HLSL Tips 1: Pseudo-random Number Generator

Preface
PRNG on the GPU. Two pseudo random numbers per iteration (from the BA channels). Inspired by Pete Warden's fragment program for pseudo-random number generation. In turn based on an algorithm described by Francois Grieu, sci.crypt, 5th February 2004. Implementd in Cg by Alex Campbell. 7th August 2006. Thanks for their works. I implement it in HLSL now.

Function

#define cMult 0.0001002707309736288
#define aSubtract 0.2727272727272727

float4 randGrieu(float4 t)
{

float a=t.x+t.z*cMult+aSubtract-floor(t.x);

a*=a;

float b=t.y+a;

b-=floor(b);

float c=t.z+b;

c-=floor(c);

float d=c;

a+=c*cMult+aSubtract-floor(a);

a*=a;

b+=a;

b-=floor(b);

c+=b;

c-=floor(c);

return float4(a,b,c,d);

}

Application

Code snippet:

float4 color=tex2D(TextureSampler, In.TexCoord0);

color=randGrieu(color);

Out.color=color;

The original texture is as follows:

After called randGrieu() once, the result texture is: