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git-svn-id: file:///fltk/svn/fltk/branches/branch-1.0@1248 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
376 lines
14 KiB
HTML
376 lines
14 KiB
HTML
<HTML><BODY>
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<H1 ALIGN=RIGHT><A NAME=opengl>9 - Using OpenGL</A></H1>
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This chapter discusses using FLTK for your OpenGL applications.
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<H2>Using OpenGL in FLTK</H2>
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The easiest way to make an OpenGL display is to subclass <A href=Fl_Gl_Window.html#Fl_Gl_Window>
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<TT>Fl_Gl_Window</TT></A>. Your subclass must implement a <TT>draw()</TT>
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method which uses OpenGL calls to draw the display. Your main program
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should call <TT>redraw()</TT> when the display needs to change, and
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(somewhat later) FLTK will call <TT>draw()</TT>.
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<P>With a bit of care you can also use OpenGL to draw into normal FLTK
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windows. This allows you to use Gouraud shading for
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drawing your widgets. To do this you use the <A href=#gl_start><TT>
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gl_start()</TT></A> and <A href=#gl_finish><TT>gl_finish()</TT></A>
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functions around your OpenGL code. </P>
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<P>You must include FLTK's <TT><FL/gl.h></TT> header file. It will
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include the file <TT><GL/gl.h></TT>, define some extra drawing
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functions provided by FLTK, and include the <TT><windows.h></TT> header
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file needed by WIN32 applications. </P>
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<H2>Making a Subclass of Fl_Gl_Window</H2>
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To make a subclass of Fl_Gl_Window, you must provide:
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<UL>
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<LI>A class definition. </LI>
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<LI>A <TT>draw()</TT> method. </LI>
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<LI>A <TT>handle()</TT> method (if you need to recieve input from the
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user). </LI>
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</UL>
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If your subclass provides static controls in the window, they must be
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redrawn whenever the <tt>FL_DAMAGE_ALL</tt> bit is set in the value
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returned by <tt>damage()</tt>. For double-buffered windows you will
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need to surround the drawing code with the following code to make sure
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that both buffers are redrawn:
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<ul><pre>
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#ifndef MESA
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glDrawBuffer(GL_FRONT_AND_BACK);
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#endif // !MESA
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... draw stuff here ...
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#ifndef MESA
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glDrawBuffer(GL_BACK);
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#endif // !MESA
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</pre></ul>
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<B>Note:</B> If you are using the Mesa graphics library, the call to
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<tt>glDrawBuffer()</tt> is not required and will slow down drawing
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considerably. The preprocessor instructions shown above will optimize
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your code based upon the graphics library used.
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<H3>Defining the Subclass</H3>
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To define the subclass you just subclass the <TT>Fl_Gl_Window</TT> class:
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<UL>
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<PRE>
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class MyWindow : public Fl_Gl_Window {
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void draw();
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int handle(int);
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public:
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MyWindow(int X, int Y, int W, int H, const char *L)
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: Fl_Gl_Window(X, Y, W, H, L) {}
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};
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</PRE>
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</UL>
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The <TT>draw()</TT> and <TT>handle()</TT> methods are described below.
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Like any widget, you can include additional private and public data in
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your class (such as scene graph information, etc.)
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<H3>The draw() Method</H3>
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The <TT>draw()</TT> method is where you actually do your OpenGL
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drawing:
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<UL>
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<PRE>
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void MyWindow::draw() {
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if (!valid()) {
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... set up projection, viewport, etc ...
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... window size is in w() and h().
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... valid() is turned on by FLTK after draw() returns
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}
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... draw ...
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}
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</PRE>
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</UL>
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<H3>The handle() Method</H3>
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The <TT>handle()</TT> method handles mouse and keyboard events for the
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window:
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<UL>
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<PRE>
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int MyWindow::handle(int event) {
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switch(event) {
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case FL_PUSH:
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... mouse down event ...
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... position in Fl::event_x() and Fl::event_y()
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return 1;
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case FL_DRAG:
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... mouse moved while down event ...
