C# XNA determine if Vector2 is facing another Vector2

Question

I'm working on a 2D game. I'm trying to figure out how to determine if one Vector2 is facing the other.

Here is what I have so far:

public void update(GameTime gameTime, Vector2 playerPosition)
{
    // position is "enemy" Vector2
    // rotationAngle is the angle which the "enemy" is facing
    // I need to determine if the "enemy" should rotate left, right, or move forward
    // The goal is to have the "enemy" move towards the player
    float angle = MathHelper.ToDegrees((float)Math.Atan2(playerPosition.Y - position.Y, playerPosition.X - position.X));
    float rotationDegrees = MathHelper.ToDegrees(rotationAngle);
    // Now what????





    update(gameTime);
}

Jared Price Jared Price · Accepted Answer · 2015-10-10T19:42:57

Gah, after just trying some stuff I figured it out.

public void update(GameTime gameTime, Vector2 playerPosition)
{
    float angle = MathHelper.ToDegrees((float)Math.Atan2(playerPosition.Y - position.Y, playerPosition.X - position.X));
    float rotationDegrees = MathHelper.ToDegrees(rotationAngle);
    var diff = ((rotationDegrees - angle) + 360) % 360;
    if (diff > 90)
    {
        // bool for rotate method determines if rotating left or right
        rotate(false);
    }
    else
    {
        rotate(true);
    }

    if (diff < 180 && diff > 0)
    {
        moveForward();
    }

    update(gameTime);
}

Edit: there were some issues with my calculations. Under certain conditions, enemies would get stuck. The issue is that sometimes the value would change from a negative to a positive value with every game update. The solution was to make sure diff was always positive.

C# XNA determine if Vector2 is facing another Vector2

1 Answers