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<table border=0 cellpadding= cellspacing=2 width=100% ><tr><td><a href='http://www.fox-toolkit.org' target=_top><img src='art/foxlogo_small.jpg' border=0></a></td><td width=100% valign=bottom id="HEADLINE"><b>
Documentation: Introduction <A href='introduction.html' target="_top" align=left><font size=-2>[Remove Frame]</font></a>
<br><img src='art/line.gif' width=100% height=1></b></td></tr></table>
<p>
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<ul>
To illustrate the facility with which you can build a FOX application,
we're going to build a few simple FOX applications. The first application
called Scribble. A picture of the Scribble application is shown below:
</ul>
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<p>
<table width=100% cellpadding=0 cellspacing=2><tr><td width=100% valign=bottom id=HEADLINE><b>
Scribble
<br><img src='art/line.gif' width=100% height=1></b></td></tr></table>
<p>
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<ul>
<center>
<p><img SRC="art/scribble.png">
<br>Fig 1. The Scribble Application.
</center>
<p>
Scribble demonstrates how to use the FOX Layout Managers, how to create
Buttons, and how to handle messages. Enough talk, lets start coding!
The very first thing is to include the FOX header files. This is
simple, as there is just one thing you need to include:
<pre>
#include "fx.h"
</pre>
Next, we need a top level Window object, this is a class derived from FXMainWindow.
There is only one Main Window; if you need additional toplevel windows,
you will probably derive those from FXDialogBox or FXTopWindow.
<p>In the case of Scribble, we make a class called ScribbleWindow:
<br>
<pre>
// Event Handler Object
class ScribbleWindow : public FXMainWindow {
// Macro for class hierarchy declarations
FXDECLARE(ScribbleWindow)
</pre>
The first line says <i>ScribbleWindow</i> is derived from <i>FXMainWindow</i>;
FXMainWindow, like most FOX classes, is derived from FXObject. Most
classes you will write in the course of programming with FOX are either
directly or indirectly derived from one single top level class called FXObject.
<p>The macro <i>FXDECLARE(ScribbleWindow)</i> declares a number of member
functions which every object derived from FXObject should have; we've used
a macro as it is always the same, and more convenient to program this way.
<p>Next, we add some member variables to keep track of the various Widgets,
and the drawing color. We also keep a flag to remember if the mouse
was down, and a flag to remember if the canvas is dirty, i.e. has been
scribbled on:
<pre>
private:
FXHorizontalFrame *contents; // Content frame
FXVerticalFrame *buttonFrame; // Button frame
FXCanvas *canvas; // Canvas to draw into
int mdflag; // Mouse button down?
int dirty; // Canvas has been painted?
FXColor drawColor; // Color for the line
</pre>
<br><br>
To satisfy the serialization macro, we need to furnish a default contructor:
<pre>
protected:
ScribbleWindow(){}
</pre>
<p>
FOX handles events from the user through a system of <i>messages</i> sent
to a certain <i>object</i>. In this case, the received of the messages
is the ScribbleWindow class. Thus, we need to add handler member
functions to catch these messages and perform some action in response.
All message handler functions in FOX have the same argument signature:
<p>
<pre>
long onSomeCommand(FXObject* sender,FXSelector sel,void *ptr);
</pre>
Where:
<p>
<ul><b><i>sender</i></b> is the sender object that sent the message to
us.
<br><b><i>sel </i></b>is the selector, a combination of a message type
and message id, which identifies the action being performed.
<br><b><i>ptr </i></b>is a pointer to some event-related data; usually,
this points to the FXEvent structure which contains the event that led
to the message.</ul>
For the Scribble application, we want to handle mouse messages, as
well as messages from the two buttons:
<p>
<pre>
public:
long onPaint(FXObject*,FXSelector,void*);
long onMouseDown(FXObject*,FXSelector,void*);
long onMouseUp(FXObject*,FXSelector,void*);
long onMouseMove(FXObject*,FXSelector,void*);
long onCmdClear(FXObject*,FXSelector,void*);
long onUpdClear(FXObject*,FXSelector,void*);
</pre>
<p>
ScribbleWindow also needs to define some new message ID's. A message
consists of a <b><i>type </i></b>and an <b><i>id</i></b>. The <i>type</i>
defines <i>what</i> has happened; the <i>id</i> identifies the <i>source</i>
of the message. Even though we know the object that sent us the message,
in many cases, we can be sent the same message from different sources,
and the id is much more convenient; so:
<p>
<pre>
public:
enum{
ID_CANVAS=FXMainWindow::ID_LAST,
ID_CLEAR,
ID_LAST
};
</pre>
<p>
We typically define the list of messages some target understands
as an <i>enum</i> type. As the ScribbleWindow class is derived from
FXMainWindow, it also understands all the messages already understood by
the basic FXMainWindow. Our new messages should have different numbers
from those. Rather than counting by hand, we let the compiler worry
about this by simply defining one extra message id with the name <b><i>ID_LAST</i></b>,
a subclass can simply use the ID_LAST of it's base class to start counting
its message id's from; if ever any new message id's are added to the base
class, our own messages are automatically renumbered by the compiler.
