d7b88a3bcc
Revision 1. git-svn-id: file:///fltk/svn/fltk/trunk@219 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
302 lines
11 KiB
HTML
302 lines
11 KiB
HTML
<HTML><BODY>
|
|
<H1 ALIGN=RIGHT><A NAME=opengl>9 - Using OpenGL</A></H1>
|
|
This chapter discusses using FLTK for your OpenGL applications.
|
|
<H2>Using OpenGL in FLTK</H2>
|
|
The easiest way to make an OpenGL display is to subclass <A href=Fl_Gl_Window.html#Fl_Gl_Window>
|
|
<TT>Fl_Gl_Window</TT></A>. Your subclass must implement a <TT>draw()</TT>
|
|
method which uses OpenGL calls to draw the display. Your main program
|
|
should call <TT>redraw()</TT> when the display needs to change, and
|
|
(somewhat later) FLTK will call <TT>draw()</TT>.
|
|
<P>With a bit of care you can also use OpenGL to draw into normal FLTK
|
|
windows. This is mostly useful because you can use Gourand shading for
|
|
drawing your widgets. To do this you use the <A href=#gl_start><TT>
|
|
gl_start()</TT></A> and <A href=#gl_finish><TT>gl_finish()</TT></A>
|
|
functions around your OpenGL code. </P>
|
|
<P>You must include FLTK's <TT><FL/gl.h></TT> header file. It will
|
|
include the file <TT><GL/gl.h></TT>, define some extra drawing
|
|
functions provided by FLTK, and include the <TT><windows.h></TT> header
|
|
file needed by WIN32 applications. </P>
|
|
<H2>Making a Subclass of Fl_Gl_Window</H2>
|
|
To make a subclass of Fl_Gl_Window, you must provide:
|
|
<UL>
|
|
<LI>A class definition. </LI>
|
|
<LI>A <TT>draw()</TT> method. </LI>
|
|
<LI>A <TT>handle()</TT> method (if you need to recieve input from the
|
|
user). </LI>
|
|
</UL>
|
|
<H3>Defining the Subclass</H3>
|
|
To define the subclass you just subclass <TT>Fl_Gl_Window</TT> class:
|
|
<UL>
|
|
<PRE>
|
|
class MyWindow : public Fl_Gl_Window {
|
|
void draw();
|
|
int handle(int);
|
|
|
|
public:
|
|
MyWindow(int X, int Y, int W, int H, const char *L)
|
|
: Fl_Gl_Window(X, Y, W, H, L) {}
|
|
};
|
|
</PRE>
|
|
</UL>
|
|
The <TT>draw()</TT> and <TT>handle()</TT> methods are described below.
|
|
Like any widget, you can include additional private and public data in
|
|
your class (such as scene graph information, etc.)
|
|
<H3>The draw() Method</H3>
|
|
The <TT>draw()</TT> method is where you actually do your OpenGL
|
|
drawing:
|
|
<UL>
|
|
<PRE>
|
|
void MyWindow::draw() {
|
|
if (!valid()) {
|
|
... set up projection, viewport, etc ...
|
|
... window size is in w() and h().
|
|
... valid() is turned on by FLTK after draw() returns
|
|
}
|
|
... draw ...
|
|
}
|
|
</PRE>
|
|
</UL>
|
|
<H3>The handle() Method</H3>
|
|
The <TT>handle()</TT> method handles mouse and keyboard events for the
|
|
window:
|
|
<UL>
|
|
<PRE>
|
|
int MyWindow::handle(int event) {
|
|
switch(event) {
|
|
case FL_PUSH:
|
|
... mouse down event ...
|
|
... position in Fl::event_x() and Fl::event_y()
|
|
return 1;
|
|
case FL_DRAG:
|
|
... mouse moved while down event ...
|
|
return 1;
|
|
case FL_RELEASE:
|
|
... mouse up event ...
|
|
return 1;
|
|
case FL_FOCUS :
|
|
case FL_UNFOCUS :
|
|
... Return 1 if you want keyboard events, 0 otherwise
|
|
return 1;
|
|
case FL_KEYBOARD:
|
|
... keypress, key is in Fl::event_key(), ascii in Fl::event_text()
|
|
... Return 1 if you understand/use the keyboard event, 0 otherwise...
|
|
return 1;
|
|
default:
|
|
// tell FLTK that I don't understand other events
|
|
return 0;
|
|
}
|
|
}
|
|
</PRE>
|
|
</UL>
|
|
When <TT>handle()</TT> is called, the OpenGL context is not set up!
|
|
If your display changes, you should call <TT>redraw()</TT> and let <TT>
|
|
draw()</TT> do the work. Don't call any OpenGL drawing functions from
|
|
inside <TT>handle()</TT>!
|
|
<P>You can call some OpenGL stuff like hit detection and texture
|
|
loading functions by doing: </P>
|
|
<UL>
|
|
<PRE>
|
|
case FL_PUSH:
|
|
make_current(); // make OpenGL context current
|
|
if (!valid()) {
|
|
... set up projection exactly the same as draw ...
