Function offsetPixel

tests/SphericalEffect.cpp:47–52

}

static QColor offsetPixel(std::shared_ptr<QImage> img, int dx, int dy) {
  const int cx = img->width() / 2 + dx;
  const int cy = img->height() / 2 + dy;
  return img->pixelColor(std::clamp(cx, 0, img->width() - 1),
                         std::clamp(cy, 0, img->height() - 1));
}

// Loose classifiers for our colored guide lines
static bool is_red(QColor c)    { return c.red()   >= 200 && c.green() <= 60 && c.blue() <= 60; }