How would you detect a ground like this:

Question

I have made racing games in the past, but never a side scrolling type.
Im trying to make one similar to this: http://www.gamesfreak.net/games/Cyclo-Maniacs_3730.html
But how would you keep the player on the ground? well not stuck to the ground because we would want the player to be able to use things like ramps.
Would it be a hit test? hmmmmmmmm Any ideas? anyone.

Answer 1

Oh i apoligize. I pressumed because of the popularity of box2D you meant that. Well the code I have so far does a OK job for physics. Allthough i made it in intensions of a platform/side scroller. But its ok. I guess it could possibly be  modified for a car or something.
Here is what i have so far:
package
          import flash.display.MovieClip;
          import flash.events.Event;
          import flash.events.MouseEvent;
          import flash.events.KeyboardEvent;
          import flash.geom.Point;
          public class DocumentMain extends MovieClip
                    public var _startMarker:StartMarker = new StartMarker;
                    public var _Player:Player;
                    public var _Boundaries:Boundaries;
                    public var _Wall:Wall;
                    public var _Floor:Floor;
                    public var _LButton:LButton = new LButton;
                    public var _RButton:RButton = new RButton;
                    public var _UButton:UButton = new UButton;
                    public var _DButton:DButton = new DButton;
                    private var _vy:Number;
                    private var _vx:Number;
                    public function DocumentMain()
                              stage.focus = stage;
                              //stage.addChild(_startMarker);
                              //_startMarker.x = 300;
                              //_startMarker.y = 300;
                              stage.addChild(_LButton);
                              _LButton.x = 80;
                              _LButton.y = 600;
                              _LButton.height = 75;
                              _LButton.width = 75;
                              _LButton.addEventListener(MouseEvent.MOUSE_DOWN, LMouseDown);
                              _LButton.addEventListener(MouseEvent.MOUSE_UP, LMouseUp);
                              stage.addChild(_RButton);
                              _RButton.x = 210;
                              _RButton.y = 600;
                              _RButton.height = 75;
                              _RButton.width = 75;
                              _RButton.addEventListener(MouseEvent.MOUSE_DOWN, RMouseDown);
                              _RButton.addEventListener(MouseEvent.MOUSE_UP, RMouseUp);
                              stage.addChild(_DButton);
                              _DButton.x = 140;
                              _DButton.y = 650;
                              _DButton.height = 75;
                              _DButton.width = 75;
                              //_DButton.addEventListener(MouseEvent.MOUSE_DOWN, DMouseDown);
                              //_DButton.addEventListener(MouseEvent.MOUSE_UP, DMouseUp);
                              stage.addChild(_UButton);
                              _UButton.x = 140;
                              _UButton.y = 550;
                              _UButton.height = 75;
                              _UButton.width = 75;
                              _UButton.addEventListener(MouseEvent.MOUSE_DOWN, UpMouseDown);
                              _UButton.addEventListener(MouseEvent.MOUSE_UP, UpMouseUp);
                              _startMarker.visible = true;
                              _startMarker.x = 500;
                              _startMarker.y = 300;
                              _vx = 0;
                              _vy = 0;
                              _Player.addEventListener(MouseEvent.MOUSE_DOWN, JumpDownHandler);
                              _Player.addEventListener(MouseEvent.MOUSE_UP, JumpUpHandler);
                              this.addEventListener(Event.ENTER_FRAME, enterFrameHandler);
                              stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
                              stage.addEventListener(KeyboardEvent.KEY_UP, keyUpHandler);
                    private function JumpDownHandler(MouseEvent):void
                              _vy = -20;
                    private function JumpUpHandler(MouseEvent):void
                              _vy = 0;
                    private function LMouseDown(MouseEvent):void
                              _vx = -20;
                    private function LMouseUp(MouseEvent):void
                              trace("LMouseUp");
                              _vx = 0;
                    private function RMouseUp(MouseEvent):void
                              _vx = 0;
                    private function RMouseDown(MouseEvent):void
                              trace("RMouseDown");
                              _vx = 20;
                    private function UpMouseDown(MouseEvent):void
                              _vy = -20;
                    private function UpMouseUp(MouseEvent):void
                              trace("UMouseUp");
                              //_vx = 0;
                    private function enterFrameHandler(e:Event):void
                              _vy +=  2;
                              //_vx += 20;
                              _Player.x += + _vx;
                              _Player.y += + _vy;
                              processAllTheCollisions();
                              scrollTheStage();
                    private function processAllTheCollisions():void
                              if (_vy > 0)
                                        if (_Player.y > 500)
                                                  _Player.x = _startMarker.x;
                                                  _Player.y = _startMarker.y;
                                                  _Boundaries.x = 0;
                                                  _Boundaries.y = 0;
                                                  _vy = 0;
                                        else
                                                  var collision:Boolean = false;
                                                  if (_Boundaries.hitTestPoint(_Player.x,_Player.y,true))
                                                            collision = true;
                                                  if (collision)
                                                            while (collision)
                                                                      _Player.y -=  0.1;
                                                                      collision = false;
                                                                      if (_Boundaries.hitTestPoint(_Player.x, _Player.y, true))
                                                                                collision = true;
                                                            _vy = 0;
                    private function scrollTheStage():void
                              _Boundaries.x += (stage.stageWidth * 0.5) - _Player.x;
                              _Player.x = stage.stageWidth * 0.5;
                              //_Boundaries.y += (stage.stage.stageHeight * 0.5) - _Player.y;
                              //_Player.y = stage.stageHeight * 0.5;
                    private function keyDownHandler(e:KeyboardEvent):void
                              switch (e.keyCode)
                                        case 37 :
                                        _vx = -20;
                                        break;
                                        case 38 :
                                        _vy = -20;
                                        break;
                                        case 39:
                                        _vx = 20;
                                        break;
                                        default:
                    private function keyUpHandler(e:KeyboardEvent):void
                              switch (e.keyCode)
                                        case 37 :
                                        case 39 :
                                        _vx = 0;
                                        break;
                                        default: