Mouse Callback Function

I wonder if there is any mouse function (opengl) which when you double click on an item in your window or a specific area or in a subwindow to display a message box…?

OpenGL doesn’t have any input functions of any kind. You have to look at whatever windowing API you’re using to do such things.

if I put
void mymouse(int btn, int state, int x, int y)
if(btn==GLUT_LEFT_BUTTON && state==…) code
by which methods can I display a messagebox contain 4-5 of informations after --> if(btn==GLUT_LEFT_BUTTON && state==…)

That is also provided by your windowing API. GLUT, however, does not provide it, so you have to do it some other way. On Windows, check out MessageBox.

You can also use printf if you just need to dump some debug information. On Windows, your project needs be a console based application, which is probably the case since you are using GLUT.