programlisting format="linespecific">FXbool acquireClipboard(const FXDragType *types, FXuint numTypes);</programlisting>

<para>are called from Ruby code by passing in a single

<classname>Array</classname> argument, e.g.</para>

<programlisting format="linespecific">myWindow.acquireClipboard(typesArray)</programlisting>

</simplesect>

<simplesect>

<title>Functions that return values by reference</title>

<para>Many FOX methods take advantage of the C++ language feature of

returning values by reference. For example, the

<methodname>getCursorPos()</methodname> member function for class

<classname>FXWindow</classname> has the declaration:</para>

<programlisting format="linespecific">FXint getCursorPos(FXint&amp; x, FXint&amp; y, FXint&amp; buttons) const;</programlisting>

<para>which indicates that the function takes references to three integers

(x, y and buttons). To call this function from a C++ program, you'd write

code like this:</para>

<programlisting>FXint x, y;

FXuint buttons;

if (window-&gt;getCursorPosition(x, y, buttons))

fprintf(stderr, "Current position is (%d, %d)\n", x, y);</programlisting>

<para>Since this idiom doesn't translate well to Ruby, some functions'

interfaces have been slightly modified. For example, the FXRuby

implementation of <methodname>getCursorPos()</methodname> returns the

three values as an <classname>Array</classname>, e.g.:</para>

<programlisting format="linespecific">x, y, buttons = aWindow.getCursorPos()</programlisting>

<para>The following table shows how these kinds of functions are

implemented in FXRuby:</para>

<informaltable>

<tgroup cols="2">

<thead>

<row>

<entry align="center">Instance Method</entry>

<entry align="center">Return Value</entry>

</row>

</thead>

<tbody>

<row>

<entry><methodname>FXDial#range</methodname></entry>

<entry>Returns a <classname>Range</classname> instance.</entry>

</row>

<row>

<entry><methodname>FXDial#range=(aRange)</methodname></entry>

<entry>Accepts a <classname>Range</classname> instance as its

input.</entry>

</row>

<row>

<entry><methodname>FXFontDialog#fontSelection</methodname></entry>

<entry>Returns the <classname>FXFontDesc</classname>

instance</entry>

</row>

<row>

<entry><methodname>FXFontSelector#fontSelection</methodname></entry>

<entry>Returns the <classname>FXFontDesc</classname>

instance</entry>

</row>

<row>

<entry><methodname>FXGLObject#bounds(range)</methodname></entry>

<entry>Takes an <classname>FXRange</classname> instance as its

input and returns a (possibly modified)

