Kav/Effects/SkyboxEffect.cs

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

namespace Kav
{
    public class SkyboxEffect : Effect
    {
        EffectParameter viewProjectionParam;
        EffectParameter skyboxParam;

        Matrix view;
        Matrix projection;
        TextureCube skybox;

        EffectDirtyFlags dirtyFlags = EffectDirtyFlags.All;

        public Matrix View
        {
            get { return view; }
            set 
            {
                view = value;
                dirtyFlags |= EffectDirtyFlags.WorldViewProj;
            }
        }

        public Matrix Projection
        {
            get { return projection; }
            set
            {
                projection = value;
                dirtyFlags |= EffectDirtyFlags.WorldViewProj;
            }
        }

        public TextureCube Skybox
        {
            get { return skybox; }
            set
            {
                skybox = value;
                dirtyFlags |= EffectDirtyFlags.World; // hack flag but whatever
            }
        }

        public SkyboxEffect(GraphicsDevice graphicsDevice) : base(graphicsDevice, Resources.SkyboxEffect)
        {
            CacheEffectParameters();
        }

        protected override void OnApply()
        {
            if ((dirtyFlags & EffectDirtyFlags.WorldViewProj) != 0)
            {
                Matrix.Multiply(ref view, ref projection, out Matrix viewProjection);

                viewProjectionParam.SetValue(viewProjection);

                dirtyFlags &= ~EffectDirtyFlags.WorldViewProj;
            }

            if ((dirtyFlags & EffectDirtyFlags.World) != 0)
            {
                skyboxParam.SetValue(skybox);

                dirtyFlags &= ~EffectDirtyFlags.World;
            }
        }

        private void CacheEffectParameters()
        {
            viewProjectionParam = Parameters["ViewProjection"];
            skyboxParam = Parameters["skybox"];
        }
    }
}