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From: Mike Day 
Sent: Wednesday, January 31, 2007 6:52 AM
To: tech
Subject: curiously small code...

I tried swizzling my test texture and mipmaps and was surprised how little code was needed to do it. The following is paraphrasing somewhat, but should work given a suitable definition and operators for the ‘texel’ type. It swizzles a square texture with ‘size’ texels and then generates all the mip levels down to 1x1:


  // swizzle base texture
  texel *u=unswizzled, *s=swizzled;
  for (u32 y=0; y<size; y=((y|0x5555555)+1)&0xAAAAAAA)
  {
    for (u32 x=0; x<size; x=((x|0xAAAAAAA)+1)&0x5555555)
    {
      s[x|y] = *u++;
    }
  }

  // generate swizzled mip maps
  for (texel *m=s+size; s<m-1; s+=4, m++)
  {
    *m = (s[0]+s[1]+s[2]+s[3])/4;
  }