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<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& x, FXint& y, FXint& 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->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 => 800, :height => 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 => 800, :title => "Title Goes Here", :height => 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>