<p>We wrap up the remainder of the ScribbleApp class declaration by defining
a constructor and one member function called create():
<p>
<pre>
public:
ScribbleWindow(FXApp* a);
virtual void create();
};
</pre>
<p>
<p><br>In our implementation, the constructor ScribbleWindow will actually
build the GUI. The create() function is a virtual function that is
called by the system. Most FOX Widgets have this create function.
FOX Widgets have a two-stage creation process; first, the client side Widgets
are constructed, using ordinary C++ constructors. Then, once the
whole widget tree is complete, a single call to the application's create()
function will create all the windows for those widgets. This two
step process is needed as the second step may only be executed one the
connecion to the display has been established.
<p>Now, we're ready to implement this new class; in most cases, the previous
code would reside in a header file, while the implementation would be in
a C++ source file, of course. In the case of ScribbleWindow, it is
so simple that we placed everything into one file.
<p>The first thing to do is to define the <b><i>message map</i></b>.
The message map is a simple table that <i>associates </i>a<i> message type,
</i>and<i>
message id </i>to a class's<i> member function.</i> Having a message
map allows us to send any message to any [FXObject-derived] object.
<br>Thus:
<br>
<pre>
FXDEFMAP(ScribbleWindow) ScribbleWindowMap[]={
//________Message_Type_____________________ID_______________Message_Handler_______
FXMAPFUNC(SEL_PAINT, ScribbleWindow::ID_CANVAS,ScribbleWindow::onPaint),
FXMAPFUNC(SEL_LEFTBUTTONPRESS, ScribbleWindow::ID_CANVAS,ScribbleWindow::onMouseDown),
FXMAPFUNC(SEL_LEFTBUTTONRELEASE,ScribbleWindow::ID_CANVAS,ScribbleWindow::onMouseUp),
FXMAPFUNC(SEL_MOTION, ScribbleWindow::ID_CANVAS,ScribbleWindow::onMouseMove),
FXMAPFUNC(SEL_COMMAND, ScribbleWindow::ID_CLEAR, ScribbleWindow::onCmdClear),
FXMAPFUNC(SEL_UPDATE, ScribbleWindow::ID_CLEAR, ScribbleWindow::onUpdClear),
};
</pre>
<p>
Note several things about this table; first, there are several messages
with the same <b><i>id</i></b>, but a different <b><i>type</i></b>. Message
types indicate what happened, for example, SEL_LEFTBUTTONPRESS means that
the left mouse button was just pressed. The message id identifies
the source. FOX defines a large collection of message types, each
of them has a specific meaning.
<p>Next, we need to implement the ``boilerplate'' stuff that the previous
FXDECLARE macro has declared:
<p>
<pre>
FXIMPLEMENT(ScribbleWindow,FXMainWindow,ScribbleWindowMap,ARRAYNUMBER(ScribbleWindowMap))
</pre>
<p>
This the first argument of the macro should have the name of the
class, in this case ScribbleWindow; the second argument should be the name
of the class from which the class has been derived; in this case, that's
FXMainWindow. The last to arguments are a pointer to the message
map, and the number of messages in that map. FOX has a convenience
macro ARRAYNUMBER() that expands to the number of elements in a compile-time
defined array; this makes it easier to add or remove messages.
<p>If the class you're defining implements no additional messages, the
last two arguments of FXIMPLEMENT should be simply NULL and 0.
