no, screen_size is the engine resolution. it doesn't change if you resize the window but the rendered image gets distorted. this isn't wanted in most cases.

so in the event i would like to get the space that is available for the directx surface like that:

Code:
void resize_event(sizex, sizey) // the same for maximize event
{
    // adapt engine resolution to the available space
    video_set(sizex, sizey, 0, 0);
}