|
|
valid(1); // stop it from doing this next time
|
|
}
|
|
... ok to call NON-DRAWING OpenGL code here, such as hit
|
|
detection, loading textures, etc...
|
|
</PRE>
|
|
</UL>
|
|
Your main program can now create one of your windows by doing <TT>new
|
|
MyWindow(...)</TT>. You can also use <A href=fluid.html#fluid>fluid</A>
|
|
by:
|
|
<OL>
|
|
<LI>Put your class definition in a MyWindow.H file. </LI>
|
|
<LI>In fluid create a box object, resize place where you want. </LI>
|
|
<LI>In the control panel, fill in the "class" field with MyWindow.H.
|
|
This will make fluid produce constructors for your new class. </LI>
|
|
<LI>In the "extra code" put <TT>#include "MyWindow.H"</TT>, so that
|
|
the fluid output file will compile. </LI>
|
|
</OL>
|
|
You must put <TT>glwindow->show()</TT> in your main code after calling <TT>
|
|
show()</TT> on the window containing the OpenGL window.
|
|
<H2>Using OpenGL in Normal FLTK Windows</H2>
|
|
You can put OpenGL code into an <A href=#draw><TT>Fl_Widget::draw()</TT>
|
|
</A> method or into the code for a <A href=common.html#boxtypes>boxtype</A>
|
|
or other places with some care.
|
|
<P>Most important, before you show <I>any</I> windows (including those
|
|
that don't have OpenGL drawing) you must initialize FLTK so that it
|
|
knows it is going to use OpenGL. You may use any of the symbols
|
|
described for <A href=Fl_Gl_Window.html#Fl_Gl_Window.mode><TT>
|
|
Fl_Gl_Window::mode()</TT></A> to describe how you intend to use OpenGL: </P>
|
|
<UL>
|
|
<PRE>
|
|
Fl::gl_visual(FL_RGB);
|
|
</PRE>
|
|
</UL>
|
|
You can then put OpenGL drawing code anywhere you can draw normally by
|
|
surrounding it with:
|
|
<UL>
|
|
<PRE>
|
|
gl_start();
|
|
... put your OpenGL code here ...
|
|
gl_finish();
|
|
</PRE>
|
|
</UL>
|
|
<A name=gl_start><TT>gl_start()</TT></A> and <A name=gl_finish><TT>
|
|
gl_finish()</TT></A> set up an OpenGL context with an orthographic
|
|
projection so that 0,0 is the lower-left corner of the window and each
|
|
pixel is one unit. The current clipping is reproduced with OpenGL <TT>
|
|
glScissor()</TT> commands. These also synchronize the OpenGL graphics
|
|
stream with the drawing done by other X, WIN32, or FLTK functions.
|
|
<P>The same context is reused each time. If your code changes the
|
|
projection transformation or anything else you should use <TT>
|
|
glPushMatrix()</TT> and <TT>glPopMatrix()</TT> functions to put the
|
|
state back before calling <TT>gl_finish()</TT>. </P>
|
|
<P>You may want to use <TT>Fl_Window::current()->h()</TT> to get the
|
|
drawable height so you can flip the Y coordinates. </P>
|
|
<P>Unfortunately, there are a bunch of limitations you must adhere to
|
|
for maximum portability: </P>
|
|
<UL>
|
|
<LI>You must choose a default visual with <A href=functions.html#gl_visual>
|
|
<TT>Fl::gl_visual()</TT></A>. </LI>
|
|
<LI>You cannot pass <TT>FL_DOUBLE</TT> to <TT>Fl::gl_visual()</TT>. </LI>
|
|
<LI>You cannot use <TT>Fl_Double_Window</TT> or <TT>Fl_Overlay_Window</TT>
|
|
. </LI>
|
|
</UL>
|
|
Do <I>not</I> call <TT>gl_start()</TT> or <TT>gl_finish()</TT> when
|
|
drawing into an <TT>Fl_Gl_Window</TT>!
|
|
<H2>OpenGL drawing functions</H2>
|
|
FLTK provides some useful OpenGL drawing functions. They can be
|
|
freely mixed with any OpenGL calls, and are defined by including <TT>
|
|
<FL/gl.H></TT> (which you should include instead of the OpenGL header <TT>
|
|
<GL/gl.h></TT>).
|
|
<H3>void gl_color(Fl_Color)</H3>
|
|
Set the current color to a FLTK color index. <I>For color-index modes
|
|
it will use <TT>fl_xpixel(c)</TT>, which is only right if this window
|
|
uses the default colormap!</I>
|
|
<H3>void gl_rect(int x, int y, int w, int h)
|
|
<BR> void gl_rectf(int x, int y, int w, int h)</H3>
|
|
Outline or fill a rectangle with the current color. If <TT>ortho()</TT>
|
|
has been called, then the rectangle will exactly fill the pixel
|
|
rectangle passed.
|
|
<H3>void gl_font(Fl_Font fontid, int size)</H3>
|
|
Set the "current OpenGL font" to the same font you get by calling <A href=drawing.html#fl_font>
|
|
<TT>fl_font()</TT></A>.
