/**
* Recursively find children of the given tile that are already loaded.
*
* @param id The tile ID that we should find children for.
* @param maxCoveringZoom The maximum zoom level of children to look for.
* @param retain An object that we add the found tiles to.
*
* @return boolean Whether the children found completely cover the tile.
*/
bool Source::findLoadedChildren(const Tile::ID& id, int32_t maxCoveringZoom, std::forward_list<Tile::ID>& retain) {
bool complete = true;
int32_t z = id.z;
auto ids = id.children(z + 1);
for (const Tile::ID& child_id : ids) {
const TileData::State state = hasTile(child_id);
if (state == TileData::State::parsed) {
retain.emplace_front(child_id);
} else {
complete = false;
if (z < maxCoveringZoom) {
// Go further down the hierarchy to find more unloaded children.
findLoadedChildren(child_id, maxCoveringZoom, retain);
}
}
}
return complete;
}
std::forward_list<mbgl::Tile::ID> Source::covering_tiles(const TransformState &state, int32_t clamped_zoom, const box& points) {
int32_t dim = std::pow(2, clamped_zoom);
std::forward_list<mbgl::Tile::ID> tiles;
bool is_raster = (info.type == SourceType::Raster);
double search_zoom = getZoom(state);
auto scanLine = [&tiles, clamped_zoom, is_raster, search_zoom](int32_t x0, int32_t x1, int32_t y, int32_t ymax) {
int32_t x;
if (y >= 0 && y <= ymax) {
for (x = x0; x < x1; x++) {
if (is_raster) {
Tile::ID id = Tile::ID(clamped_zoom, x, y);
auto ids = id.children(search_zoom);
for (const Tile::ID& child_id : ids) {
tiles.emplace_front(child_id.z, child_id.x, child_id.y);
}
} else {
tiles.emplace_front(clamped_zoom, x, y);
}
}
}
};
// Divide the screen up in two triangles and scan each of them:
// \---+
// | \ |
// +---\.
_scanTriangle(points.tl, points.tr, points.br, 0, dim, scanLine);
_scanTriangle(points.br, points.bl, points.tl, 0, dim, scanLine);
const vec2<double>& center = points.center;
tiles.sort([¢er](const Tile::ID& a, const Tile::ID& b) {
// Sorts by distance from the box center
return std::fabs(a.x - center.x) + std::fabs(a.y - center.y) <
std::fabs(b.x - center.x) + std::fabs(b.y - center.y);
});
tiles.unique();
return tiles;
}