<p>The remainder of the ScribbleWindow's implementation is pretty much
ordinary C++ code. The constructor follows below:
<p>
<pre>
// Construct a ScribbleWindow
ScribbleWindow::ScribbleWindow(FXApp *a):FXMainWindow(a,"ScribbleApplication",NULL,NULL,DECOR_ALL,0,0,800,600){
contents=new FXHorizontalFrame(this,LAYOUT_SIDE_TOP|LAYOUT_FILL_X|LAYOUT_FILL_Y,0,0,0,0,0,0,0,0);
// LEFT pane to contain the canvas
canvasFrame=new FXVerticalFrame(contents,
FRAME_SUNKEN|LAYOUT_FILL_X|LAYOUT_FILL_Y|LAYOUT_TOP|LAYOUT_LEFT,0,0,0,0,10,10,10,10);
// Label above the canvas
new FXLabel(canvasFrame,"CanvasFrame",NULL,JUSTIFY_CENTER_X|LAYOUT_FILL_X);
// Horizontal divider line
new FXHorizontalSeparator(canvasFrame,SEPARATOR_GROOVE|LAYOUT_FILL_X);
// Drawing canvas
canvas=new FXCanvas(canvasFrame,this,ID_CANVAS,
FRAME_SUNKEN|FRAME_THICK|LAYOUT_FILL_X|LAYOUT_FILL_Y|LAYOUT_TOP|LAYOUT_LEFT);
// RIGHT pane for the buttons
buttonFrame=new FXVerticalFrame(contents,
FRAME_SUNKEN|LAYOUT_FILL_Y|LAYOUT_TOP|LAYOUT_LEFT,0,0,0,0,10,10,10,10);
// Label above the buttons
new FXLabel(buttonFrame,"ButtonFrame",NULL,JUSTIFY_CENTER_X|LAYOUT_FILL_X);
// Horizontal divider line
new FXHorizontalSeparator(buttonFrame,SEPARATOR_RIDGE|LAYOUT_FILL_X);
// Button to clear
new FXButton(buttonFrame,"&Clear",NULL,this,ID_CLEAR,
FRAME_THICK|FRAME_RAISED|LAYOUT_FILL_X|LAYOUT_TOP|LAYOUT_LEFT,0,0,0,0,10,10,5,5);
// Exit button
new FXButton(buttonFrame,"&Exit",NULL,getApp(),FXApp::ID_QUIT,
FRAME_THICK|FRAME_RAISED|LAYOUT_FILL_X|LAYOUT_TOP|LAYOUT_LEFT,0,0,0,0,10,10,5,5);
// Initialize private variables
drawColor=FXRGB(255,0,0);
mdflag=0;
dirty=0;
}
</pre>
<p>
In almost all cases, it takes just one line of C++ code to create a FOX
Widget. Typically, that is a constructor invocation. As most
FOX Widget supply convenient default parameters to the constructor, you
may not have to specify most of them.
<p>The first line in the body of the constructor creates a top level window;
toplevel windows in FOX have no parent, so pass in a pointer to the application
object (<b><i>this</i></b> in this case). The remaining parameters
are the window title, window decorations (such as resize handles, borders,
etc.), as well as the initial size and position. The initial size
and position may be ignored by your particular window manager, they are
just hints.
<p>The next line creates a FXHorizontalFrame Widget. The FXHorizontalFrame
Widget is a <a href="layout.html#LAYOUT">Layout Manager</a> that places
its children horizontally.
<p>The FXMainWindow Widget itself is also a Layout Manager, and the options
passed to the FXHorizontalFrame widget's constructor determine how
it is placed in the FXMainWindow.
<p>Next, two FXVerticalFrame widgets are created, one for the drawing Canvas
and one for the buttons. In the canvasFrame, we then place a Label,
a grooved Separator, and the Canvas for drawing into. The Canvas's
target object is ScribbleWindow (i.e. <b><i>this</i></b>), and its message
is set to ID_CANVAS. This causes Canvas to send all its messages
to the ScribbleApp object, with the ID set to ID_CANVAS.
<p>Likewise, in the right buttonFrame we place a Label, a grooved Separator,
and two Buttons. The clear button has a caption "&Clear".
The & in front of a latter will cause the Button to install a hot-key
Alt-C automatically. The caption is drawn with the C underlines,
as in "<u>C</u>lear." The target of the clear Button is again the
ScribbleApp object, and its message ID is ID_CLEAR. Likewise, the
exit Button sends ID_QUIT.
<p>Note that we didn't have to define ID_QUIT, as this is a message every
FXApp object already understands. Thus, we can simply hook
up buttons to their targets.
