Getting wrong value for middle of screen

Question

My mouse is able to move the camera and rotate it around my model. If the mouse is in the middle of the screen, the camera should not move.

The red circle is where my mouse has to be at in order for the camera to stay still. If I put the cursor in the middle of the screen, it rotates the camera which shouldn't happen.

    Point screenCenter;
    float scrollRate = 1.0f;
    MouseState previousMouse;
    bool moveMode = false;

    #region MOUSE
        screenCenter.X = this.Window.ClientBounds.Width / 2;
        screenCenter.Y = this.Window.ClientBounds.Height / 2;

        this.IsMouseVisible = true;

        previousMouse = Mouse.GetState();
        Mouse.SetPosition(screenCenter.X, screenCenter.Y);
        #endregion MOUSE

    if (this.IsActive)
        {
            MouseState mouse = Mouse.GetState();

            if (moveMode)
            {
                Vector3 temp = player.playerWorld.Translation;
                player.playerWorld.Translation = Vector3.Zero;
                player.playerWorld *= Matrix.CreateRotationY(MathHelper.ToRadians(mouse.X - screenCenter.X) / 75);
                player.playerWorld.Translation = temp;

                cam.up -= MathHelper.ToRadians(mouse.Y - screenCenter.Y) / 25;
            }

            if (mouse.RightButton == ButtonState.Pressed)
            {
                if (graphics.GraphicsDevice.Viewport.Bounds.Contains(new Point(mouse.X, mouse.Y)))
                {
                    moveMode = true;
                }
            }
            else
            {
                if (moveMode)
                {
                    moveMode = false;
                }
            }

            if (mouse.ScrollWheelValue - previousMouse.ScrollWheelValue != 0)
            {
                float wheelChange = mouse.ScrollWheelValue - previousMouse.ScrollWheelValue;

                cam.up += 0.7f;
                cam.backward += 0.7f;
            }
            previousMouse = mouse;
        }

Why could this be happening? the screen is 650X1000. ScreenCenter x and y are the correct values.

Now that I play with it more, it seems each time the game starts, the mouse is set to a different position. The mouse should automatically be set to the middle of the screen each time the game starts, but it ends up anywhere but the middle.

Any idea of what could be happening here?

Answer 1

Here's your problem:

cam.up -= MathHelper.ToRadians(mouse.Y - screenCenter.Y) / 25;

You are setting the mouse to the center of the screen, but you are moving the screen in relation to the bottom corner of the screen, instead of the middle. Try changing it to:

cam.up -= MathHelper.ToRadians(mouse.Y - (screenCenter.Y / 2.0f)) / 25.0f;