glutSetWindow man page
glutSetWindow — Select the <i>current window</i>
OpenGLUT - window
All OpenGL rendering goes to the
. Many OpenGLUT functions also implicitly use the
Many OpenGLUT callback operations are tied to a window. When your callback is invoked, OpenGLUT will set that particular window to be the
. However, some callbacks---such as that registered via glutIdleFunc()---do not have associated windows. If a callback is not associated to a particular window, then when OpenGLUT invokes that callback you should
use glutSetWindow() to select the appropriate window before doing any OpenGL rendering or doing any OpenGLUT window-related operations.
There may be cases when you can get away with assuming that the
is unchanged since some prior time, but OpenGLUT has considerable liberaty with respect to when it invokes your functions. Also, your program may add more windows or more operations on other windows as you develop it.
Lastly, this is a convenient way to select among multiple windows for drawing without actually waiting for that window's display callback. Simply set the
and draw immediately. This is not always advisable, but may be practical.
It is an error to set the
to a non-existant window (e.g., one that you have closed). A warning will be printed on
if you try to do so, and the
should be unchanged.