My target is to use QtCreator as IDE and compiler MinGW. Below I command (command line) to successfully compile the file sphere.cpp
Qt Code: 
  1. C:\Qt\progetti\FLTK\OpenGLSphere>g++ -I C:/MinGW/include -I C:/MinGW/include/FL/images -mwindows -DWIN32 -DUSE_OPENGL32 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -o 'sphere' 'sphere.cpp' -mwindows C:/MinGW/lib/libfltk_gl.a -lglu32 -lopengl32 C:/MinGW/lib/libfltk.a -lole32 -luuid -lcomctl32
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sphere.cpp:
Qt Code: 
  1. #include <FL/Fl.H>
  2. #include <FL/Fl_Window.H>
  3. #include <FL/glut.H>
  4. #include <FL/gl.h>
  5. #define WIDTH  640
  6. #define HEIGHT 480
  7. //
  8. // Render a simple opengl shaded sphere with a single side light -- erco 11/28/08        
  9. //
  10. //    1.1 Mods to use pure glut calls for subwindow -- erco 03/15/11
  11. //
  12. // You can build this example with: fltk-config --use-glut --compile sphere.cxx
  13. //
  14.  
  15. // GLUT: RESHAPE THE VIEWPORT
  16. void Reshape(int W, int H) {
  17.     // (REFERENCE: SGI light.c DEMO)
  18.     GLfloat ratio = (float)W / (float)H;
  19.     glViewport(0, 0, (GLsizei)W, (GLsizei)H);
  20.     glMatrixMode(GL_PROJECTION);
  21.     glLoadIdentity();
  22.     glOrtho(-1.5*ratio, 1.5*ratio, -1.5, 1.5, -10.0, 10.0);
  23.     glMatrixMode(GL_MODELVIEW);
  24.     glLoadIdentity();
  25. }
  26. // GLUT: REDRAW THE SCENE
  27. void Redraw() {
  28.     static int valid = 0;
  29.     if (!valid) {
  30.         valid = 1;
  31.         Reshape(WIDTH, HEIGHT);
  32.         // (REFERENCE: SGI 'light.c' EXAMPLE)
  33.         GLfloat mat_ambient[]    = { 1.0, 1.0, 1.0, 1.0 };  // RGBA
  34.         GLfloat mat_diffuse[]    = { 1.0, 1.0, 1.0, 1.0 };  // RGBA
  35.         GLfloat mat_specular[]   = { 1.0, 1.0, 1.0, 1.0 };  // RGBA
  36.         GLfloat light_position[] = { 5.0, 5.0, 0.0, 0.0 };  // XYZ
  37.         glClearColor(0.0, 0.0, 0.4, 0.0);                   // bg color
  38.         glShadeModel(GL_SMOOTH);
  39.         //
  40.         glMaterialfv(GL_FRONT, GL_AMBIENT,   mat_ambient);
  41.         glMaterialfv(GL_FRONT, GL_DIFFUSE,   mat_diffuse);
  42.         glMaterialfv(GL_FRONT, GL_SPECULAR,  mat_specular);
  43.         glMaterialf(GL_FRONT,  GL_SHININESS, 20.0);
  44.         glLightfv(GL_LIGHT0, GL_POSITION, light_position);
  45.         //
  46.         glEnable(GL_LIGHTING);
  47.         glEnable(GL_LIGHT0);
  48.         glEnable(GL_DEPTH_TEST);
  49.     }
  50.     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  51.     glPushMatrix();
  52.         glColor3f(0.5, 0.5, 0.5);
  53.         glutSolidSphere(0.5, 30, 30);
  54.     glPopMatrix();
  55. }
  56. int main(int argc, char *argv[]) {
  57.   Fl_Window win(WIDTH, HEIGHT, "sphere");
  58.   win.resizable(win);
  59.   win.show(argc, argv);
  60.   // Docs say to add glut subwindow /after/ calling win.show()
  61.   win.begin();
  62.     // glutInit(&argc, argv);   // docs say not to call this if a subwindow
  63.     glutInitWindowSize(WIDTH-20, HEIGHT-20);
  64.     glutInitWindowPosition(10,10); // place inside parent window
  65.     glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_MULTISAMPLE);
  66.     glutCreateWindow("sphere");
  67.     glutReshapeFunc(Reshape);
  68.     glutDisplayFunc(Redraw);
  69.   win.end();
  70.   return(Fl::run());
  71. }
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In the file sphere.pro as I set to get a successful compilation ?