/** \page opengl Using OpenGL This chapter discusses using FLTK for your OpenGL applications. \section opengl_using Using OpenGL in FLTK The easiest way to make an OpenGL display is to subclass Fl_Gl_Window. Your subclass must implement a \p draw() method which uses OpenGL calls to draw the display. Your main program should call \p redraw() when the display needs to change, and (somewhat later) FLTK will call \p draw(). With a bit of care you can also use OpenGL to draw into normal FLTK windows. This allows you to use Gouraud shading for drawing your widgets. To do this you use the \ref opengl_gl_start "gl_start()" and \ref opengl_gl_finish "gl_finish()" functions around your OpenGL code. gl_start() and gl_finish() functions around your OpenGL code. You must include FLTK's \p header file. It will include the file \p , define some extra drawing functions provided by FLTK, and include the \p header file needed by WIN32 applications. \section opengl_subclass Making a Subclass of Fl_Gl_Window To make a subclass of Fl_Gl_Window, you must provide: \li A class definition. \li A \p draw() method. \li A \p handle() method if you need to receive input from the user. If your subclass provides static controls in the window, they must be redrawn whenever the \p FL_DAMAGE_ALL bit is set in the value returned by \p damage(). For double-buffered windows you will need to surround the drawing code with the following code to make sure that both buffers are redrawn: \code #ifndef MESA glDrawBuffer(GL_FRONT_AND_BACK); #endif // !MESA ... draw stuff here ... #ifndef MESA glDrawBuffer(GL_BACK); #endif // !MESA \endcode
Note: If you are using the Mesa graphics library, the call to \p glDrawBuffer() is not required and will slow down drawing considerably. The preprocessor instructions shown above will optimize your code based upon the graphics library used.
\subsection opengl_defining Defining the Subclass To define the subclass you just subclass the Fl_Gl_Window class: \code 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) {} }; \endcode The \p draw() and \p handle() methods are described below. Like any widget, you can include additional private and public data in your class (such as scene graph information, etc.) \subsection opengl_draw The draw() Method The \p draw() method is where you actually do your OpenGL drawing: \code 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 ... } \endcode \subsection opengl_handle The handle() Method The \p handle() method handles mouse and keyboard events for the window: \code 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; case FL_SHORTCUT: ... shortcut, key is in Fl::event_key(), ascii in Fl::event_text() ... Return 1 if you understand/use the shortcut event, 0 otherwise... return 1; default: // pass other events to the base class... return Fl_Gl_Window::handle(event); } } \endcode When \p handle() is called, the OpenGL context is not set up! If your display changes, you should call \p redraw() and let \p draw() do the work. Don't call any OpenGL drawing functions from inside \p handle()! You can call \e some OpenGL stuff like hit detection and texture loading functions by doing: \code 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... \endcode Your main program can now create one of your windows by doing new MyWindow(...). You can also use your new window class in FLUID by: -# Putting your class definition in a \p MyWindow.H file. -# Creating a Fl_Box widget in FLUID. -# In the widget panel fill in the "class" field with \p MyWindow. This will make FLUID produce constructors for your new class. -# In the "Extra Code" field put \#include "MyWindow.H", so that the FLUID output file will compile. You must put glwindow->show() in your main code after calling \p show() on the window containing the OpenGL window. \section opengl_normal Using OpenGL in Normal FLTK Windows You can put OpenGL code into the \p draw() method, as described in \ref subclassing_drawing in the previous chapter, or into the code for a \ref common_boxtypes "boxtype" or other places with some care. Fl_Widget::draw() method or into the code for a boxtype or other places with some care. Most importantly, before you show \e any 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 \p Fl_Gl_Window::mode() to describe how you intend to use OpenGL: \code Fl::gl_visual(FL_RGB); \endcode You can then put OpenGL drawing code anywhere you can draw normally by surrounding it with: \code gl_start(); ... put your OpenGL code here ... gl_finish(); \endcode \anchor opengl_gl_start \anchor opengl_gl_finish \p gl_start() and \p gl_finish() 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 \p glScissor() commands. These functions also synchronize the OpenGL graphics stream with the drawing done by other X, WIN32, or FLTK functions. The same context is reused each time. If your code changes the projection transformation or anything else you should use \p glPushMatrix() and \p glPopMatrix() functions to put the state back before calling \p gl_finish(). You may