<classname>FXRange</classname> instance.</entry>

</row>

<row>

<entry><methodname>FXGLViewer#eyeToScreen(eye)</methodname></entry>

<entry>Takes an array of eye coordinates (floats) as its input and

returns the screen point coordinate as an array of integers [sx,

sy]</entry>

</row>

<row>

<entry><methodname>FXGLViewer#getBoreVector(sx,

sy)</methodname></entry>

<entry>Returns the endpoint and direction vector as an array of

arrays [point, dir]</entry>

</row>

<row>

<entry><methodname>FXGLViewer#light</methodname></entry>

<entry>Returns a <classname>FXLight</classname> instance</entry>

</row>

<row>

<entry><methodname>FXGLViewer#viewport</methodname></entry>

<entry>Returns an <classname>FXViewport</classname>

instance.</entry>

</row>

<row>

<entry><methodname>FXPrinterDialog#printer</methodname></entry>

<entry>Returns the <classname>FXPrinter</classname>

instance</entry>

</row>

<row>

<entry><methodname>FXScrollArea#position</methodname></entry>

<entry>Returns the position as an array of integers [x, y]</entry>

</row>

<row>

<entry><methodname>FXSlider#range</methodname></entry>

<entry>Returns a <classname>Range</classname> instance.</entry>

</row>

<row>

<entry><methodname>FXSlider#range=(aRange)</methodname></entry>

<entry>Accepts a <classname>Range</classname> instance as its

input.</entry>

</row>

<row>

<entry><methodname>FXSpinner#range</methodname></entry>

<entry>Returns a <classname>Range</classname> instance.</entry>

</row>

<row>

<entry><methodname>FXSpinner#range=(aRange)</methodname></entry>

<entry>Accepts a <classname>Range</classname> instance as its

input.</entry>

</row>

<row>

<entry><methodname>FXText#appendText(text,

notify=false)</methodname></entry>

<entry>Append text to the end of the buffer.</entry>

</row>

<row>

<entry><methodname>FXText#appendStyledText(text, style=0,

notify=false)</methodname></entry>

<entry>Append styled text to the end of the buffer.</entry>

</row>

<row>

<entry><methodname>FXText#extractText(pos, n)</methodname></entry>

<entry>Extracts <emphasis>n</emphasis> characters from the buffer

beginning at position <emphasis>pos</emphasis> and returns the

result as a String.</entry>

</row>

<row>

<entry><methodname>FXText#extractStyle(pos,

n)</methodname></entry>

<entry>Extracts <emphasis>n</emphasis> style characters from the

buffer beginning at position <emphasis>pos</emphasis> and returns

the result as a String.</entry>

</row>

<row>

<entry><methodname>FXText#insertText(pos, text,

notify=false)</methodname></entry>

<entry>Insert <emphasis>text</emphasis> at position

<emphasis>pos</emphasis> in the buffer.</entry>

</row>

<row>

<entry><methodname>FXText#insertStyledText(pos, text, style=0,

notify=false)</methodname></entry>

<entry>Insert <emphasis>text</emphasis> at position

<emphasis>pos</emphasis> in the buffer.</entry>

</row>

<row>

<entry><methodname>FXText#replaceText(pos, m, text,

notify=false)</methodname></entry>

<entry>Replace <emphasis>m</emphasis> characters at

<emphasis>pos</emphasis> by <emphasis>text</emphasis>.</entry>

</row>

<row>

<entry><methodname>FXText#replaceStyledText(pos, m, text, style=0,

notify=false)</methodname></entry>

<entry>Replace <emphasis>m</emphasis> characters at

<emphasis>pos</emphasis> by <emphasis>text</emphasis>.</entry>

</row>

<row>

<entry><methodname>FXText#setDelimiters(delimiters)</methodname></entry>

<entry>Change delimiters of words (<emphasis>delimiters</emphasis>

is a string).</entry>

</row>

<row>

<entry><methodname>FXText#getDelimiters()</methodname></entry>

<entry>Return word delimiters as a string.</entry>

</row>

<row>

<entry><methodname>FXWindow#cursorPosition</methodname></entry>

<entry>Returns an array of integers [x, y, buttons]</entry>

</row>

<row>

<entry><methodname>FXWindow#translateCoordinatesFrom(window, x,

y)</methodname></entry>

<entry>Returns the translated coordinates as an array [x,

y]</entry>

</row>

<row>

<entry><methodname>FXWindow#translateCoordinatesTo(window, x,

y)</methodname></entry>

<entry>Returns the translated coordinates as an array [x,

y]</entry>

</row>

</tbody>

</tgroup>

</informaltable>

</simplesect>

<simplesect>

<title>Iterators</title>

<para>Several classes have been extended with an

<methodname>each</methodname> method to provide Ruby-style iterators.

These classes include <classname>FXComboBox</classname>,

<classname>FXGLGroup</classname>, <classname>FXHeader</classname>,

<classname>FXIconList</classname>, <classname>FXList</classname>,

<classname>FXListBox</classname>, <classname>FXTreeItem</classname>,

<classname>FXTreeList</classname> and

<classname>FXTreeListBox</classname>. These classes also mix-in Ruby's

<classname>Enumerable</classname> module so that you can take full

advantage of the iterators.</para>

<para>The block parameters passed to your code block vary depending on the

class. For example, iterating over an <classname>FXList</classname>

instance yields <classname>FXListItem</classname> parameters:</para>

<programlisting format="linespecific">aList.each { |aListItem|

puts "text for this item = #{aListItem.getText()}"

}</programlisting>

<para>whereas iterating over an <classname>FXComboBox</classname> instance

yields two parameters, the item text (a string) and the item data:</para>

<programlisting format="linespecific">aComboBox.each { |itemText, itemData|

puts "text for this item = #{itemText}"

