public override void Draw(GameTime gameTime, SpriteBatch spriteBatch)
        {
            base.Draw(gameTime, spriteBatch);

            GraphicsDevice.SetRenderTarget(renderTargetA);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            Material material = new Material();
            material.DiffuseColor = Color.Red;
            material.AmbientColor = Color.Red;
            material.AmbientIntensity = 0.2f;
            material.SpecularColor = Color.White;
            material.SpecularIntensity = 2.0f;
            material.SpecularPower = 25.0f;

            #region Billboard
            GraphicsDevice.DepthStencilState = DepthStencilState.None;

            Matrix billboardMatrix = Matrix.CreateBillboard(lightPositions[0], camera.Eye, camera.Up, camera.Focus - camera.Eye);

            this.camera.SetEffectParameters(billboard);
            billboard.Parameters["World"].SetValue(world * billboardMatrix);
            billboard.Parameters["Tex"].SetValue(lightTexture);
            billboard.CurrentTechnique = billboard.Techniques["Technique1"];

            foreach (EffectPass pass in billboard.CurrentTechnique.Passes)
            {
                pass.Apply();
                this.GraphicsDevice.DrawUserIndexedPrimitives<VertexPositionNormalTexture>(PrimitiveType.TriangleList, lightQuad.QuadVertices, 0, lightQuad.QuadVertices.Length, lightQuad.QuadIndices, 0, lightQuad.QuadIndices.Length / 3);
            }

            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            #endregion

            #region OcclusionMap
            Effect tempEffect;
            foreach (ModelData m in models)
            {
                tempEffect = m.Model.Meshes[0].MeshParts[0].Effect;
                m.Model.Meshes[0].MeshParts[0].Effect = occlusion;

                ModelMesh mesh = m.Model.Meshes[0];

                occlusion.CurrentTechnique = occlusion.Techniques["Technique1"];
                this.camera.SetEffectParameters(occlusion);
                occlusion.Parameters["World"].SetValue(world * m.Transform);

                mesh.Draw();

                m.Model.Meshes[0].MeshParts[0].Effect = tempEffect;
            }
            #endregion

            #region PostProcessing
            GraphicsDevice.SetRenderTarget(null);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            Matrix projection = Matrix.CreateOrthographicOffCenter(0,
            GraphicsDevice.Viewport.Width, GraphicsDevice.Viewport.Height, 0, 0, 1);
            Matrix halfPixelOffset = Matrix.CreateTranslation(-0.5f, -0.5f, 0);
            postProcessing.Parameters["MatrixTransform"].SetValue(halfPixelOffset * projection);

            postProcessing.CurrentTechnique = postProcessing.Techniques["Godrays"];
            Vector3 lightPosition = Vector3.Transform(lightPositions[0], world * camera.ViewMatrix * camera.ProjectionMatrix);
            postProcessing.Parameters["lightPosition"].SetValue(new Vector2(lightPosition.X, lightPosition.Y));
            postProcessing.Parameters["Tex"].SetValue(renderTargetA);
            postProcessing.Parameters["exposure"].SetValue(0.2f);
            postProcessing.Parameters["decay"].SetValue(0.999f);
            postProcessing.Parameters["weight"].SetValue(0.2f);
            postProcessing.Parameters["density"].SetValue(0.9f);

            spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.Additive, SamplerState.PointWrap, DepthStencilState.Default, RasterizerState.CullNone, postProcessing);
            spriteBatch.Draw(renderTargetA, new Rectangle(spriteBatch.GraphicsDevice.Viewport.X, spriteBatch.GraphicsDevice.Viewport.Y, spriteBatch.GraphicsDevice.Viewport.Width, spriteBatch.GraphicsDevice.Viewport.Height), Color.White);
            spriteBatch.End();

            GraphicsDevice.BlendState = BlendState.Opaque;
            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;
            #endregion

            #region BlinnPhong
            GraphicsDevice.SetRenderTarget(renderTargetB);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            foreach (ModelData m in models)
            {
                ModelMesh mesh = m.Model.Meshes[0];
                Effect e = mesh.Effects[0];

                e.CurrentTechnique = e.Techniques[m.Technique];
                material.SetEffectParameters(e);
                this.camera.SetEffectParameters(e);
                e.Parameters["World"].SetValue(world * m.Transform);
                e.Parameters["WorldInverseTransposed"].SetValue(Matrix.Transpose(Matrix.Invert(world * m.Transform)));
                e.Parameters["CameraEye"].SetValue(new Vector4(this.camera.Eye, 0));
                // TODO: LightSource Color + Intensity
                e.Parameters["LightSources"].SetValue(lightPositions);

                mesh.Draw();
            }
            #endregion

            #region Drawing
            GraphicsDevice.SetRenderTarget(null);
            GraphicsDevice.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.Black, 1.0f, 0);

            spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.Additive);
            spriteBatch.Draw(renderTargetB, new Rectangle(spriteBatch.GraphicsDevice.Viewport.X, spriteBatch.GraphicsDevice.Viewport.Y, spriteBatch.GraphicsDevice.Viewport.Width, spriteBatch.GraphicsDevice.Viewport.Height), Color.White);
            spriteBatch.End();

            GraphicsDevice.BlendState = BlendState.Opaque;
            GraphicsDevice.DepthStencilState = DepthStencilState.Default;
            GraphicsDevice.SamplerStates[0] = SamplerState.LinearWrap;
            #endregion
        }