} // 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
} // ExtractSphericalHarmonicForCubeFace
#endregion
#region Generate Spherical Harmonic from Lat-Long Texture
/// <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 floating point textures.
/// </summary>
public static SphericalHarmonicL2 GenerateSphericalHarmonicFromLatLongTexture(Texture texture)
{
if (texture.Resource.Format != SurfaceFormat.Vector4)
{
throw new InvalidOperationException("Spherical Harmonic: the texture has to have a floating point surface format. DXT formats are not supported for the moment.");
}
SphericalHarmonicL2 sh = new SphericalHarmonicL2();
float[] colorArray = new float[texture.Width * texture.Height * 4];
texture.Resource.GetData(colorArray);
int pixelIndex = 0;
for (int y = 0; y < texture.Height; y++)
{
SphericalHarmonicL2 lineSh = new SphericalHarmonicL2();
for (int x = 0; x < texture.Width; x++)
{
// http://www.scratchapixel.com/lessons/3d-advanced-lessons/reflection-mapping/converting-latitute-longitude-maps-and-mirror-balls/
float theta = (x / (float)texture.Width) * (float)Math.PI;
float phi = (1 - (y / (float)texture.Height)) * 2 * (float)Math.PI;
Vector3 direction = -new Vector3((float)(Math.Sin(theta) * Math.Cos(phi)), (float)(Math.Sin(theta) * Math.Sin(phi)), (float)(Math.Cos(theta)));
direction.Normalize();
Vector3 rgb = new Vector3(colorArray[pixelIndex * 4], colorArray[pixelIndex * 4 + 1], colorArray[pixelIndex * 4 + 2]);
//Add it to the SH
lineSh.AddLight(rgb, direction, 1);
pixelIndex++;
}
//average the SH
if (lineSh.weighting > 0)
{
lineSh *= 1 / lineSh.weighting;
}
// Add the line to the full SH
// (SH is generated line by line to ease problems with floating point accuracy loss)
sh += lineSh;
}
//average out over the sphere
return(sh.GetWeightedAverageLightInputFromSphere());
} // GenerateSphericalHarmonicFromLatLongHdrTexture