1. OpenGL in FLTK

2. Timers Not 100% accurate (don't measure time with them)
Single shot timeouts
 void add_timeout(double t, Fl_Timeout_Handler, void* d)
call a function in t seconds
void remove_timeout(Fl_Timeout_Handler, void* d)
cancels a timeout (harmless if timer already triggered)
void repeat_timeout(double t, Fl_Timeout_Handler, void* d)
call a function t seconds after the last timeout triggered
can only be called from within a timer callback

3. Simple Timer Print "TICK" every second void callback(void*) {
    printf("PUTS");
    Fl::repeat_timeout(1.0, callback); }
int main()
    Fl::add_timeout(1.0, callback);
    return Fl::run()

4. Add Timer to Move Out CustomWidget
Goal: Have slider slide back and forth
Use globals for all variables and widgets
Make customWidget global
Add variable to control direction
Callback
Setup repeat timer
Move widget in specified direction
Check if we have reached max or min and change direction
Main
Set initial direction
Initial timer call

5. Idle Similar to GLUT add_idle(void (*cb)(void*), void *)
function to call whenever nothing else is happening
can have multiple callbacks
remove_timout(void (*cb)(void*), void *)
removes callback function if it exists

6. OpenGL Widget Create a subclass of Fl_Gl_Window
#include <FL/Fl_Gl_Window.H>
#include <FL/gl.h>
Will include <GL/gl.h>
Need to implement draw function in subclass
Setup view port
valid() will return false if needed
Actual drawing

7. OpenGL Widget
class OpenGLWindow : public Fl_Gl_Window { private:     void draw() {
        if ( !valid() ) {
             // initialization
        }
        // draw
    }; public:     OpenGLWindow(int x, int y, int w, int h,
                 const char* l = 0)
        : Fl_Gl_Window(x, y, w, h, l) { }; };

8. 3D Gasket in FLTK Put all code into subclass of Fl_Gl_Window
Copy triangle, tetra, and divide_tetra functions
Move colors into tetra and v into draw
All reference to width are height need to be replaced with w() and h()
Hard code number of sub divisions
Create a window and place OpenGL widget in it

9. Widget to Control Sub Divisions
Recommendation: make all widgets global
OpenGL draw() now get value from slider widget
divide_tetra(v[0], v[1], v[2], v[3],
             divisions->value());
Add a slider (and label) for number of sub divisions
    divisions = new Fl_Slider(100, 480, 540,
                              20);     divisions->type(FL_HORIZONTAL);     divisions->range(1, 20);     divisions->step(1);

10. Widget to Control Sub Divisions
Need to tell FLTK/OpenGL Widget to update
call widget's redraw()
Need to redraw when we change slider (callback)
 void update(Fl_Widget*, void*) {     glwindow->redraw(); }
    // when creating slider
    divisions->callback(update);

11. Assignment 1 Part 3 in FLTK
Will use toggle button instead of mouse clicks
Timer instead of idle
Create toggle button and start timer
spinning = new Fl_Button(545, 485, 90, 20,
                         "Spinning");
spinning->type(FL_TOGGLE_BUTTON);
Fl::add_timeout(1, timer, 0);
spin = 0.0f;

12. Assignment 1 Part 3 in FLTK
Update spin and redraw if necessary
void timer(void*) {     Fl::repeat_timeout(0.02, timer);     if ( spinning->value() )     {         spin += 1.0f;         if ( spin > 360.0f )             spin -= 360.0f;         glwindow->redraw();     } }  

13. Assignment 1 Part 3 in FLTK
Add spin to OpenGL widget
extern float spin;
Rotate before drawing (before glBegin)
glLoadIdentity();
glRotatef(spin, 0.0f, 1.0f, 0.0f);

14. Events Implement int handle(int event)
event is mouse click & drag, mouse wheel, keyboard presses & release, system events
Return 1 if event use
Event consumed
Return 0 is unesed
Event will continue to be passed around
Additional helper functions
Mouse: event_button() event_x() 
Keyboard: event_key()

15. Spin Triangle with Mouse
Goal: mouse drags will rotate object
Filter out only used event
Pass rest to default handler
No previous mouse position with drag event (only current)
Initial click will seed last position
Need to hold current state

16. Spin Triangle with Mouse
Header:
    int oldX, oldY;
    float vRotation, hRotation;
    int handle(int event);
Constructor:
    vRotation = hRotation = 0.0f;
Draw:
    glRotatef(hRotation, 0.0f, 1.0f, 0.0f);
    glRotatef(vRotation, 1.0f, 0.0f, 0.0f);

17. Spin Triangle with Mouse
Handle
switch ( event ) {
case FL_DRAG: 
    hRotation += Fl::event_x() - oldX; 
    vRotation += Fl::event_y() - oldY; 
    redraw(); 
case FL_PUSH: 
    oldX = Fl::event_x(); 
    oldY = Fl::event_y(); 
    return 1; 
default: return Fl_Gl_Window::handle(event);  }