CODEWITHSUNDEEP
matrixxnacamera2d
user3170345
user3170345

Reputation: 11

XNA 2D Camera loosing precision

I have created a 2D camera (code below) for a top down game. Everything works fine when the players position is close to 0.0x and 0.0y.

Unfortunately as distance increases the transform seems to have problems, at around 0.0x 30e7y (yup that's 30 million y) the camera starts to shudder when the player moves (the camera gets updated with the player position at the end of each update) At really big distances, a billion + the camera wont even track the player, as I'm guessing what ever error is in the matrix is amplified by too much.

My question is: Is there either a problem in the matrix, or is this standard behavior for extreme numbers.

Camera Transform Method:

public Matrix getTransform()
{
    Matrix transform;

    transform = (Matrix.CreateTranslation(new Vector3(-position.X, -position.Y, 0)) *
            Matrix.CreateRotationZ(rotation) * Matrix.CreateScale(new Vector3(zoom, zoom, 1.0f)) *
    Matrix.CreateTranslation(new Vector3((viewport.Width / 2.0f), (viewport.Height / 2.0f), 0)));

    return transform;
}

Camera Update Method:

This requests the objects position given it's ID, it returns a basic Vector2 which is then set as the cameras position.

if (camera.CameraMode == Camera2D.Mode.Track && cameraTrackObject != Guid.Empty)
{
    camera.setFocus(quadTree.getObjectPosition(cameraTrackObject));                    
}

If any one can see an error or enlighten me as to why the matrix struggles I would be most grateful.

Upvotes: 1

Views: 103

Answers (1)

user3170345
user3170345

Reputation: 11

I have actually found the reason for this, it was something I should have thought of.

I'm using single precision floating points, which only have precision to 7 digits. That's fine for smaller numbers (up to around the 2.5 million mark I have found). Anything over this and the multiplication functions in the matrix start to gain precision errors as the floats start to truncate.

The best solution for my particular problem is to introduce some artificial scaling (I need the very large numbers as the simulation is set in space). I have limited my worlds to 5 million units squared (+/- 2.5 million units) and will come up with another way of granulating the world.

I also found a good answer about this here:

Vertices shaking with large camera position values

And a good article that discusses floating points in more detail:

What Every Computer Scientist Should Know About Floating-Point Arithmetic

Thank you for the views and comments!!

Upvotes: 0

Related Questions