Here is a code that I wrote which will allow you to zoom in and out with the mouse wheel, also you can hold down the middle mouse and move the camera around. It is set up for an RPG, so the camera is third person, the mouse mode will automatically change back and forth for you between camera functions, and selection cursor. The camera rotates around the player, you can play with the camera arc. and z position to move it higher or lower. Have fun!

Code:

---

function default_camera()
{
	camera.clip_near = 0;
	camera.tilt = -15;
//	distance_to_player = c_trace (camera.x, player.x, IGNORE_ME | IGNORE_SPRITES | IGNORE_PASSABLE);
	while (1)
	{ 
		if (mickey.z > 1)
		{
			mouse_mode = 0;
			camera.arc += 10 * time_step;
		}
		if (mickey.z < -1)
		{
			mouse_mode = 0;
			camera.arc -= 10 * time_step; // play with "10"
		}
		if(mouse_middle == 1)
		{
			mouse_mode = 0;
			key_a = 0;
			key_d = 0;
			camera.pan -= mouse_force.x * 5 * time_step; //turn left and right
			camera.tilt += mouse_force.y * 5 * time_step;
			camera.x = player.x - 200 * cos(camera.pan); // camera follows player
			camera.y = player.y - 200 * sin(camera.pan); // same here
			camera.z = player.z +200; // place the camera above the player
			vec_set(mouse_pos,mouse_cursor); // gets the point of cursor
		} 
		else
		{
			mouse_mode = 2;
			camera.x = player.x - 200 * cos(player.pan); // camera follows player
			camera.y = player.y - 200 * sin(player.pan); // same here
			camera.z = player.z +200; // place the camera above the player
			camera.pan = player.pan; // the camera and the player have the same pan angle
			vec_set(mouse_pos,mouse_cursor);
		}
 		camera.arc = minv (maxv (camera.arc, 10), 120);
 		wait (1);
 	}
}  

---

be sure to include this in your main function in this order:

Code:

---

mouse_mode = 0;
wait(3);
// now load the level
level_load("your_level.wmb");
while (player == NULL) {wait (1);}
mouse_map = yourmousemap_pcx;   
default_camera(); 

---