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Clean up the gamma semantics a little.

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0 (default) means unchanged: maxzoom contains all the dots.

Positive number, even very small, means that it still checks
the gap size and thins out dots if they are close together.

Negative number means no gamma, and the old random instead of
uniform dropping at low zooms.
This commit is contained in:
Eric Fischer
2015-03-23 14:44:21 -07:00
parent 26bcdef06b
commit a880f44a91
3 changed files with 29 additions and 27 deletions
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tile.cc
+27 -25
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@@ -489,11 +489,11 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
continue;
}
if (t == VT_POINT && z < feature_minzoom && gamma == 0) {
if (t == VT_POINT && z < feature_minzoom && gamma < 0) {
continue;
}
if (t == VT_POINT && gamma != 0) {
if (t == VT_POINT && gamma >= 0) {
seq++;
if (seq >= 0) {
seq -= interval;
@@ -501,32 +501,34 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
continue;
}
unsigned long long index = encode(bbox[0] / 2 + bbox[2] / 2, bbox[1] / 2 + bbox[3] / 2);
if (gap > 0) {
if (index == previndex) {
continue; // Exact duplicate: can't fulfil the gap requirement
if (gamma > 0) {
unsigned long long index = encode(bbox[0] / 2 + bbox[2] / 2, bbox[1] / 2 + bbox[3] / 2);
if (gap > 0) {
if (index == previndex) {
continue; // Exact duplicate: can't fulfil the gap requirement
}
if (exp(log((index - previndex) / scale) * gamma) >= gap) {
// Dot is further from the previous than the nth root of the gap,
// so produce it, and choose a new gap at the next point.
gap = 0;
} else {
continue;
}
} else {
gap = (index - previndex) / scale;
if (gap == 0) {
continue; // Exact duplicate: skip
} else if (gap < 1) {
continue; // Narrow dot spacing: need to stretch out
} else {
gap = 0; // Wider spacing than minimum: so pass through unchanged
}
}
if (exp(log((index - previndex) / scale) * gamma) >= gap) {
// Dot is further from the previous than the nth root of the gap,
// so produce it, and choose a new gap at the next point.
gap = 0;
} else {
continue;
}
} else {
gap = (index - previndex) / scale;
if (gap == 0) {
continue; // Exact duplicate: skip
} else if (gap < 1) {
continue; // Narrow dot spacing: need to stretch out
} else {
gap = 0; // Wider spacing than minimum: so pass through unchanged
}
previndex = index;
}
previndex = index;
}
bool reduced = false;