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return 1;
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case FL_RELEASE:
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... mouse up event ...
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return 1;
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case FL_FOCUS :
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case FL_UNFOCUS :
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... Return 1 if you want keyboard events, 0 otherwise
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return 1;
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case FL_KEYBOARD:
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... keypress, key is in Fl::event_key(), ascii in Fl::event_text()
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... Return 1 if you understand/use the keyboard event, 0 otherwise...
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return 1;
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case FL_SHORTCUT:
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... shortcut, key is in Fl::event_key(), ascii in Fl::event_text()
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... Return 1 if you understand/use the shortcut event, 0 otherwise...
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return 1;
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default:
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// pass other events to the base class...
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return Fl_Gl_Window::handle(event);
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}
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}
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</PRE>
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</UL>
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When <TT>handle()</TT> is called, the OpenGL context is not set up!
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If your display changes, you should call <TT>redraw()</TT> and let <TT>
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draw()</TT> do the work. Don't call any OpenGL drawing functions from
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inside <TT>handle()</TT>!
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<P>You can call <I>some</I> OpenGL stuff like hit detection and texture
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loading functions by doing: </P>
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<UL>
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<PRE>
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case FL_PUSH:
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make_current(); // make OpenGL context current
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if (!valid()) {
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... set up projection exactly the same as draw ...
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valid(1); // stop it from doing this next time
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}
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... ok to call NON-DRAWING OpenGL code here, such as hit
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detection, loading textures, etc...
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</PRE>
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</UL>
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Your main program can now create one of your windows by doing <TT>new
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MyWindow(...)</TT>. You can also use <A href=FLUID.html#FLUID>FLUID</A>
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by:
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<OL>
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<LI>Putting your class definition in a <tt>MyWindow.H</tt> file. </LI>
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<LI>Creating a <tt>Fl_Box</tt> widget in FLUID.</LI>
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<LI>In the widget panel fill in the "class" field with <tt>MyWindow</tt>.
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This will make FLUID produce constructors for your new class. </LI>
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<LI>In the "Extra Code" field put <TT>#include "MyWindow.H"</TT>, so that
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the FLUID output file will compile. </LI>
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</OL>
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You must put <TT>glwindow->show()</TT> in your main code after calling <TT>
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show()</TT> on the window containing the OpenGL window.
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<H2>Using OpenGL in Normal FLTK Windows</H2>
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You can put OpenGL code into an <A href=#draw><TT>Fl_Widget::draw()</TT>
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</A> method or into the code for a <A href=common.html#boxtypes>boxtype</A>
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or other places with some care.
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<P>Most importantly, before you show <I>any</I> windows (including those
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that don't have OpenGL drawing) you <B>must</B> initialize FLTK so that it
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knows it is going to use OpenGL. You may use any of the symbols
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described for <A href=Fl_Gl_Window.html#Fl_Gl_Window.mode><TT>
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Fl_Gl_Window::mode()</TT></A> to describe how you intend to use OpenGL: </P>
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<UL>
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<PRE>
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Fl::gl_visual(FL_RGB);
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</PRE>
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</UL>
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You can then put OpenGL drawing code anywhere you can draw normally by
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surrounding it with:
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<UL>
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<PRE>
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gl_start();
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... put your OpenGL code here ...
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gl_finish();
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</PRE>
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</UL>
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<A name=gl_start><TT>gl_start()</TT></A> and <A name=gl_finish><TT>
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gl_finish()</TT></A> set up an OpenGL context with an orthographic
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projection so that 0,0 is the lower-left corner of the window and each
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pixel is one unit. The current clipping is reproduced with OpenGL <TT>
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glScissor()</TT> commands. These also synchronize the OpenGL graphics
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stream with the drawing done by other X, WIN32, or FLTK functions.
