} // Lerp

        #endregion

        #region Generate Spherical Harmonic from CubeMap

        /// <summary>
        /// Generate a spherical harmonic from the faces of a cubemap, treating each pixel as a light source and averaging the result.
        /// This method only accepts RGBM and color textures.
        /// </summary>
        public static SphericalHarmonicL2 GenerateSphericalHarmonicFromCubeTexture(TextureCube cubeTexture)
        {
            if (cubeTexture.Resource.Format != SurfaceFormat.Color)
            {
                throw new InvalidOperationException("Spherical Harmonic: the texture has to have a color surface format. DXT and floating point formats are not supported for the moment.");
            }

            SphericalHarmonicL2 sh = new SphericalHarmonicL2();

            // Extract the 6 faces of the cubemap.
            for (int face = 0; face < 6; face++)
            {
                CubeMapFace faceId = (CubeMapFace)face;

                // Get the transformation for this face.
                Matrix cubeFaceMatrix;
                switch (faceId)
                {
                case CubeMapFace.PositiveX:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(1, 0, 0), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.NegativeX:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(-1, 0, 0), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.PositiveY:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 1, 0), new Vector3(0, 0, 1));
                    break;

                case CubeMapFace.NegativeY:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, -1, 0), new Vector3(0, 0, -1));
                    break;

                case CubeMapFace.PositiveZ:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.NegativeZ:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 0, 1), new Vector3(0, 1, 0));
                    break;

                default:
                    throw new ArgumentOutOfRangeException();
                }
                Color[] colorArray = new Color[cubeTexture.Size * cubeTexture.Size];
                cubeTexture.Resource.GetData(faceId, colorArray);

                // Extract the spherical harmonic for this face and accumulate it.
                sh += ExtractSphericalHarmonicForCubeFace(cubeFaceMatrix, colorArray, cubeTexture.Size, cubeTexture.IsRgbm, cubeTexture.RgbmMaxRange);
            }

            // Average out over the sphere.
            return(sh.GetWeightedAverageLightInputFromSphere());
        } // GenerateSphericalHarmonicFromCubeTexture
        } // SampleDirection

        #endregion

        #region Generate Spherical Harmonic from CubeMap

        /// <summary>
        /// Generate a spherical harmonic from the faces of a cubemap, treating each pixel as a light source and averaging the result.
        /// </summary>
        public static SphericalHarmonicL1 GenerateSphericalHarmonicFromCubeMap(TextureCube cubeMap)
        {
            SphericalHarmonicL1 sh = new SphericalHarmonicL1();

            // Extract the 6 faces of the cubemap.
            for (int face = 0; face < 6; face++)
            {
                CubeMapFace faceId = (CubeMapFace)face;

                // Get the transformation for this face,
                Matrix cubeFaceMatrix;
                switch (faceId)
                {
                case CubeMapFace.PositiveX:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(1, 0, 0), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.NegativeX:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(-1, 0, 0), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.PositiveY:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 1, 0), new Vector3(0, 0, 1));
                    break;

                case CubeMapFace.NegativeY:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, -1, 0), new Vector3(0, 0, -1));
                    break;

                case CubeMapFace.PositiveZ:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), new Vector3(0, 1, 0));
                    break;

                case CubeMapFace.NegativeZ:
                    cubeFaceMatrix = Matrix.CreateLookAt(Vector3.Zero, new Vector3(0, 0, 1), new Vector3(0, 1, 0));
                    break;

                default:
                    throw new ArgumentOutOfRangeException();
                }
                Color[] colorArray = new Color[cubeMap.Size * cubeMap.Size];
                cubeMap.Resource.GetData <Color>(faceId, colorArray);

                // Extract the spherical harmonic for this face and accumulate it.
                sh += ExtractSphericalHarmonicForCubeFace(cubeFaceMatrix, colorArray, cubeMap.Size, cubeMap.IsRgbm, cubeMap.RgbmMaxRange);
            }

            //average out over the sphere
            return(sh.GetWeightedAverageLightInputFromSphere());
        } // GenerateSphericalHarmonicFromCubeMap
Exemple #3
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        } // Begin

        #endregion

        #region Render

        /// <summary>
        /// Render the point light.
        /// </summary>
        public void Render(Color diffuseColor, Vector3 position, float intensity, float radius, TextureCube shadowTexture, Matrix worldMatrix, bool renderClipVolumeInLocalSpace, Model clipVolume = null)
        {
            try
            {
                // It is possible to use the depth information and the stencil buffer to mark in a two pass rendering exactly what pixels are affected by the light.
                // This helps to reduce pixel shader load but at the same time allows implementing clip volumes.
                // With clip volumes you can put, for example, a box and the light won’t bleed outside this box even if the radius is bigger.
                // I.e. you can place lights in a wall and the opposite side of that wall won’t be illuminated.
                //
                // The problem is I don’t have the Z-Buffer available because XNA 4 does not allow sharing depth buffers between render targets.
                // However I can reconstruct the Z-Buffer with a shader and my G-Buffer.
                //
                // If you don’t use custom clip volumes (i.e. we use the default sphere) and the light is too far then we could have more vertex processing
                // than pixel processing. Some games use glow planes (a colored mask) to see the light’s bright when they are far away,
                // this is good for open environment games but not for interior games.
                // Instead games like Killzone 2 ignore the first pass on these lights and only compute the second (and this second pass still does one
                // part of the filter). Also the far plane "problem" is addressed in this optimization.
                //
                // Another optimization that I made is the use of a Softimage sphere instead of my procedural spheres.
                // Models exported in this kind of tools are optimized for accessing. For example my stress test changes from 20/21 frames to 22 frames.
                // Not a big change, but still a change nevertheless.
                //
                // I also research the possibility to use instancing with some lights.
                // But no article talk about this technique so I try to think why is not useful and it was easy to find that:
                // 1) It can be only used with spheres (not custom clip volumes).
                // 2) The dynamic buffers used for the instancing information could be too dynamic or difficult to maintain.
                // 3) The stencil optimization could be very important on interior games and could not be mixed with instancing and custom clip volumes.
                // Extra complexity added (including the use of vfetch for Xbox 360).

