set_mouse_range()
Do you mean that?

Check if it's outside your arbitrary bounds, and if it is, move it back with position_mouse()

He said position_mouse() and I quote

But I'm guessing he's calling it a little bit too much.

[edit]

Click attachments when you write a post...
Or copy and paste your code inside some

<code>tags</code>

[/edit]

Maybe get_mouse_mickeys is going to be best for your situation... I'll wait for you to post your code first though.

Hmm... to check if the mouse is inside your circle you should use... the equation of a cirlce! (otherwise known as pythagoras<- did i spell that right?)

X^2 + Y^2 = r^2

where x and y are the mouse's co-ords, and r is the radius of your circle, if they are greater than the result is greater than r^2, then the mouse is outside of your circle.

And each loop through your logic, if the mouse is inside the circle, store its co-ords in some int's, when its outside the circle, set the mouse position to the last know co-ords of the mouse.

That should be one quick way of keeping your mouse in a circle

Now, you'll also need to offset the x and y co-ords of the mouse when you check them, since the origin of the circle would be the top left of the screen.

As for a curved area, make a bigger circle, and adjust the offsets. If you have no idea what i've been rambling on about, say so.

Yes manually draw the sprite.

This might be a bad way, but it could work...

Before the game begins, make a 2d integer array. Set its width and height to the maximum distance you want the mouse to be able to travel.

int max_distance = 200;    // Radius of the circle
int mouse_box[400][400];
int xd;
int yd;

for (int i = 0; i < 400; ++i) {
        for (int j = 0; j < 400; ++j) {

                xd = i - max_distance;
                yd = j - max_distance;
                // Check Distance
                mouse_box<i>[j] = (sqrt(xd * xd + yd * yd) < max_distance);
        }
}

I didn't test it, but that should create an array with the shape of a circle in "1's" and outside the circle in "0's"

Now all you have to do is record where the mouse was in the previous game cycle, and check its current position against the array.

If it works, it should work fast.

Yeah you could do a distance check every time but that would be slow, hence my happy binary circle. I didn't know position_mouse() was so slow. That's stupid. Allegro's stupid. Life sucks.

EDIT:
To the OP:
What if you made the cursor disappear? Then you could just not draw it, and not process any clicks or movement. I don't know what kind of game you're making though.

Thats pretty clever peelemachine, like what i said, but you only need to do the math once.