scroll to the right or left if needed - actionscript-3

Question

I'm making a platform game.
My game level is very large and I'd like to make the gameLevel scroll when the player is walking.
So far it's scrolling, but the scrolling speed is not fast enough and when the player is walking to the right, he goes out of the screen.
Do you know how I can speed up the scrolling in order to prevent the character to exceed the middle of the screen ?
Here's my code for the scrolling screen :
// scroll to the right or left if needed
public function scrollWithHero() {
var stagePosition:Number = gamelevel.x+hero.mc.x;
var rightEdge:Number = 400-edgeDistance;
var leftEdge:Number = edgeDistance;
if (stagePosition > rightEdge) {
gamelevel.x -= (stagePosition-rightEdge);
if (gamelevel.x < -(gamelevel.width-stage.stageWidth)) gamelevel.x = -(gamelevel.width-stage.stageWidth);
}
if (stagePosition < leftEdge) {
gamelevel.x += (leftEdge-stagePosition);
if (gamelevel.x > 0) gamelevel.x = 0;
}
}

Answer 1

There are two ways you can scroll a screen.
The first would be to scroll at the exact same speed as the player's movement. which would mean that you do not really move the player, but rather scroll the world (the player would remain in the exact same place on-screen). This is not a very "elegant" way to go, but many games use it and it works.
The second (and better, IMHO) way would be to define some area around the center of the screen and allow the player to move around within this area. Only once the player reaches the end (to left/right) of this area do you start scrolling. This provides a much smoother effect.
So to implement the area, you need a size for it (lets say 100 as an example) and 300 is the center of the screen. So in this case your "area" would be from 250 to 350. Now you will need to detect when the player moves beyond this area and then scroll (instead of moving the player). This can be implemented as follows:
const CENTER:Number = 300; // center position on screen
const SIZE:Number = 100; // size of the movement area
const LEFT:Number = CENTER - (SIZE/2); // left of movement area
const RIGHT:Number = CENTER + (SIZE/2); // right of movement area
public function scrollWithHero() {
var scrollAmount:Number = 0; // holds amount to scroll by (init to none)
if ( hero.mc.x < LEFT ) { // if left of movement area reached
scrollAmount = LEFT - hero.mc.x; // calculate scroll amount
hero.mc.x = LEFT; // keep player at left of movement area
}
else if ( hero.mc.x > right ) { // else if right of movement area reached
scrollAmount = hero.mc.x - right; // calculate scroll amount
hero.mc.x = RIGHT; // keep player at right of movement area
}
// here you can use scrollAmount to scroll the level, and the player's
// position to calculate their offset into your level
}
This is a basic example just to calculate the relevant values, you will still need to use them, but this should illustrate the idea of how the scrolling works.
You should experiment with the size to find an area that feels good for your implementation. Also, if you set SIZE=0 then the player will remain in the center of the screen (i.e. it will work as described in the first implementation).