auto letterboxing

Resolution.cs

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace IndependentResolutionRendering
{
    static class Resolution
    {
        static private int s_virtual_width;
        static private int s_virtual_height;
        static private int s_screen_width;
        static private int s_screen_height;

        static private Matrix s_transform_matrix;
        static private bool s_dirtyMatrix = true;

        static public void Init(int screenWidth, int screenHeight, int virtualWidth, int virtualHeight)
        {
            s_screen_width = screenWidth;
            s_screen_height = screenHeight;
            s_virtual_width = virtualWidth;
            s_virtual_height = virtualHeight;
            s_dirtyMatrix = true;
        }

        static public Matrix TransformMatrix
        {
            get
            {
                if (s_dirtyMatrix) RecreateScaleMatrix();
                return s_transform_matrix;
            }
        }

        static public void SetScreenResolution(int width, int height)
        {
            s_screen_width = width;
            s_screen_height = height;
            s_dirtyMatrix = true;
        }

        static public void SetVirtualResolution(int width, int height)
        {
            s_virtual_width = width;
            s_virtual_height = height;
            s_dirtyMatrix = true;
        }

        static private void RecreateScaleMatrix()
        {
            var scaleUniform = System.Math.Min(
                (float)s_screen_width / s_virtual_width,
                (float)s_screen_height / s_virtual_height
            );

            var scaleMatrix = Matrix.CreateScale(
                (float)scaleUniform,
                (float)scaleUniform,
                1f
            );

            var offX = (s_screen_width - scaleUniform * s_virtual_width) / 2;
            var offY = (s_screen_height - scaleUniform * s_virtual_height) / 2;
            var translationMatrix = Matrix.CreateTranslation(offX, offY, 0);

            s_transform_matrix = scaleMatrix * translationMatrix;
            s_dirtyMatrix = false;
        }
    }
}