Moisaic Noise
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Download: Noise.h Noise.cpp		Mosaic Perlin Simplex Voronoi

The simplest noise texture is random rectangular areas. It is easy to overlook patterns like this, but occasionally some part of one of the images created may be exactly what you need as a basis for something more complex. The Textures page shows a floor tile being made from apparently unrelated gradients. Noise has a MosaicNoise methods which take three coordinates to create repeatable distortable images. The following code produced the above image; you can see the different x and y scales and the constant z:

  for(WORD x=GetWidth(); x--; ) { // Loops are best comparing the counter with zero, so this counts down.
    double u=double(x)/Width; // Calculate the parameter (ratio in the range [0,1]) indicating how far through the loop is.
    for(DWORD y=GetHeight(); y--;) {
      double v=double(y)/GetHeight(); // Calculate the parameter (ratio in the range [0,1]) indicating how far through the loop is.
      BYTE B=BYTE(Round(255*Noise::UnsignedMosaic(u*10, v*20, 0.5))); // Turn the parameter into a Greyscale Level.
      SetPixel(x,y, RGB(B,B,B));
  } }

GetWidth(), GetHeight() and SetPixel are members of CPixelBlock which was used as a base class.
Round is declared in Global.h.

The function given to the z parameter can be varied, and the mixed octaves idea (described on the Psuedo Random Number Generator (PRNG) page) can be implemented (with the following code):

  for(WORD x=GetWidth(); x--;) {
    double u=double(x)/GetWidth();
    for(WORD y=GetHeight(); y--;) {
      double v=double(y)/GetHeight();
      int Octaves=3;
      double Result=0;
      for(DWORD Frequency=1; Octaves--; Frequency<<=1) {
        Result+=Noise::Mosaic((u*10)*Frequency, (v*10)*Frequency, (0.5*10)*Frequency);
      }
      BYTE B=BYTE(Round(255*Clamped(0.0, Unsigned(Result)/3, 1.0)));
      SetPixel(x,y, RGB(B,B,B));
    }
  }
 

Clamped and Unsigned are declared in Global.h.

These are a few variations:

The noise functions return signed intervals in the range [-1,1] which are reasonably good to add together for mixing. It does mean that a fiddle-factor is needed to scale the amplitude (brightness) which is what the 'Clamped' and '/3' are doing to the Result.

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