Update monitor struct to know if monintor edges are OUTSIDE_EDGE or INSIDE_EDGE

[somiaj]

• What is it which fvwm3 doesn't do at the moment, but should?

EdgeScroll doesn't fully function when using multiple monitors that have different sizes, because fvwm only detects when the mouse is at the edge of the outer most boundary (which may not be the monitor edge).

• How might fvwm3 need to change?

Fvwm needs to know if a monitor edge is an OUTSIDE_EDGE (there are no more monitors between that edge and outer most boundary) or an INSIDE_EDGE (this edge is partially shared with another monitor). This way EdgeScroll can check to see if a mouse is on an OUTSIDE_EDGE as opposed to the outer most boundary.

My thought is to add this info to the monitor struct, maybe to the screen_info sub struct. Something like

int monitor->screen_info->top,
    monitor->screen_info->bottom,
    monitor->screen_info->right,
    monitor->screen_info->left;

I think it is possible to determine if an edge is an INSIDE_EDGE by checking if the location of one monitor is at the far edge of another monitor.

m1->si->x == m2->si->x + m2->si->w || m1->si->y == m2->si->y + m2->si->h;

otherwise it is an OUTSIDE_EDGE.

(I also think this info could be used in DesktopConfiguration per-monintor or global to trigger EdgeScroll when on an INSIDE_EDGE as well).