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Magic Numbers [R2VB]

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Ok I was looking at the R2VB particle system sample from the ATI Radeon SDK and happen to notice a set of magic numbers when the author tried to calculate a higher precision order random value. //initPhysics.shd
float rand0 = tex2D(Rand, -texCoord).w;
float rand1 = tex2D(Rand, 10.2428 * texCoord).w;
float rand2 = tex2D(Rand, -4.724 * texCoord).w;
float rand3 = tex2D(Rand, 0.5128 * texCoord).w;
//create a higher precision random value from the four 16bit values
float rand = frac(8.0 * rand0 + 4.0 * rand1 + 2.0 * rand2 + rand3);

The magic numbers I am referring to are the -texCoord,10.2428,etc... Somehow I did have the feeling that there were precomputed instead. Does anyone know how the author arrived at such numbers?? I also checked, the "Rand" texture isnt clamped. thx! Edwin

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