|
|
<H3>int gl_height()
|
|
<BR> int gl_descent()
|
|
<BR> float gl_width(const char *)
|
|
<BR> float gl_width(const char *, int n)
|
|
<BR> float gl_width(uchar)</H3>
|
|
Return information about the current OpenGL font.
|
|
<H3>void gl_draw(const char *)
|
|
<BR> void gl_draw(const char *, int n)</H3>
|
|
Draw a nul-terminated string or an array of <TT>n</TT> characters in
|
|
the current OpenGL font at the current <TT>glRasterPos</TT>.
|
|
<H3>void gl_draw(const char *, int x, int y)
|
|
<BR> void gl_draw(const char *, int n, int x, int y)
|
|
<BR> void gl_draw(const char *, float x, float y)
|
|
<BR> void gl_draw(const char *, int n, float x, float y)</H3>
|
|
Draw a nul-terminated string or an array of <TT>n</TT> characters in
|
|
the current OpenGL font at the given position.
|
|
<H3>void gl_draw(const char *, int x, int y, int w, int h, Fl_Align)</H3>
|
|
Draw a string formatted into a box, with newlines and tabs expanded,
|
|
other control characters changed to ^X, and aligned with the edges or
|
|
center. Exactly the same output as <A href=#fl_draw><TT>fl_draw()</TT></A>
|
|
.
|
|
<H2>Using OpenGL Optimizer with FLTK</H2>
|
|
<A href=http://www.sgi.com/software/optimizer>OpenGL Optimizer</A> is a
|
|
scene graph toolkit for OpenGL available from Silicon Graphics for IRIX
|
|
and Microsoft Windows. Versions are in the works for Solaris and
|
|
HP-UX. It allows you to view large scenes without writing a lot of
|
|
OpenGL code.
|
|
<H3>OptimizerWindow Class Definition</H3>
|
|
To use OpenGL Optimizer with FLTK you'll need to create a subclass of <TT>
|
|
Fl_Gl_Widget</TT> that includes several state variables:
|
|
<UL>
|
|
<PRE>
|
|
class OptimizerWindow : public Fl_Gl_Window {
|
|
csContext *context_; // Initialized to 0 and set by draw()...
|
|
csDrawAction *draw_action_; // Draw action...
|
|
csGroup *scene_; // Scene to draw...
|
|
csCamara *camera_; // Viewport for scene...
|
|
|
|
void draw();
|
|
|
|
public:
|
|
OptimizerWindow(int X, int Y, int W, int H, const char *L)
|
|
: Fl_Gl_Window(X, Y, W, H, L) {
|
|
context_ = (csContext *)0;
|
|
draw_action_ = (csDrawAction *)0;
|
|
scene_ = (csGroup *)0;
|
|
camera_ = (csCamera *)0;
|
|
}
|
|
|
|
void scene(csGroup *g) { scene_ = g; redraw(); }
|
|
|
|
void camera(csCamera *c) {
|
|
camera_ = c;
|
|
if (context_) {
|
|
draw_action_->setCamera(camera_);
|
|
camera_->draw(draw_action_);
|
|
redraw();
|
|
}
|
|
}
|
|
};
|
|
</PRE>
|
|
</UL>
|
|
<PRE>
|
|
|
|
</PRE>
|
|
<H3>The camera() Method</H3>
|
|
The <TT>camera()</TT> method sets the camera (projection and
|
|
viewpoint) to use when drawing the scene. The scene is redrawn after
|
|
this call.
|
|
<H3>The draw() Method</H3>
|
|
The <TT>draw()</TT> method performs the needed initialization and does
|
|
the actual drawing:
|
|
<UL>
|
|
<PRE>
|
|
void OptimizerWindow::draw() {
|
|
if (!context_) {
|
|
// This is the first time we've been asked to draw; create the
|
|
// Optimizer context for the scene...
|
|
|
|
context_ = new csContext(fl_display, fl_visual);
|
|
context_->ref();
|
|
context_->makeCurrent(fl_display, fl_window);
|
|
|
|
... perform other context setup as desired ...
|
|
|
|
// Then create the draw action to handle drawing things...
|
|
|
|
draw_action_ = new csDrawAction;
|
|
if (camera_) {
|
|
draw_action_->setCamera(camera_);
|
|
camera_->draw(draw_action_);
|
|
}
|
|
}
|
|
|
|
if (!valid()) {
|
|
// Update the viewport for this context...
|
|
context_->setViewport(0, 0, w(), h());
|
|
}
|
|
|
|
// Clear the window...
|
|
|
|
context_->clear(csContext::COLOR_CLEAR | csContext::DEPTH_CLEAR,
|
|
0.0f, // Red
|
|
0.0f, // Green
|
|
0.0f, // Blue
|
|
1.0f); // Alpha
|
|
|
|
// Then draw the scene (if any)...
|
|
|
|
if (scene_)
|
|
draw_action_->apply(scene_);
|
|
}
|
|
</PRE>
|
|
</UL>
|
|
<H3>The scene() Method</H3>
|
|
The <TT>scene()</TT> method sets the scene to be drawn. The scene is
|
|
a collection of 3D objects in a <TT>csGroup</TT>. The scene is redrawn
|
|
after this call. </BODY></HTML> |