It depends on how you use it.
I made a GameMaker example (GM8 attached):
Create event:
size1 = 5; //rectangles original size
size2 = 100; //rectangles target size
timer = 0; //time passed since increasing
s = 0; //rectangles size to be drawn
half_point = 15; //halfway point where speed is max, best to take half the fps
delay = 5; //to slow down the increase of the rectangle the higher the longer the it takes.
Draw Event:
//just some color settings unimportant
draw_set_color(c_blue);
draw_set_alpha(1);
//calculate the size that needs to be drawn of the rectangle
s = size1 + (size2-size1) / (1 + exp( -(timer / delay - half_point) ));
//draw rectangle
draw_rectangle(view_wview[0]/2-s,
view_hview[0]/2-s,
view_wview[0]/2+s,
view_hview[0]/2+s,
false);
//increase the time passed Game Maker necessity
timer += 1;
//reset when done increasing not really important
if(timer == 2*half_point*delay){
timer = 0;
//In order to also decrease just swap the sizes
var p;
p = size1;
size1 = size2;
size2 = p;
}
