Method renderFallbackTile

app/src/UI/Widgets/GPS.cpp:674–713

* @brief Renders a scaled ancestor tile when the target tile is not yet cached. */

 * @brief Renders a scaled ancestor tile when the target tile is not yet cached.
 */
bool Widgets::GPS::renderFallbackTile(
  QPainter* painter, int tx, int ty, int baseZoom, const QRect& targetRect, double scaledTileSize)
{
  const int tileSize = 256;
  for (int z = baseZoom - 1; z >= MIN_ZOOM; --z) {
    const int dz              = baseZoom - z;
    const int tileScale       = 1 << dz;
    const int parentTx        = tx >> dz;
    const int parentTy        = ty >> dz;
    const int wrappedParentTx = (parentTx % (1 << z) + (1 << z)) % (1 << z);
    const QString parentUrl   = tileUrl(wrappedParentTx, parentTy, z);

    if (!s_tileCache.contains(parentUrl))
      continue;

    auto* src = s_tileCache.object(parentUrl);
    const QRect sourceRect((tx % tileScale) * (tileSize / tileScale),
                           (ty % tileScale) * (tileSize / tileScale),
                           tileSize / tileScale,
                           tileSize / tileScale);

    const auto cropped    = src->copy(sourceRect);
    const int roundedSize = qRound(scaledTileSize);

    QImage finalTile;
    if (qAbs(baseZoom - z) > 5) {
      QImage img = cropped.scaled(1, 1, Qt::IgnoreAspectRatio, Qt::FastTransformation);
      finalTile  = QImage(roundedSize, roundedSize, QImage::Format_ARGB32);
      finalTile.fill(img.pixelColor(0, 0));
    } else {
      finalTile =
        cropped.scaled(roundedSize, roundedSize, Qt::KeepAspectRatio, Qt::SmoothTransformation);
    }

    painter->drawImage(targetRect, finalTile);
    return true;
  }

  return false;
}

/**
 * @brief Draws the NASA GIBS weather overlay tile if available in the cache.