for (iter.x = begin.x; iter.x < end.x; ++iter.x) {
if (index->IsBorder(iter)) continue;
Chunk *light_chunk = index->Get(iter);
for (iter.x = begin.x; iter.x < end.x; ++iter.x) {
if (index->IsBorder(iter)) continue;
Chunk *light_chunk = index->Get(iter);