/**
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* Computes a color from the third order spherical harmonic coefficients and a normalized direction vector.
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* <p>
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* The order of the coefficients is [L00, L1_1, L10, L11, L2_2, L2_1, L20, L21, L22].
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* </p>
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*
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* @name czm_sphericalHarmonics
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* @glslFunction
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*
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* @param {vec3} normal The normalized direction.
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* @param {vec3[9]} coefficients The third order spherical harmonic coefficients.
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* @returns {vec3} The color at the direction.
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*
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* @see https://graphics.stanford.edu/papers/envmap/envmap.pdf
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*/
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vec3 czm_sphericalHarmonics(vec3 normal, vec3 coefficients[9])
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{
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vec3 L00 = coefficients[0];
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vec3 L1_1 = coefficients[1];
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vec3 L10 = coefficients[2];
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vec3 L11 = coefficients[3];
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vec3 L2_2 = coefficients[4];
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vec3 L2_1 = coefficients[5];
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vec3 L20 = coefficients[6];
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vec3 L21 = coefficients[7];
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vec3 L22 = coefficients[8];
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float x = normal.x;
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float y = normal.y;
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float z = normal.z;
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return
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L00
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+ L1_1 * y
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+ L10 * z
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+ L11 * x
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+ L2_2 * (y * x)
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+ L2_1 * (y * z)
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+ L20 * (3.0 * z * z - 1.0)
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+ L21 * (z * x)
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+ L22 * (x * x - y * y);
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}
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