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

namespace Kav
{
    public class SimpleDepthEffect : Effect
    {
        EffectParameter modelViewProjectionParam;
        EffectParameter nearParam;
        EffectParameter farParam;

        Matrix model;
        Matrix view;
        Matrix projection;

        EffectDirtyFlags dirtyFlags = EffectDirtyFlags.All;

        public Matrix Model
        {
            get { return model; }
            set
            {
                model = value;
                dirtyFlags |= EffectDirtyFlags.WorldViewProj;
            }
        }

        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 float Near { get; set; }
        public float Far { get; set; }

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

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

                modelViewProjectionParam.SetValue(worldViewProj);

                dirtyFlags &= ~EffectDirtyFlags.WorldViewProj;
            }

            nearParam.SetValue(Near);
            farParam.SetValue(Far);
        }

        private void CacheEffectParameters()
        {
            modelViewProjectionParam = Parameters["ModelViewProjection"];
            nearParam = Parameters["near"];
            farParam = Parameters["far"];
        }
    }
}