Accelerate a Bullet on The Right Direction

Question

I'm creating a simple asteroids 2D game with XNA so I can learn more on game development, I've started by reading this tutorial and, with my previous knowledge from developing Windows Phone applications, I've started changing the code. I've designed a simple isosceles triangle that is rotated with the accelerometer, like this:

private void CurrentValueChanged(MotionReading e)
{
    // Check to see if the Motion data is valid.
    if (motion.IsDataValid)
    {
        triangle.Update(MathHelper.ToDegrees(e.Attitude.Yaw));
        System.Diagnostics.Debug.WriteLine("Yaw: " + MathHelper.ToDegrees(e.Attitude.Yaw));
        System.Diagnostics.Debug.WriteLine("Angle: " + triangle.getAngle());
    }
}

The triangle.Update just changes the batch.Draw rotation parameter.

I'm also creating a "bullet", when the user clicks on the screen, using a circle texture, what I want to know is how I can point this "bullet" to the direction that the triangle sprite is heading.

PS: The triangle "point", where the bullet should be fired, is exactly the width / 2.

Answer 1

That's (below) standard geometry: As you rotate the triangle from its initial position using the angle you got from user input, you can also define the shooting vector direction MC where M is the middle of the base (width/2) and C is the opposite vertex of the triangle. Rotating the triangle will automatically rotate the shooting direction.