/// <summary>
/// Tests to see if an object's intended x- and y-displacements are fully achievable in its
/// current room and position. Causes a collision and modifies the displacement value if
/// it would send the object into a collideable surface.
/// </summary>
/// <param name="obj">The object to be evaluated.</param>
/// <param name="room">The room in which the object is located and trying to move.</param>
/// <param name="time">The amount of time since the last frame.</param>
public static void Update(PhysicsObject obj, Room room, GameTime time)
{
PhysicsObject ridingAtStart = obj.riding;
float totalTime = (float)(time.ElapsedGameTime.TotalSeconds);
//All ungrounded, gravity-affected objects will have the displacement caused by
//gravity in this frame added to their y-displacement.
if (obj.IsGravityAffected && !obj.IsOnGround)
obj.DisplacementY = Math.Min(obj.DisplacementY + (GRAVITY / 2) * (totalTime * totalTime), MAX_FALLING_SPEED * totalTime);
obj.DisplacementX = (float)((int)(obj.DisplacementX));
obj.DisplacementY = (float)((int)(obj.DisplacementY));
//If the object will get stuck trying to move the originally intended amount, a collision
//has occurred. The appropriate velocity & acceleration variables as well as boolean flags
//will be reset, by calling the appropriate collision function (HitCeiling(), Land(), or
//HitWall()).
//Then the intended displacement is decreased by one until the object finds a coordinate
//at which it will no longer be stuck.
if (obj.DisplacementY < 0)
{
if (obj.IsStuck(room, 0, (int)obj.DisplacementY))
{
obj.HitCeiling();
obj.DisplacementY += 1;
while (obj.DisplacementY != 0 && obj.IsStuck(room, 0, (int)obj.DisplacementY))
obj.DisplacementY += 1;
}
if (obj.SticksToSurfaces && obj.DisplacementX == 0)
{
if (obj.WillLoseSurface(room))
{
while (obj.WillLoseSurface(room))
obj.DisplacementY += 1;
}
}
}
else if (obj.DisplacementY > 0)
{
if (obj.IsStuck(room, 0, (int)obj.DisplacementY))
{
obj.Land();
obj.DisplacementY -= 1;
while (obj.DisplacementY != 0 && obj.IsStuck(room, 0, (int)obj.DisplacementY))
obj.DisplacementY -= 1;
}
if (obj.SticksToSurfaces && obj.DisplacementX == 0)
{
if (obj.WillLoseSurface(room))
{
while (obj.WillLoseSurface(room))
obj.DisplacementY -= 1;
}
}
}
if (obj.DisplacementX > 0)
{
if (obj.IsStuck(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
{
obj.CollideRight();
obj.DisplacementX -= 1;
while (obj.DisplacementX != 0 && obj.IsStuck(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.DisplacementX -= 1;
}
if (!obj.MovesOffEdges && obj.IsOnGround && obj.DisplacementY == 0)
{
if (obj.WillMovePastEdge(room))
{
obj.VelocityX *= -1;
while (obj.WillMovePastEdge(room))
obj.DisplacementX -= 1;
}
}
if (obj.SticksToSurfaces && obj.DisplacementY == 0)
{
if (obj.WillLoseSurface(room))
{
while (obj.WillLoseSurface(room))
obj.DisplacementX -= 1;
}
}
}
else if (obj.DisplacementX < 0)
{
if (obj.IsStuck(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
{
obj.CollideLeft();
obj.DisplacementX += 1;
while (obj.DisplacementX != 0 && obj.IsStuck(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.DisplacementX += 1;
}
if (!obj.MovesOffEdges && obj.IsOnGround && obj.DisplacementY == 0)
{
if (obj.WillMovePastEdge(room))
{
obj.VelocityX *= -1;
while (obj.WillMovePastEdge(room))
obj.DisplacementX += 1;
}
}
if (obj.SticksToSurfaces && obj.DisplacementY == 0)
{
if (obj.WillLoseSurface(room))
{
while (obj.WillLoseSurface(room))
obj.DisplacementX += 1;
}
}
}
else if (obj.DisplacementX == 0 && obj.DisplacementY == 0)
{
if (obj.IsStuck(room, 0, 0))
{
if (obj.WallOnLeft && !obj.WallOnRight)
obj.DisplacementX += STUCK_OBJ_DISPLACEMENT;
else if (obj.WallOnRight && !obj.WallOnLeft)
obj.DisplacementX -= STUCK_OBJ_DISPLACEMENT;
}
}
//Even if a displacement value goes unchanged in the above test, it's still possible that the object
//will (not) have a wall beside or ground beneath them after moving their full displacements. This last
//test checks to see if this is the case, and changes the appropriate boolean flags accordingly.
//If the object is touching a floor in its new position, the appropriate collision-causing function
//is called.
//If an object was airborne at the beginning of the frame and is still airborne, its y-velocity
//is increased by the acceleration due to gravity.
//If it's determined that the object is now in the air, it will become airborne.
if (!obj.WallOnLeft)
{
if (obj.CheckWallLeft(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.CollideLeft();
}
else
{
if (!obj.CheckWallLeft(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.WallOnLeft = false;
}
if (!obj.WallOnRight)
{
if (obj.CheckWallRight(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.CollideRight();
}
else
{
if (!obj.CheckWallRight(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.WallOnRight = false;
}
if (!obj.IsOnGround)
{
if (obj.CheckGround(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.Land();
else if (obj.IsGravityAffected)
obj.VelocityY = Math.Min(obj.VelocityY + GRAVITY * totalTime, MAX_FALLING_SPEED);
}
else
{
if (!obj.CheckGround(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.LeaveGround();
}
if (!obj.CeilingAbove)
{
if (obj.CheckCeiling(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.HitCeiling();
}
else
{
if (!obj.CheckCeiling(room, (int)obj.DisplacementX, (int)obj.DisplacementY))
obj.LeaveCeiling();
}
if ((obj.riding != null) && (obj.riding == ridingAtStart))
{
obj.DisplacementX += ridingAtStart.DisplacementX;
obj.DisplacementY += ridingAtStart.DisplacementY;
}
}