Question

I have the model representing the player’s ship gradually leaning when the player strafes. For instance, here’s the code that leans the ship right:

In Update() of the Game class:

if (ship.rightTurnProgress < 1 && (currentKeyState.IsKeyDown(Keys.D)))
{
    ship.rightTurnProgress += (float)gameTime.ElapsedGameTime.TotalSeconds * 30;
}

In Update() of the Ship class:

if (currentKeyState.IsKeyDown(Keys.D))
{
   Velocity += Vector3.Right * VelocityScale * 10.0f;
   RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) * 
     Matrix.CreateRotationY(0.4f * rightTurnProgress);
}

This is what I’m attempting to do to make it ease back out of the lean when it stops strafing:

In Update() of the Game class:

if (ship.rightTurnProgress > 0 && currentKeyState.IsKeyUp(Keys.D))
{
    ship.rightTurnProgress -= (float)gameTime.ElapsedGameTime.TotalSeconds * 30;
}

In Update() of the Ship class:

if (currentKeyState.IsKeyUp(Keys.D) && rightTurnProgress > 0)
{
    RotationMatrix = Matrix.CreateRotationX(MathHelper.PiOver2) *
      Matrix.CreateRotationY(-0.4f * rightTurnProgress);
}

Since easing into the lean works no problem, I thought easing out of the lean would be a simple matter of reversing the process. However, it tends to not go all the way back to the default position after a long strafe. If you tap the key, it snaps all the way back to the full lean of the -opposite- direction. This isn’t what I expected at all. What am I missing here?

Answer 1

I suggest you represent the rotation of you ship as a quaternion. That way you can use an interpolation function such as slerp. Simply have a second quaternion that represents you targeted lean angle and the ship will smoothly rotate until it achieves the targeted angle.

Here’s a good tutorial on quaternions. If you want to avoid quaternions use MathHelper.Lerp to smoothly transition from the current value to the target.

if (currentKeyState.IsKeyDown(Keys.D))
{
    ship.TurnProgress = MathHelper.Lerp(ship.TurnProgress, 1, somefloat * timeDelta);
}
else if (currentKeyState.IsKeyDown(Keys.a))
{
    ship.TurnProgress = MathHelper.Lerp(ship.TurnProgress, -1, somefloat * timeDelta);
}
else  (currentKeyState.IsKeyDown(Keys.D))
{
    ship.TurnProgress = MathHelper.Lerp(ship.TurnProgress, 0, somefloat * timeDelta);
}

Edit: Also there is a GameDev stack overflow so check it out if you have more questions.