A 3D game engine you write in C#.

class PauseWindow : Window
{
    private readonly RendererViewport _viewport = new();

    public PauseWindow()
    {
        // The pause menu is a StackPanel.
        var menu = new StackPanel
        {
            HorizontalAlignment = HorizontalAlignment.Left,
            VerticalAlignment = VerticalAlignment.Center,
            Children =
            {
                new Button { Content = "Resume" },
                new Button { Content = "Quit" },
            },
        };

        // Whatever comes after the viewport in the children is drawn over it.
        Content = new Grid { Children = { _viewport, menu } };
    }

    private void Draw(double seconds) =>
        _viewport.Frame(new RenderScene
        {
            Camera = new RenderCamera
            {
                Position = new Vector3(0, 3, 8),
                Target = Vector3.Zero(),
            },
            Objects =
            [
                new RenderObject
                {
                    Key = 1,
                    Transform = Matrix4.Identity(),
                    Colour = new Vector3(0.85, 0.42, 0.16),
                },
            ],
        }, seconds);
}