want to use Fl_Window::current()->h() to get the drawable height so that you can flip the Y coordinates. Unfortunately, there are a bunch of limitations you must adhere to for maximum portability: \li You must choose a default visual with Fl::gl_visual(). \li You cannot pass \p FL_DOUBLE to Fl::gl_visual(). \li You cannot use Fl_Double_Window or Fl_Overlay_Window. Do \e not call \p gl_start() or \p gl_finish() when drawing into an Fl_Gl_Window ! \section opengl_drawing OpenGL Drawing Functions FLTK provides some useful OpenGL drawing functions. They can be freely mixed with any OpenGL calls, and are defined by including \p which you should include instead of the OpenGL header \p . void gl_color(Fl_Color) \par Sets the current OpenGL color to a FLTK color. For color-index modes it will use \p fl_xpixel(c), which is only right if this window uses the default colormap! void gl_rect(int x, int y, int w, int h)
void gl_rectf(int x, int y, int w, int h) \par Outlines or fills a rectangle with the current color. If Fl_Gl_Window::ortho() has been called, then the rectangle will exactly fill the pixel rectangle passed. void gl_font(Fl_Font fontid, int size) \par Sets the current OpenGL font to the same font you get by calling fl_font(). int gl_height()
int gl_descent()
float gl_width(const char *)
float gl_width(const char *, int n)
float gl_width(uchar) \par Returns information about the current OpenGL font. void gl_draw(const char *)
void gl_draw(const char *, int n) \par Draws a nul-terminated string or an array of \p n< characters in the current OpenGL font at the current raster position. void gl_draw(const char *, int x, int y)
void gl_draw(const char *, int n, int x, int y)
void gl_draw(const char *, float x, float y)
void gl_draw(const char *, int n, float x, float y) \par Draws a nul-terminated string or an array of \p n characters in the current OpenGL font at the given position. void gl_draw(const char *, int x, int y, int w, int h, Fl_Align) \par Draws 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 fl_draw(). \section opengl_speed Speeding up OpenGL Performance of Fl_Gl_Window may be improved on some types of OpenGL implementations, in particular MESA and other software emulators, by setting the \p GL_SWAP_TYPE environment variable. This variable declares what is in the backbuffer after you do a swapbuffers. \li setenv GL_SWAP_TYPE COPY

This indicates that the back buffer is copied to the front buffer, and still contains it's old data. This is true of many hardware implementations. Setting this will speed up emulation of overlays, and widgets that can do partial update can take advantage of this as \p damage() will not be cleared to -1. \li setenv GL_SWAP_TYPE NODAMAGE

This indicates that nothing changes the back buffer except drawing into it. This is true of MESA and Win32 software emulation and perhaps some hardware emulation on systems with lots of memory. \li All other values for \p GL_SWAP_TYPE, and not setting the variable, cause FLTK to assume that the back buffer must be completely redrawn after a swap. This is easily tested by running the \p gl_overlay demo program and seeing if the display is correct when you drag another window over it or if you drag the window off the screen and back on. You have to exit and run the program again for it to see any changes to the environment variable. \section opengl_optimizer Using OpenGL Optimizer with FLTK OpenGL Optimizer is a scene graph toolkit for OpenGL available from Silicon Graphics for IRIX and Microsoft Windows. It allows you to view large scenes without writing a lot of OpenGL code. \par OptimizerWindow Class Definition \par To use OpenGL Optimizer with FLTK you'll need to create a subclass of Fl_Gl_Widget that includes several state variables: \code 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(); } } }; \endcode \par The camera() Method \par The \p camera() method sets the camera (projection and viewpoint) to use when drawing the scene. The scene is redrawn after this call. \par The draw() Method \par The \p draw() method performs the needed initialization and does the actual drawing: \code void OptimizerWindow::draw() { if (!context_) { // This is the first time we've been asked to draw; create the // Optimizer context for the scene... #ifdef WIN32 context_ = new csContext((HDC)fl_getHDC()); context_->ref(); context_->makeCurrent((HDC)fl_getHDC()); #else context_ = new csContext(fl_display, fl_visual); context_->ref(); context_->makeCurrent(fl_display, fl_window); #endif // WIN32 ... 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_); } } else { #ifdef WIN32 context_->makeCurrent((HDC)fl_getHDC()); #else context_->makeCurrent(fl_display, fl_window); #endif // WIN32 } 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_); } \endcode \par The scene() Method \par The \p >scene() method sets the scene to be drawn. The scene is a collection of 3D objects in a \p csGroup. The scene is redrawn after this call. \htmlonly
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