прореживание сетки пикселей и сетки тайлов

matrix-rect-subsampling.cc

// Copyright (C) 2017, Aleksander A. Popov.

//
// Функции прореживания сетки пикселей и сетки тайлов
//

#include <QRect>

QRect subsample_erosion_twice(const QRect& rc) {
  return rc.isValid() ? QRect(QPoint(rc.left() / 2, rc.top() / 2),
                              QPoint(rc.right() == 0 ? -1 : rc.right() / 2,
                                     rc.bottom() == 0 ? -1 : rc.bottom() / 2))
                      : rc;
}

int sign(int v) {
  return v < 0 ? -1 : 1;
}

QRect subsample_dilation(const QRect& rc, int sx, int sy) {
  DCHECK_GE(sx, 1);
  DCHECK_GE(sy, 1);
  return rc.isValid()
             ? QRect(QPoint((rc.left() + sign(rc.left()) * (sx - 1)) / sx,
                            (rc.top() + sign(rc.top()) * (sy - 1)) / sy),
                     QPoint((rc.right() + sx - 1) / sx,
                            (rc.bottom() + sy - 1) / sy))
             : rc;
}

void generate_levels_rects(const QRect& pixels_rect_level0,
                           int sx,
                           int sy,
                           std::vector<QRect>* output_pixels_rects,
                           std::vector<QRect>* output_tiles_rects) {
  DCHECK(output_pixels_rects);
  DCHECK(output_tiles_rects);
  output_pixels_rects->clear();
  output_tiles_rects->clear();
  QRect pixels_rc = pixels_rect_level0;
  while (pixels_rc.isValid()) {
    output_pixels_rects->push_back(pixels_rc);
    output_tiles_rects->push_back(subsample_dilation(pixels_rc, sx, sy));
    pixels_rc = subsample_erosion_twice(pixels_rc);
  }
}