8 directional movement - Maintain vertical position

Question

I have a top-down game that has 8 directions of movement (top/down/left/right/topright/topleft/bottomright/bottomleft). There are sprites for each direction of movement. This is just an example spritesheet:

The problem is when I want to retain the vertical position. When I let go of the buttons on the keyboard, it polls the keys quickly and ends up facing the character in either left/right/up/down position depending on the last key that was released.

I added a delay for polling the keypresses, but I do not like this solution as it creates a noticeable lag.

Can anyone think of logic that would be able to allow my sprite to retain the proper direction when the keys are unpressed? Here is the current code:

if (kbState.IsKeyDown(Keys.Up) && kbState.IsKeyDown(Keys.Left))
    character.ChangeDirection(Direction.UpLeft);
else if (kbState.IsKeyDown(Keys.Up) && kbState.IsKeyDown(Keys.Right))
    character.ChangeDirection(Direction.UpRight);
else if (kbState.IsKeyDown(Keys.Down) && kbState.IsKeyDown(Keys.Left))
    character.ChangeDirection(Direction.DownLeft);
else if (kbState.IsKeyDown(Keys.Down) && kbState.IsKeyDown(Keys.Right))
    character.ChangeDirection(Direction.DownRight);
else  if (kbState.IsKeyDown(Keys.Up))
    character.ChangeDirection(Direction.Up);
else if (kbState.IsKeyDown(Keys.Down))
    character.ChangeDirection(Direction.Down);
else if (kbState.IsKeyDown(Keys.Left))
    character.ChangeDirection(Direction.Left);
else if (kbState.IsKeyDown(Keys.Right))
    character.ChangeDirection(Direction.Right);

---

Edit

Settled for the following code:

float delay = 0.04f;
float DELAY = 0.04f;
....

//Get movement 
delay -= (float)gameTime.ElapsedGameTime.TotalSeconds;
if (delay < 0)
{
      int vertical = kbState.IsKeyDown(Keys.Up) ? -1 : kbState.IsKeyDown(Keys.Down) ? 1 : 0;
      int horizontal = kbState.IsKeyDown(Keys.Left) ? -1 : kbState.IsKeyDown(Keys.Right) ? 1 : 0;
      movement = new Vector2(horizontal, vertical);
      delay = DELAY;
}

character.Update(gameTime, movement);

Seems I have to use a delay in order to get this to work. Thanks for the feedback guys.

Answer 1

This is something I just worked on because I had similar issue in the past and the question made me curious to revisit it.

One thing to start with is to create your own utility class for handling Input that you can use on all future projects as the default methods with XNA are clumsy. You want methods as @Hackworth mentioned to detect when a key has been released/pressed/down that is easier to manage.

Within my Update Method for the character:

 var velocity = Vector2.Zero;

    // Notice that velocity persists through these keypresses and
    // keys are polled individually
 if (InputHandler.KeyDown(Keys.Up) && !InputHandler.KeyDown(Keys.Down))
     velocity = new Vector2(velocity.X, -1);
 if (InputHandler.KeyDown(Keys.Down) && !InputHandler.KeyDown(Keys.Up))
     velocity = new Vector2(velocity.X, 1);
 if (InputHandler.KeyDown(Keys.Right) && !InputHandler.KeyDown(Keys.Left))
     velocity = new Vector2(1, velocity.Y);
 if (InputHandler.KeyDown(Keys.Left) && !InputHandler.KeyDown(Keys.Right))
     velocity = new Vector2(-1, velocity.Y);

    // now that each part of the Vector2 is set to 0/1/-1 we can set an enum
    // Representing this Vector2's direction.
    SetDirection(velocity);

    // Now, within that tiny amount of time we might have released a key
    // which causes our character to annoy us with his orientation.
    // So, let's override with a more desired orientation.

    // Up_Right
    if (InputHandler.KeyDown(Keys.Up) && InputHandler.KeyReleased(Keys.Right))
        DrawDirection = Directions.UP_RIGHT;
    if (InputHandler.KeyDown(Keys.Right) && InputHandler.KeyReleased(Keys.Up))
        DrawDirection = Directions.UP_RIGHT;
    // Up_Left
    if (InputHandler.KeyDown(Keys.Up) && InputHandler.KeyReleased(Keys.Left))
        DrawDirection = Directions.UP_LEFT;
    if (InputHandler.KeyDown(Keys.Left) && InputHandler.KeyReleased(Keys.Up))
        DrawDirection = Directions.UP_LEFT;
    // Down_Right
    if (InputHandler.KeyDown(Keys.Down) && InputHandler.KeyReleased(Keys.Right))
        DrawDirection = Directions.DOWN_RIGHT;
    if (InputHandler.KeyDown(Keys.Right) && InputHandler.KeyReleased(Keys.Down))
        DrawDirection = Directions.DOWN_RIGHT;
    // Down_Left
    if (InputHandler.KeyDown(Keys.Down) && InputHandler.KeyReleased(Keys.Left))
        DrawDirection = Directions.DOWN_LEFT;
    if (InputHandler.KeyDown(Keys.Left) && InputHandler.KeyReleased(Keys.Down))
        DrawDirection = Directions.DOWN_LEFT;

    private void SetDirection(Vector2 direction)
    {
             if (direction.X == 0 && direction.Y == -1)
                DrawDirection = Directions.UP;
            else if (direction.X == 0 && direction.Y == 1)
                DrawDirection = Directions.DOWN;
            else if (direction.X == -1 && direction.Y == 0)
                DrawDirection = Directions.LEFT;
            else if (direction.X == 1 && direction.Y == 0)
                DrawDirection = Directions.RIGHT;
            else if (direction.X == -1 && direction.Y == -1)
                DrawDirection = Directions.UP_LEFT;
            else if (direction.X == -1 && direction.Y == 1)
                DrawDirection = Directions.DOWN_LEFT;
            else if (direction.X == 1 && direction.Y == -1)
                DrawDirection = Directions.UP_RIGHT;
            else if (direction.X == 1 && direction.Y == 1)
                DrawDirection = Directions.DOWN_RIGHT;
    }

Answer 2

What you need is to store the previous frame's keyboard state. Then determine which button has just been pressed compared to the previous state, and only if a button goes from released to pressed can it change the direction of your character. That way, you don't need to fiddle with artificial delays or anything.

Basically you want to implement the equivalent of the KeyDown event that you may know from a Forms or WPF UI application.

You could use this method:

    private bool keyWentDown(Keys key)
    {
        return kbState.IsKeyDown(key) && prevKbState.IsKeyUp(key);
    }

Basically you can re-use your code as it is. However, you don't execute it every frame, but only when your character direction actually needs updating, i.e. when any of the direction keys has been pressed.

So the complete code could be:

        if (keyWentDown(Keys.Up) 
            || keyWentDown(Keys.Down) 
            || keyWentDown(Keys.Left) 
            || keyWentDown(Keys.Right))
        {
            //your code
        }

Answer 3

Compare the last player position (differing from the current position) with the current position and don't take the arrow keys in account at all. I.e. only store the last position when actually a movement happens.

Assuming (y-axis pointing towards bottom):

if (x < lastX) {
    if (y < lastY) {
        // top left
    } else if (y == lastY) {
        // left
    } else { // y > lastY
        // bottom left
    }
} else if (x == lastX) {
    if (y < lastY) {
        // top
    } else if (y == lastY) {
        // Not allowed
    } else { // y > lastY
        // bottom
    }
} else { // x > lastX
    if (y < lastY) {
        // top right
    } else if (y == lastY) {
        // right
    } else { // y > lastY
        // bottom right
    }
}