Programming and Graphics

254 Introduction to C++ Programming and Graphics

glutCreateWindow("GLUT window");

glClearColor(0.8,0.5,0.2,1.0);

glutDisplayFunc(blank);

glutMainLoop();

return 0;

}

//-- function blank

void blank()

{

glClear(GLCOLORBUFFERBIT);

}

The code makes severalGlut(glut) and OpenGL (gl) calls according to a very
specific protocol:

• The first command in the main program calls theGlutfunction:

glutInit(int &argc, char **argv);

This function parses the window-specific parameters transmitted to the

X11 server. Note that the first argument is the integer pointer, &argc.

• The last command in the main program calls the function:

glutMainLoop();

which launches the graphics display in an infinite loop that can be inter-

rupted only by certain events.

In OpenGL and GLUT programming, we first register the callbacks (graph-

ics functions), then define the graphics object, and finally launch the

graphics display by entering the main loop.If we do not enter the main

loop, nothing will happen.

• The second command in the main program generates a graphics window
  and defines the title.


• The third command in the main program sets the background color painted
  when the window is cleared in the default RBGA mode.


• The fourth command in the main program calls the function:

glutDisplayFunc(char functionname);

This function launches the user-defined function stated in the argument.