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<P>The same context is reused each time. If your code changes the
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projection transformation or anything else you should use <TT>
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glPushMatrix()</TT> and <TT>glPopMatrix()</TT> functions to put the
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state back before calling <TT>gl_finish()</TT>. </P>
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<P>You may want to use <TT>Fl_Window::current()->h()</TT> to get the
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drawable height so that you can flip the Y coordinates. </P>
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<P>Unfortunately, there are a bunch of limitations you must adhere to
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for maximum portability: </P>
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<UL>
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<LI>You must choose a default visual with <A href=functions.html#gl_visual>
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<TT>Fl::gl_visual()</TT></A>. </LI>
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<LI>You cannot pass <TT>FL_DOUBLE</TT> to <TT>Fl::gl_visual()</TT>.</LI>
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<LI>You cannot use <TT>Fl_Double_Window</TT> or <TT>Fl_Overlay_Window</TT>.</LI>
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</UL>
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Do <I>not</I> call <TT>gl_start()</TT> or <TT>gl_finish()</TT> when
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drawing into an <TT>Fl_Gl_Window</TT>!
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<H2>OpenGL Drawing Functions</H2>
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FLTK provides some useful OpenGL drawing functions. They can be
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freely mixed with any OpenGL calls, and are defined by including <TT>
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<FL/gl.H></TT> (which you should include instead of the OpenGL header <TT>
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<GL/gl.h></TT>).
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<H4>void gl_color(Fl_Color)</H4>
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Set the current color to a FLTK color. <I>For color-index modes
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it will use <TT>fl_xpixel(c)</TT>, which is only right if this window
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uses the default colormap!</I>
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<H4>void gl_rect(int x, int y, int w, int h)
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<BR> void gl_rectf(int x, int y, int w, int h)</H4>
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Outline or fill a rectangle with the current color. If
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<A HREF="Fl_Gl_Window.html#Fl_Gl_Window.ortho"><TT>Fl_Gl_Window::ortho()</TT></A>
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has been called, then the rectangle will exactly fill the pixel
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rectangle passed.
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<H4>void gl_font(Fl_Font fontid, int size)</H4>
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Set the current OpenGL font to the same font you get by calling <A href=drawing.html#fl_font>
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<TT>fl_font()</TT></A>.
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<H4>int gl_height()
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<BR> int gl_descent()
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<BR> float gl_width(const char *)
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<BR> float gl_width(const char *, int n)
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<BR> float gl_width(uchar)</H4>
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Return information about the current OpenGL font.
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<H4>void gl_draw(const char *)
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<BR> void gl_draw(const char *, int n)</H4>
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Draw a nul-terminated string or an array of <TT>n</TT> characters in
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the current OpenGL font at the current raster position.
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<H4>void gl_draw(const char *, int x, int y)
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<BR> void gl_draw(const char *, int n, int x, int y)
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<BR> void gl_draw(const char *, float x, float y)
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<BR> void gl_draw(const char *, int n, float x, float y)</H4>
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Draw a nul-terminated string or an array of <TT>n</TT> characters in
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the current OpenGL font at the given position.
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<H4>void gl_draw(const char *, int x, int y, int w, int h, Fl_Align)</H4>
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Draw a string formatted into a box, with newlines and tabs expanded,
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other control characters changed to ^X, and aligned with the edges or
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center. Exactly the same output as <A href=#fl_draw><TT>fl_draw()</TT></A>
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.
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<h2>Speeding up OpenGL</h2>
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Performance of Fl_Gl_Window may be improved on some types of OpenGL
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implementations (in particular MESA or other software emulators) by
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setting the <tt>GL_SWAP_TYPE</tt> environment variable. This variable
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declares what is in the back buffer after you do a swapbuffers.
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<ul>
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<li><tt>setenv GL_SWAP_TYPE COPY</tt>
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<p>This indicates that the back buffer is copied to the front buffer,
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and still contains it's old data. This is true of many hardware
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implementations. Setting this will speed up emulation of
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overlays, and widgets that can do partial update can take
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advantage of this as damage() will not be cleared to -1.
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<p>
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<li><tt>setenv GL_SWAP_TYPE NODAMAGE</tt>
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<p>This indicates that nothing changes the back buffer except drawing
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into it. This is true of MESA and Win32 software emulation and
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perhaps some hardware emulation on systems with lots of memory.