}</programlisting>

<para>The following table shows the block parameters for each of these

classes' iterators:</para>

<informaltable>

<tgroup cols="2">

<thead>

<row>

<entry align="center">Class</entry>

<entry align="center">Block Parameters</entry>

</row>

</thead>

<tbody>

<row>

<entry><classname>FXComboBox</classname></entry>

<entry>the item text (a string) and user data</entry>

</row>

<row>

<entry><classname>FXGLGroup</classname></entry>

<entry>an <classname>FXGLObject</classname> instance</entry>

</row>

<row>

<entry><classname>FXHeader</classname></entry>

<entry>an <classname>FXHeaderItem</classname> instance</entry>

</row>

<row>

<entry><classname>FXIconList</classname></entry>

<entry>an <classname>FXIconItem</classname> instance</entry>

</row>

<row>

<entry><classname>FXList</classname></entry>

<entry>an <classname>FXListItem</classname> instance</entry>

</row>

<row>

<entry><classname>FXListBox</classname></entry>

<entry>the item text (a string), icon (an

<classname>FXIcon</classname> instance) and user data</entry>

</row>

<row>

<entry><classname>FXTreeItem</classname></entry>

<entry>an <classname>FXTreeItem</classname> instance</entry>

</row>

<row>

<entry><classname>FXTreeList</classname></entry>

<entry>an <classname>FXTreeItem</classname> instance</entry>

</row>

<row>

<entry><classname>FXTreeListBox</classname></entry>

<entry>an <classname>FXTreeItem</classname> instance</entry>

</row>

</tbody>

</tgroup>

</informaltable>

</simplesect>

<simplesect>

<title>Attribute Accessors</title>

<para>FOX strictly handles access to all object attributes through member

functions, e.g. <methodname>setBackgroundColor</methodname> and

<methodname>getBackgroundColor</methodname> or

<methodname>setText</methodname> and <methodname>getText</methodname>.

FXRuby exposes all of these functions but also provides aliases that look

more like regular Ruby attribute accessors. The names for these accessors

are based on the FOX method names; for example,

<methodname>setBackgroundColor</methodname> and

<methodname>getBackgroundColor</methodname> are aliased to

<methodname>backgroundColor=</methodname> and

<methodname>backgroundColor</methodname>, respectively.</para>

<para>In many cases these aliases allow you to write more compact and

legible code. For example, consider this code snippet:</para>

<programlisting format="linespecific">aLabel.setText(aLabel.getText() + " (modified)")</programlisting>

<para>Now consider a different code snippet, using the aliased accessor

method names:</para>

<programlisting format="linespecific">aLabel.text += " (modified)"</programlisting>

