NB: comment/uncomment block to switch between value/grad noise & linear/cubic interpolation
NB2: output range 0-255 => inded you can multiply by 1.0/256.0 to get usual double output
public class FastNoise
{
public static int noise(double x,double y,int nbOctave)
{
int result=0;
int frequence256=256;
int sx=(int)((x)*frequence256);
int sy=(int)((y)*frequence256);
int octave=nbOctave;
while(octave!=0)
{
int bX=sx&0xFF;
int bY=sy&0xFF;
int sxp=sx>>8;
int syp=sy>>8;
//Compute noise for each corner of current cell
int Y1376312589_00=syp*1376312589;
int Y1376312589_01=Y1376312589_00+1376312589;
int XY1376312589_00=sxp+Y1376312589_00;
int XY1376312589_10=XY1376312589_00+1;
int XY1376312589_01=sxp+Y1376312589_01;
int XY1376312589_11=XY1376312589_01+1;
int XYBASE_00=(XY1376312589_00<<13)^XY1376312589_00;
int XYBASE_10=(XY1376312589_10<<13)^XY1376312589_10;
int XYBASE_01=(XY1376312589_01<<13)^XY1376312589_01;
int XYBASE_11=(XY1376312589_11<<13)^XY1376312589_11;
int alt1=(XYBASE_00 * (XYBASE_00 * XYBASE_00 * 15731 + 789221) + 1376312589) ;
int alt2=(XYBASE_10 * (XYBASE_10 * XYBASE_10 * 15731 + 789221) + 1376312589) ;
int alt3=(XYBASE_01 * (XYBASE_01 * XYBASE_01 * 15731 + 789221) + 1376312589) ;
int alt4=(XYBASE_11 * (XYBASE_11 * XYBASE_11 * 15731 + 789221) + 1376312589) ;
/*
*NOTE : on for true grandiant noise uncomment following block
* for true gradiant we need to perform scalar product here, gradiant vector are created/deducted using
* the above pseudo random values (alt1...alt4) : by cutting thoses values in twice values to get for each a fixed x,y vector
* gradX1= alt1&0xFF
* gradY1= (alt1&0xFF00)>>8
*
* the last part of the PRN (alt1&0xFF0000)>>8 is used as an offset to correct one of the gradiant problem wich is zero on cell edge
*
* source vector (sXN;sYN) for scalar product are computed using (bX,bY)
*
* each four values must be replaced by the result of the following
* altN=(gradXN;gradYN) scalar (sXN;sYN)
*
* all the rest of the code (interpolation+accumulation) is identical for value & gradiant noise
*/
/*START BLOCK FOR TRUE GRADIANT NOISE*/
int grad1X=(alt1&0xFF)-128;
int grad1Y=((alt1>>8)&0xFF)-128;
int grad2X=(alt2&0xFF)-128;
int grad2Y=((alt2>>8)&0xFF)-128;
int grad3X=(alt3&0xFF)-128;
int grad3Y=((alt3>>8)&0xFF)-128;
int grad4X=(alt4&0xFF)-128;
int grad4Y=((alt4>>8)&0xFF)-128;
int sX1=bX>>1;
int sY1=bY>>1;
int sX2=128-sX1;
int sY2=sY1;
int sX3=sX1;
int sY3=128-sY1;
int sX4=128-sX1;
int sY4=128-sY1;
alt1=(grad1X*sX1+grad1Y*sY1)+16384+((alt1&0xFF0000)>>9); //to avoid seams to be 0 we use an offset
alt2=(grad2X*sX2+grad2Y*sY2)+16384+((alt2&0xFF0000)>>9);
alt3=(grad3X*sX3+grad3Y*sY3)+16384+((alt3&0xFF0000)>>9);
alt4=(grad4X*sX4+grad4Y*sY4)+16384+((alt4&0xFF0000)>>9);
/*END BLOCK FOR TRUE GRADIANT NOISE */
/*START BLOCK FOR VALUE NOISE*/
/*
alt1&=0xFFFF;
alt2&=0xFFFF;
alt3&=0xFFFF;
alt4&=0xFFFF;
*/
/*END BLOCK FOR VALUE NOISE*/
/*START BLOCK FOR LINEAR INTERPOLATION*/
//BiLinear interpolation
/*
int f24=(bX*bY)>>8;
int f23=bX-f24;
int f14=bY-f24;
int f13=256-f14-f23-f24;
int val=(alt1*f13+alt2*f23+alt3*f14+alt4*f24);
*/
/*END BLOCK FOR LINEAR INTERPOLATION*/
//BiCubic interpolation ( in the form alt(bX) = alt[n] - (3*bX^2 - 2*bX^3) * (alt[n] - alt[n+1]) )
/*START BLOCK FOR BICUBIC INTERPOLATION*/
int bX2=(bX*bX)>>8;
int bX3=(bX2*bX)>>8;
int _3bX2=3*bX2;
int _2bX3=2*bX3;
int alt12= alt1 - (((_3bX2 - _2bX3) * (alt1-alt2)) >> 8);
int alt34= alt3 - (((_3bX2 - _2bX3) * (alt3-alt4)) >> 8);
int bY2=(bY*bY)>>8;
int bY3=(bY2*bY)>>8;
int _3bY2=3*bY2;
int _2bY3=2*bY3;
int val= alt12 - (((_3bY2 - _2bY3) * (alt12-alt34)) >> 8);
val*=256;
/*END BLOCK FOR BICUBIC INTERPOLATION*/
//Accumulate in result
result+=(val<<octave);
octave--;
sx<<=1;
sy<<=1;
}
return result>>>(16+nbOctave+1);
}
}