                // Fill the stencil buffer with 0s.
                EngineManager.Device.Clear(ClearOptions.Stencil, Color.White, 1.0f, 0);

                #region Set Parameters

                spLightColor.Value     = diffuseColor;
                spLightPosition.Value  = Vector3.Transform(position, viewMatrix);
                spLightIntensity.Value = intensity;
                spInvLightRadius.Value = 1 / radius;

                if (shadowTexture != null)
                {
                    spShadowTexture.Value  = shadowTexture;
                    spViewInverse.Value    = Matrix.Invert(Matrix.Transpose(Matrix.Invert(viewMatrix)));
                    spTextureSize.Value    = new Vector3(shadowTexture.Size, shadowTexture.Size, shadowTexture.Size);
                    spTextureSizeInv.Value = new Vector3(1.0f / shadowTexture.Size, 1.0f / shadowTexture.Size, 1.0f / shadowTexture.Size);
                }
                else
                {
                    spShadowTexture.Value = TextureCube.BlackTexture;
                }

                // Compute the light world matrix.
                Matrix boundingLightObjectWorldMatrix;
                if (clipVolume != null)
                {
                    boundingLightObjectWorldMatrix = renderClipVolumeInLocalSpace ? Matrix.Identity : worldMatrix;
                }
                else
                {
                    // Scale according to light radius, and translate it to light position.
                    boundingLightObjectWorldMatrix = Matrix.CreateScale(radius) * Matrix.CreateTranslation(position);
                }

                spWorldViewProj.Value = boundingLightObjectWorldMatrix * viewMatrix * projectionMatrix;
                spWorldView.Value     = boundingLightObjectWorldMatrix * viewMatrix;

                #endregion

                // http://en.wikipedia.org/wiki/Angular_diameter
                // The formula was inspired from Guerilla´s GDC 09 presentation.
                float distanceToCamera = Vector3.Distance(Matrix.Invert(viewMatrix).Translation, position);
                float angularDiameter  = (float)(2 * Math.Atan(radius / distanceToCamera));
                if (angularDiameter > 0.2f * (3.1416f * fieldOfView / 180.0f)) // 0.2f is the original value.
                {
                    // This only works when the clip volume does not intercept the camera´s far plane.

                    // First pass.
                    // The stencil buffer was already filled with 0 and if the back of the clip volume
                    // is in front of the geometry then it marks the pixel as useful.
                    // I prefer to do it in that way because when the clip volume intercept the camera’s near plane
                    // we don’t need to perform a special case and we still have custom volume support.
                    Resource.CurrentTechnique              = pointLightStencilTechnique;
                    EngineManager.Device.RasterizerState   = RasterizerState.CullCounterClockwise;
                    EngineManager.Device.BlendState        = stencilBlendState;
                    EngineManager.Device.DepthStencilState = stencilDepthStencilState;
                    Resource.CurrentTechnique.Passes[0].Apply();
                    if (clipVolume != null)
                    {
                        clipVolume.Render();
                    }
                    else
                    {
                        boundingLightObject.Render();
                    }

                    // Second pass.
                    // Render the clip volume back faces with the light shader.
                    // The pixel with stencil value of 1 that are in front of the geometry will be discarded.
                    Resource.CurrentTechnique              = shadowTexture != null ? pointLightWithShadowsTechnique : pointLightTechnique;
                    EngineManager.Device.RasterizerState   = RasterizerState.CullClockwise;
                    EngineManager.Device.BlendState        = lightBlendState;
                    EngineManager.Device.DepthStencilState = lightDepthStencilState;
                    Resource.CurrentTechnique.Passes[0].Apply();
                    if (clipVolume != null)
                    {
                        clipVolume.Render();
                    }
                    else
                    {
                        boundingLightObject.Render();
                    }
                }
                else // Far lights
                {
                    // Render the clip volume front faces with the light shader.
                    Resource.CurrentTechnique            = shadowTexture != null ? pointLightWithShadowsTechnique : pointLightTechnique;
                    EngineManager.Device.RasterizerState = RasterizerState.CullCounterClockwise;
                    //EngineManager.Device.BlendState = lightBlendState; // Not need to set it.
                    EngineManager.Device.DepthStencilState = DepthStencilState.DepthRead;
                    Resource.CurrentTechnique.Passes[0].Apply();
                    if (clipVolume != null)
                    {
                        clipVolume.Render();
                    }
                    else
                    {
                        boundingLightObject.Render();
                    }
                }
            }
            catch (Exception e)
            {
                throw new InvalidOperationException("Light Pre Pass Point Light: Unable to render.", e);
            }
        } // Render