svoid test_QuadTreeBitMatrix() {

  // 4*4, one pixel white

  BitSetMatrix m = new(4, 4);

  m.set(1, 1);

  QuadTreeBitMatrix qt = bitMatrixToQuadTree(m);

  assertTrueVerbose(equal := eqMatrices(m, qt));

  assertEqualsVerbose(2, qt.compositeNodeCount());

  // turn pixel back to black

  qt.set(1, 1, false);

  m.set(1, 1, false);

  assertTrueVerbose(equal := eqMatrices(m, qt));

  print(structure(qt));

  qt.set(1, 1, false);

  print(structure(qt));

  assertEqualsVerbose(0, qt.compositeNodeCount());

  // all pixels white

  for y to 4:

    for x to 4:

      qt.set(x, y);

  assertEqualsVerbose(0, qt.compositeNodeCount());

  test_QuadTreeBitMatrix_2();

}

svoid test_QuadTreeBitMatrix_2() {

  for (double p = .1; p < 1; p += .1) {

    new Average nodes;

    repeat 100 {

      var matrix = randomBitMatrix(8, 8, p);

      QuadTreeBitMatrix qt = bitMatrixToQuadTree(matrix);

      nodes.add(qt.compositeNodeCount());

      assertTrue(eqMatrices(matrix, qt));

    }

    printVars(+p, +nodes);

  }

}