What you have to do is implement it yourself using the Form's MouseMove and MouseDown events. This is a little more complicated if you have menus because then you also have to handle the menu's MouseMove and MouseDown as well because it will override the Form's events. The basics are:
private void panel1_MouseMove(object sender, MouseEventArgs e)
{
if ((e.X <= 2 && e.Y <= 2) || (e.X + 2 >= this.Width && e.Y + 2 >= this.Height))
{
this.Cursor = Cursors.SizeNWSE;
}
else if ((e.X + 2 >= this.Width && e.Y <= 2) || (e.X <= 2 && e.Y + 2 >= this.Height))
{
this.Cursor = Cursors.SizeNESW;
}
else if (e.X <= 2 || e.X + 2 >= this.Width)
{
this.Cursor = Cursors.SizeWE;
}
else if (e.Y <= 2 || e.Y + 2 >= this.Height)
{
this.Cursor = Cursors.SizeNS;
}
else
{
this.Cursor = Cursors.Default;
}
}
Of course, to fully implement it, you would have to check if the mouse was down (you can use a bool for that and set it in the MouseDown and MouseUp events) and then check to see which way it is being dragged. If it's being dragged up or left, you'd have to first move the form and then resize based on how much it moved. If it's to the right or bottom, you can just set the height and width to the mouse location (of course, check first, because it looks like the mouse isn't registered as being in the form until it is two less than the height and width).
And you could simplify it by only allowing them to resize using the bottom-right and you could add a picture in that corner indicating you can resize it.
[Update]
Actually, it's not going to be as simple as that. You would first have to do a global hook on the mouse. The reason is that MouseMove won't work when you move outside of the form, which you would have to do to resize it. So, it can be done, but again, you'd have to use a global hook. An article on how to do that is here:
Processing Global Mouse and Keyboard Hooks in C#[
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