<para>While these two are functionally equivalent, the latter is a bit

easier to read and understand at first glance.</para>

</simplesect>

<simplesect>

<title>Message Passing</title>

<para>FOX message maps are implemented as static C++ class members. With

FXRuby, you just associate messages with message handlers in the class

<methodname>initialize</methodname> method using the

<methodname>FXMAPFUNC()</methodname>,

<methodname>FXMAPTYPE()</methodname>,

<methodname>FXMAPTYPES()</methodname> or

<methodname>FXMAPFUNCS()</methodname> methods. See almost any of the

example programs for examples of how this is done.</para>

<para>As in C++ FOX, the last argument passed to your message handler

functions contains message-specific data. For instance, all

<constant>SEL_PAINT</constant> messages pass an

<classname>FXEvent</classname> object through this argument to give you

some information about the size of the exposed rectangle. On the other

hand, a <constant>SEL_COMMAND</constant> message from an

<classname>FXHeader</classname> object passes the index of the selected

header item through this argument. Instead of guessing what's in this last

argument, your best bet is to instead invoke a member function on the

sending object to find out what you need, instead of relying on the data

passed through this pointer. For example, if you get a

<constant>SEL_COMMAND</constant> message from an

<classname>FXColorWell</classname> object, the data passed through that

last argument is supposed to be the new RGB color value. Instead of trying

to interpret the argument's contents, just turn around and call the color

well's <methodname>getRGBA()</methodname> member function to retrieve its

color. Similarly, if you get a <constant>SEL_COMMAND</constant> message

from a tree list, call its <methodname>getCurrentItem()</methodname>

method to find out which item was selected.</para>

</simplesect>

<simplesect>

<title>Catching Operating System Signals</title>

<para>The <methodname>FXApp#addSignal</methodname> and

<methodname>FXApp#removeSignal</methodname> methods have been enhanced to

accept either a string or integer as their first argument. If it's a

string (e.g. "SIGINT" or just "INT") the code will determine the

corresponding signal number for you (similar to the standard Ruby

library's <methodname>Process.kill</methodname> module method). For

examples of how to use this, see the <filename>datatarget.rb</filename> or

<filename>imageviewer.rb</filename> example programs.</para>

</simplesect>

<simplesect>

<title>Support for Multithreaded Applications</title>

<para>There is some support for multithreaded FXRuby applications, but

it's not wonderful. The current implementation does what is also done in

Ruby/GTK; it turns over some idle processing time to the Ruby thread

scheduler to let other threads do their thing. As I learn more about

Ruby's threading implementation I may try something different, but this

seems to work OK for now. For a simple example, see the

<filename>groupbox.rb</filename> example program, in which the clock label

that appears in the lower right-hand corner is continuously updated (by a

separate thread).</para>

<para>If you suspect that FXRuby's threads support is interfering with

your application's performance, you may want to try tweaking the amount of

time that the main application thread "sleeps" during idle processing; do

this by setting the <classname>FXApp</classname> object's

<structfield>sleepTime</structfield> attribute. The default value for

<structfield>FXApp#sleepTime</structfield> is 100 milliseconds. You can

also disable the threads support completely by calling

<methodname>FXApp#threadsEnabled=false</methodname> (and subsequently

re-enable it with

<methodname>FXApp#threadsEnabled=true</methodname>).</para>

</simplesect>

<simplesect>

<title>Keyword-Style Arguments</title>

<para>FXRuby 1.6.5 introduced preliminary, experimental support for using

keyword-style arguments in FXRuby method calls. The current implementation

of this feature only works for class constructors (i.e. the "new" class

methods), but the intent is to gradually extend this feature so that it

covers all FXRuby methods.</para>

<para>What this means in practice is that for calls to methods that have

one or more optional arguments, you can replace all of the optional

arguments with a hash that sets only the values for which the default

isn't appropriate. So, for example, consider a typical call to

<methodname>FXMainWindow.new</methodname>:</para>

<programlisting>main = FXMainWindow.new(app, "Title Goes Here", nil, nil, DECOR_ALL, 0, 0, 800, 600)</programlisting>

<para>In this case, the programmer wants to set the initial window width

and height to 800 and 600. In order to do that (with the current release

of FXRuby), however, she's required to fill in all of the optional

arguments in between the window title string and the width and height

values. As anyone who's worked with FXRuby for any amount of time will

tell you, it's easy to accidentally leave out one of those intermediate

arguments and it can be difficult to figure out what's wrong

afterwards.</para>

<para>Now consider how this method call could be written using the new

keyword arguments support. First, the programmer would need to require the

keyword arguments library:</para>

<programlisting>require 'fox16/kwargs'</programlisting>

<para>Then she would look up the API documentation for the

<methodname>FXMainWindow#initialize</methodname> method (e.g. <ulink

url="http://www.fxruby.org/doc/api/classes/Fox/FXMainWindow.html">here</ulink>)

and see that the names of the width and height arguments are, in fact,

"width" and "height". Armed with that information, she would be able to

rewrite the previous code as:</para>

<programlisting>main = FXMainWindow.new(app, "Title Goes Here", :width =&gt; 800, :height =&gt; 600)</programlisting>

<para>Here, the programmer has omitted the intermediate optional arguments

(thus accepting their default values) and specified only the width and

height values. This code is obviously a lot more readable and

maintainable.</para>

<para>It is important to observe the difference between required and

optional arguments when using this feature. If the API documentation for a

particular method doesn't indicate that an argument has a default value,

then it is by definition not an optional argument. So one could

<emphasis>not</emphasis> write the example as, e.g.</para>

<programlisting>main = FXMainWindow.new(app, :width =&gt; 800, :title =&gt; "Title Goes Here", :height =&gt; 600)</programlisting>

<para>This example is incorrect because the title argument is required,

and it must be the second argument in the call. Obviously, this means that

the optional arguments in a method call (if they're specified) will always

follow all of the required arguments.</para>

<para>Finally, note that the keyword arguments feature has been

implemented so that it's backwards-compatible with the original positional

arguments scheme (or it's intended to be, at any rate). What that means is

that you can immediately start making use of this feature in your existing

code, even if you don't have time to update all of the method calls to use

keyword arguments.</para>

</simplesect>

<simplesect>

<title>Debugging Tricks</title>

<para>As a debugging tool, you can optionally catch exceptions raised in

message handlers. To turn on this feature, call the

<methodname>setIgnoreExceptions(true)</methodname> module method. When

this is enabled, any exceptions raised in message handler functions will

cause a standard stack trace to be dumped to the standard output, but then

your application will, for better or worse, proceed normally. Thanks to

Ted Meng for this suggestion.</para>

</simplesect>

</appendix>