infinite heightmap tricks

//  hmap.halfww    is    world width / 2
//  hmap.ww        is    world width

// get the wrapped coordinates  relative to   ax, az  (and store them in wp)
void setWrapPos(float ax,  float az,
                float bx, float by, float bz,
                gamex::xVec3f & wp)
{
  wp.x = bx; wp.z = bz; wp.y = by;

  if ( (bx - ax) > hmap.halfww ) { wp.x -= hmap.ww;}
  else if ( (bx - ax) < -hmap.halfww ) { wp.x += hmap.ww;}

  if ( (bz - az) > hmap.halfwh ) { wp.z -= hmap.wh;}
  else if ( (bz - az) < -hmap.halfwh ) { wp.z += hmap.wh;}

}//setwrappos


//check if the coordinates need to be wrapped around
void checkWrapPos(float & ax, float & az)
{
 if (ax < 0.0f )    { ax += hmap.ww; }
 else if (ax > hmap.ww ) { ax -= hmap.ww; }
 if (az < 0.0f )    { az += hmap.wh; }
 else if (az > hmap.wh ) { az -= hmap.wh; }

}//checkwrap


// mw   is terrain  width in number of vertices
// needs to be power of 2 ( 2, 4, 8, 16, 32 ..  256  etc)  for bitwise-AND  trick to work

float
xHeightMap::getHeightAt(int ax, int az)
{
  ax &= (mw-1); //32 mw  -> 31
  az &= (mh-1);
  return vecHeight[ax+(az*mw)];
}//getheightat

void
xHeightMap::setHeightAt(int ax, int az, float h)
{
  ax &= (mw-1); //32 mw  -> 31
  az &= (mh-1);
  vecHeight[ax+(az*mw)] = h;
}//getheightat