differences.xml

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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&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>