Ramps in platform games

var y1;
//Roll back movement
//This is necessary as GM may or may not have carried out "Solid" behaviour
x=xprevious
y=yprevious
//Check if we're on the ground
if not (jump or place_free(x,y+1))
{
  jump=false  
  //We're on the ground so check we haven't just walked off a cliff
  y1=abs(round(x+hspeed)-round(x))
  if not place_free(x+hspeed,round(y)+y1+1)
  {
      //Search for the ground level
      x+=hspeed;
      y1+=(y1=0)
      y=round(y+y1)
      move_outside_solid(90,y1*2)  
      //Roughly set vspeed for the benefit of any AIs that may use it
      vspeed=(y-yprevious)
      //Check if we hit a wall.
      if not place_free(x,y)
      {
          x=xprevious
          y=yprevious
          if hspeed<>0
          {
            move_contact_solid(180*(hspeed<0),abs(hspeed))
          }  
          hspeed=0
          vspeed=0
      }
  }
  else
  {
    //Lookout!! Cliff!!
    // vspeed=0
    //Just move out horizontally
    move_contact_solid(180*(hspeed<0),abs(hspeed))
    jump=true
  }  
}
else
{
  //Freefall code
  //check for no collision at all
  if place_free(x+hspeed,y+vspeed)
  {
    x+=hspeed
    y+=vspeed
  }
  else
  {
    //collision so find out where
    //Move horizontally
    if hspeed<>0
    {
      move_contact_solid(180*(hspeed<0),abs(hspeed))
      if not (place_free(x+sign(hspeed),y) or place_free(x+sign(hspeed),y-2))
      {
        hspeed=0
      }
    }
    //Move vertically
    if vspeed<>0
    {
      move_contact_solid(90+180*(vspeed>0),abs(vspeed))
      if not place_free(x,y+sign(vspeed))
      {
        if vspeed>0
        {
          jump=false
        }
        vspeed=0
      }
    }
  }
}