XNA Hack: Create RenderTarget2D greater than 4096x4096

Problem:

XNA's HiDef profile has a maximum Texture2D size of 4096x4096.  RenderTarget2D has a backing Texture2D object, and this limitation is enforced at time of construction.

Solution:

Time to get a bit tricky with reflection.  Limitations in XNA are all stored in Microsoft.Xna.Framework.Graphics.ProfileCapabilities, an internal class.  Fortunately, they aren't constants...

In your Initialize() function...

Assembly xna = Assembly.GetAssembly(typeof(GraphicsProfile));
Type profileCapabilities = xna.GetType("Microsoft.Xna.Framework.Graphics.ProfileCapabilities", true);
if (profileCapabilities != null)
{
     FieldInfo maxTextureSize = profileCapabilities.GetField("MaxTextureSize", BindingFlags.Instance | BindingFlags.NonPublic);
     FieldInfo hidefProfile = profileCapabilities.GetField("HiDef", BindingFlags.Static | BindingFlags.NonPublic);
     if (maxTextureSize != null && hidefProfile != null)
     {
         object profile = hidefProfile.GetValue(null);
         maxTextureSize.SetValue(hidefProfile.GetValue(null), MaxTextureSize);
     }
}

Replace MaxTextureSize in the last line with whatever you feel your maximum size should be. Ideally, you'll be querying DirectX 9 and setting the value to the maximum value allowed by D3D9Caps.