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<p>
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<li>All other values for <tt>GL_SWAP_TYPE</tt>, and not setting the variable,
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cause fltk to assumme that the back buffer must be completely
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redrawn after a swap.
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</ul>
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<p>This is easily tested by running the gl_overlay demo program and
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seeing if the display is correct when you drag another window over
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it or if you drag the window off the screen and back on. You have to
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exit and run the program again for it to see any changes to the
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environment variable.
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<H2>Using OpenGL Optimizer with FLTK</H2>
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<A href=http://www.sgi.com/software/optimizer>OpenGL Optimizer</A> is a
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scene graph toolkit for OpenGL available from Silicon Graphics for IRIX
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and Microsoft Windows. Versions are in the works for Solaris and
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HP-UX. It allows you to view large scenes without writing a lot of
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OpenGL code.
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<H4>OptimizerWindow Class Definition</H4>
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To use OpenGL Optimizer with FLTK you'll need to create a subclass of <TT>
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Fl_Gl_Widget</TT> that includes several state variables:
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<UL>
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<PRE>
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class OptimizerWindow : public Fl_Gl_Window {
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csContext *context_; // Initialized to 0 and set by draw()...
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csDrawAction *draw_action_; // Draw action...
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csGroup *scene_; // Scene to draw...
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csCamara *camera_; // Viewport for scene...
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void draw();
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public:
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OptimizerWindow(int X, int Y, int W, int H, const char *L)
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: Fl_Gl_Window(X, Y, W, H, L) {
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context_ = (csContext *)0;
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draw_action_ = (csDrawAction *)0;
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scene_ = (csGroup *)0;
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camera_ = (csCamera *)0;
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}
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void scene(csGroup *g) { scene_ = g; redraw(); }
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void camera(csCamera *c) {
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camera_ = c;
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if (context_) {
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draw_action_->setCamera(camera_);
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camera_->draw(draw_action_);
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redraw();
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}
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}
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};
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</PRE>
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</UL>
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<PRE>
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</PRE>
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<H4>The camera() Method</H4>
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The <TT>camera()</TT> method sets the camera (projection and
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viewpoint) to use when drawing the scene. The scene is redrawn after
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this call.
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<H4>The draw() Method</H4>
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The <TT>draw()</TT> method performs the needed initialization and does
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the actual drawing:
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<UL>
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<PRE>
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void OptimizerWindow::draw() {
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if (!context_) {
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// This is the first time we've been asked to draw; create the
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// Optimizer context for the scene...
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#ifdef WIN32
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context_ = new csContext((HDC)fl_getHDC());
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context_->ref();
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context_->makeCurrent((HDC)fl_getHDC());
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#else
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context_ = new csContext(fl_display, fl_visual);
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context_->ref();
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context_->makeCurrent(fl_display, fl_window);
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#endif // WIN32
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... perform other context setup as desired ...
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// Then create the draw action to handle drawing things...
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draw_action_ = new csDrawAction;
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if (camera_) {
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draw_action_->setCamera(camera_);
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camera_->draw(draw_action_);
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}
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} else {
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#ifdef WIN32
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context_->makeCurrent((HDC)fl_getHDC());
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#else
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context_->makeCurrent(fl_display, fl_window);
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#endif // WIN32
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}
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if (!valid()) {
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// Update the viewport for this context...
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context_->setViewport(0, 0, w(), h());
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}
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// Clear the window...
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context_->clear(csContext::COLOR_CLEAR | csContext::DEPTH_CLEAR,
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0.0f, // Red
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0.0f, // Green
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0.0f, // Blue
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1.0f); // Alpha
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// Then draw the scene (if any)...
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if (scene_)
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draw_action_->apply(scene_);
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}
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</PRE>
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</UL>
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<H4>The scene() Method</H4>
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The <TT>scene()</TT> method sets the scene to be drawn. The scene is
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a collection of 3D objects in a <TT>csGroup</TT>. The scene is redrawn
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after this call. </BODY></HTML>
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