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Shard the child tiles as widely as possible even if not skipping levels

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to help future parallelization
This commit is contained in:
Eric Fischer 2015-07-01 10:12:23 -07:00
parent b2fdcba6b0
commit af13a95dc1
1 changed files with 17 additions and 1 deletions
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18
tile.cc
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@ -365,7 +365,23 @@ void rewrite(drawvec &geom, int z, int nextzoom, int file_maxzoom, long long *bb
for (xo = 0; xo < span; xo++) {
for (yo = 0; yo < span; yo++) {
int j = xo * span + yo;
unsigned jx = tx * span + xo;
unsigned jy = ty * span + yo;
// j is the shard that the child tile's data is being written to.
//
// Be careful: We can't jump more zoom levels than MAX_ZOOM_INCREMENT
// because that could break the constraint that each of the children
// of the current tile must have its own shard, because the data for
// the child tile must be contiguous within the shard.
//
// But it's OK to spread children across all the shards, not just
// the four that would normally result from splitting one tile,
// because it will go through all the shards when it does the
// next zoom.
int j = ((jx & ((1 << MAX_ZOOM_INCREMENT) - 1)) << MAX_ZOOM_INCREMENT) |
((jy & ((1 << MAX_ZOOM_INCREMENT) - 1)));
long long bbox2[4];
int k;