<p>The remaining arguments to the Buttons determine its frame style (FRAME_THICK|FRAME_RAISED),
and how it is placed inside the VerticalFrame Layout Manager (LAYOUT_FILL_X|LAYOUT_TOP|LAYOUT_LEFT)
tells the Layout Manager to stretch the Buttons to fill the available room,
making them nicely the same size.
<p>Finally, the ScribbleWindow's constructor initializes its member variables
for the drawing color and the flags.
<p>Next, we implement the create() routine:
<p>
<pre>
// Create and initialize
void ScribbleWindow::create(){
// Create the windows
FXMainWindow::create();
// Make the main window appear
show();
}
</pre>
<p>
First, we call the base classes' create; then, the main window is shown
on the screen by calling its show() member function.
<p>Now, we're ready to handle some messages:
<p>
<pre>
// Mouse button was pressed somewhere
long ScribbleWindow::onMouseDown(FXObject*,FXSelector,void*){
// While the mouse is down, we'll draw lines
mdflag=1;
return 1;
}
// The mouse has moved, draw a line
long ScribbleWindow::onMouseMove(FXObject*, FXSelector,void* ptr){
FXEvent *ev=(FXEvent*)ptr;
if(mdflag){
// Get DC for the canvas
FXDCWindow dc(canvas);
// Set foreground color
dc.setForeground(drawColor);
// Draw line
dc.drawLine(ev->last_x, ev->last_y,ev->win_x, ev->win_y);
// We have drawn something, sonow the canvas is dirty
dirty=1;
}
return 1;
}
// The mouse button was released again
long ScribbleWindow::onMouseUp(FXObject*,FXSelector,void*ptr){
FXEvent *ev=(FXEvent*) ptr;
if(mdflag){
FXDCWindow dc(canvas);
dc.setForeground(drawColor);
dc.drawLine(ev->last_x, ev->last_y,ev->win_x, ev->win_y);
// We have drawn something, sonow the canvas is dirty
dirty=1;
// Mouse no longer down
mdflag=0;
}
return 1;
}
// Paint the canvas
long ScribbleWindow::onPaint(FXObject*,FXSelector,void*ptr){
FXEvent *ev=(FXEvent*)ptr;
FXDCWindow dc(canvas,ev);
dc.setForeground(canvas->getBackColor());
dc.fillRectangle(ev->rect.x,ev->rect.y,ev->rect.w,ev->rect.h);
return 1;
}
</pre>
<p>The <i>onMouseDown</i> message handler simply sets a flag to remember
than the mouse is now down; the <i>onMouseMove</i> handler draws
a line from the last to the current mouse positions; it then sets a dirty
flag to 1 to remember that the Canvas has been drawn onto. The <i>onMouseUp</i>
handler finishes the line, and resets the mouse down flag. Finally,
the <i>onPaint</i> handler repaints the canvas to the background color.
<br>Nothing remarkable here at all.
<p>The next few message handlers are more interesting:
<p>
<pre>
// Handle the clear message
long ScribbleWindow::onCmdClear(FXObject*,FXSelector,void*){
FXDCWindow dc(canvas);
dc.setForeground(canvas->getBackColor());
dc.fillRectangle(0,0,canvas->getWidth(),canvas->getHeight());
dirty=0;
return 1;
}
// Update the clear button
long ScribbleWindow::onUpdClear(FXObject* sender,FXSelector,void*){
if(dirty)
sender->handle(this,FXSEL(SEL_COMMAND,ID_ENABLE),NULL);
else
sender->handle(this,FXSEL(SEL_COMMAND,ID_DISABLE),NULL);
return 1;
}
</pre>
<p>
The <i>onCmdClear</i> message handler clears the canvas, then resets the
dirty flag. The <i>onUpdClear</i> message handler <b><i>updates</i></b>
the clear Button.
<p>Each Widget in FOX receives a message during idle processing asking
it to be updated. For example, Buttons can be sensitized or desensitized
when the state of the application changes. In this case, we desensitize
the sender (the clear Button) when the Canvas has already been cleared,
and sensitize it when it has been painted (as indicated by the dirty flag).
<p>This GUI Update process is extremely powerful:- if an application has
N commands, and M Widgets to update for each command, one might have to
write NxM update routines; with the GUI Update process, one needs to write
only N+M routines. Moreover, if the application data change by some
other means (e.g. timers, external data inputs, mulitple computing threads,
etc), the GUI will automatically keep itself up to date without any additional
coding.
