One mouse click is registered twice C++ / GLUT

Question

I have to make some transformation with left mouse click. This is part of my code:

void mouse(int button, int state, int x, int y) {
if(button == GLUT_LEFT_BUTTON && v*p + xk <= 34 && v*p + yk <= 34 && v*p - xk <= 34 && v*p - yk <= 34) {
    std::cout << "Resized" << std::endl;
    p += 0.02;

    }
    glutPostRedisplay();
}

But when I do click once on the screen, it prints "Resized" twice. What could be the issue here?

Answer 1

The glutMouseFunc() is invoked once, when the mouse is pressed and once when the mouse is released.
When the mouse is pressed, then the actual state argument is GLUT_DOWN. When the mouse is released then the argument is GLUT_UP.

Additionally test if state == GLUT_DOWN:

void mouse(int button, int state, int x, int y) {

    if (state == GLUT_DOWN &&                      // <----
        button == GLUT_LEFT_BUTTON &&
        v*p + xk <= 34 && v*p + yk <= 34 && v*p - xk <= 34 && v*p - yk <= 34) {

        std::cout << "Resized" << std::endl;
        p += 0.02;
    }
    glutPostRedisplay();
}