glutDisplayFunc

glutDisplayFunc is a function in the OpenGL Utility Toolkit (GLUT) used to register the display callback for the current window. The display callback is called by GLUT whenever the window needs to be redrawn, such as after creation, when it is exposed, or when a redraw is requested programmatically.

Prototype and behavior: void glutDisplayFunc(void (*func)(void)); The argument is a pointer to a function that takes no parameters and returns void. The display callback should render the scene using OpenGL commands. After rendering, you typically present the frame by either swapping the front and back buffers (glutSwapBuffers) if the window uses double buffering, or by flushing the command stream (glFlush) for single buffering.

Usage: After creating a window with glutCreateWindow and configuring the display mode with glutInitDisplayMode, assign the callback by calling glutDisplayFunc with your display function, for example glutDisplayFunc(display); Then enter the GLUT event loop with glutMainLoop(). If you have multiple windows, set the display callback for each window; the callback is associated with the currently focused window, so you may need to switch windows with glutSetWindow when necessary. You can request a redraw at any time by calling glutPostRedisplay, which marks the window for redrawing and triggers the display callback at the next opportunity.

Example (plain text):

void display(void) {

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// drawing commands here

glutSwapBuffers(); // if using GLUT_DOUBLE

}

int main(int argc, char** argv) {

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

glutInitWindowSize(640, 480);

glutCreateWindow("Example");

glutDisplayFunc(display);

glutMainLoop();

return 0;

}

Notes: The display callback is central to rendering in GLUT and is invoked in response to internal events as part of the GLUT event loop.