<p>To complete the Scribble Application, only one thing remains:- to kick
it all off from the main() routine:
<p>
<pre>
// Here we begin
int main(int argc,char *argv[]){
// Make application
FXApp* application=new FXApp("Scribble","Test");
// Start app
application->init(argc,argv);
// Scribble window
new ScribbleWindow(application);
// Create the application's windows
application->create();
// Run the application
application->run();
return 0;
}
</pre>
<p>
First, we construct a FXApp object by calling<i> new FXApp("Scribble","Test").</i>
The first string is the name of the application `Scribble' is often referred
to as the Application Key, while the second string`Test' is called the
Vendor Key. Together, these two strings are used to determine the
application's registry- or preference-settings.
<p>The call to <i>application->init(argc,argv) </i>initializes the application;
argc and argv of the command line are passed in so that the FOX system
can filter out some FOX-specific command line arguments, such as for example
the <i>-display</i> parameter.
<p>The call <i>new ScribbleWindow(application)</i><tt><font size=-1> </font></tt>builds
the entire GUI for our application; the GUI consists essentially of two
parts:- the <i>client-side </i>resources, which live in our own process,
and the <i>server-side</i> resources which live in the X server (X11) or
GDI (Windows).
<br>When we construct a FOX widget, only the client-side resources are
determined. A subsequent call to <i>application->create()</i> recursively
creates all server-side resources for each widget that has been previously
constructed.
<p>Finally, <i>application->run()</i> member function is called to run
the application. This function never returns.
<br>
</ul>
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<p>
<table width=100% cellpadding=0 cellspacing=2><tr><td width=100% valign=bottom id=HEADLINE><b>
Recap
<br><img src='art/line.gif' width=100% height=1></b></td></tr></table>
<p>
<!--- TOPIC TITLE -->
<ul>
In the previous example, several FOX features have been discussed:
<br><br>
<ul>
<li>Building applications using FOX means <b><i>building</i></b> more C++ classes;
these new classes should always be derived from FXObject, either directly
or indirectly. The sophisticated developer will try and make these
new classes general, so that he/she may use these again in some other project.
Thus, the development effort may be leveraged many times over.<br>
</li>
<br><br>
<li>FOX uses a target/message system; Each message handler has three arguments:-
the sender of the message, which is always an object derived from FXObject,
the message selector, which is a combination of the message <b><i>type</i></b>
and message <b><i>id</i></b>, and a void pointer which may provide additional
information about the message. The message type identifies the type
of action that occurred, whereas the message id identifies the source of
the message; it makes the message unique.<br>
</li>
<br><br>
<li>When <b><i>defining</i></b> new messages, use <b><i>enums</i></b>.
The first new message for a derived class should be equal to the base classes
ID_LAST. This way, the compiler takes care of unique message numbering.
Note that messages should be <i><b>unique</b> </i>with respect to <i><b>a
specific target</b> </i>only:- unrelated targets do not have to be unique.
If the class you're writing may be subclassed later, define a message ID_LAST,
so that the subclass may define additional message id's starting from that
point.<br>
</li>
<br><br>
<li>Major FOX building blocks already understand a bunch of messages; for example,
FXApp understands the message ID_QUIT. This means that in many cases,
simple <b><i>glue-cod</i></b>e may be avoided.<br>
</li>
<br><br>
<li>During idle processing, FOX <b><i>automatically updates </i></b>eachWidget<b><i>,</i></b>
by asking the Widget's target what its state should be; the message being
sent to the target object is of type SEL_UPDATE. The GUI Update process
is an important tool to use for large-scale applications, where multiple
developers may not even be aware of which widgets may need updating when
some data structure changes. With GUI Updating, it is easy to keep
it consistent.<br>
</li>
<br><br>
<li>Hot Keys may be set on Button captions simply by prefixing the hotkey latter
with an <b><i>&</i></b>. The indicated letter will be automatically
underlined.<br>
</li>
<br><br>
<li>FOX uses a two-step process to build its Widgets; in the construction phase,
C++ data structures are built, and member data are filled in; in the second
phase, the connection to the display is established, and actual windows
are created for each Widget.</li>
</ul>
</ul>
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<img src='art/line.gif' width=100% height=1><font size=-1>
Copyright © 1997-2004 Jeroen van der Zijp</font>
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