Polygon shards (#105)

* Put all of this back in geometry.cpp for conflict resolution

* Stabilize line simplification to behave the same regardless of winding

* Round instead of truncating when clipping lines

* Restore non-Wagyu polygon clipping from prior to 2fdec7d2

* Make it round, not truncate, which reverts the last commit's test diffs

* Clip in floating point, not integers, which makes no difference

* Track nodes added at tile edges during clipping

* Scale geometry up before wagyu to prevent changes from precision loss

* Actually do the shared edge detection

* Fix cases where nodes were not being added at the tile boundary

* One more place I should have rounded

* Narrow down where the discrepancy comes in

* Revert "Narrow down where the discrepancy comes in"

This reverts commit 221c4c5fc0ac9a6567e091c6a94b3d87dc8ade83.

* Another attempt to narrow it down

* The discrepancy seems to be introduced in reordering. No obvious bug

* Was still truncating instead of rounding in projection

* Also makes no difference...

* Just forget that line reversal exists for a minute

* Just reversal no coalescing

* Try clipping in integers instead of floating point

* Don't simplify after coalescing if they said no simplification

* Check whether behavior is consistent with intentional simplification

* Replace more floating point with integer

* Are these three features enough to demonstrate the problem?

* Add a few more nearby borders

* All the features that touch tile 6/16/23

* Stay in integers in line simplification

* More attempts to solve failures to simplify consistently

* Fix most of the overflow errors

* Fix known cases of integer overflow

* All the tests change again

* Pull clipping and scaling code back out into clip.cpp

* Resolve the test conflicts

* Stabilize choice of which three points to keep with different windings

* Almost right, I think!

* Fix collapse of islands to shards

* Self-intersections in the same feature don't count

* Revert "Self-intersections in the same feature don't count"

This reverts commit e04b19916e.

* Don't scale down geometry if we are going to look for shared nodes

* Fix the missing multiply that was keeping simplification from happening

* Fix one more opportunity for overflow

* Somehow I deleted this test?

* Lost this test too

* Clean up debugging printfs

* Restore code sequence from main to make it reviewable

* Remove unneeded rounding

* Update documentation

* This test is no longer useful

* Back to floating point Douglas-Peucker to fix undersimplification

* Try an older ubuntu

* Revert "Try an older ubuntu"

This reverts commit 13fefacfd7.

* Log OS info

* Remove tests that are no longer needed

* Oops, did need that one after all

* Fix the arm vs x86 discrepancy?

* Try another quantization

* Cleanup from review

* Add a test for the actual purpose of this PR

projection.cpp

@@ -57,8 +57,8 @@ void lonlat2tile(double lon, double lat, int zoom, long long *x, long long *y) {
 	double lat_rad = lat * M_PI / 180;
 	unsigned long long n = 1LL << zoom;
 
-	long long llx = n * ((lon + 180) / 360);
-	long long lly = n * (1 - (log(tan(lat_rad) + 1 / cos(lat_rad)) / M_PI)) / 2;
+	long long llx = std::round(n * ((lon + 180) / 360));
+	long long lly = std::round(n * (1 - (log(tan(lat_rad) + 1 / cos(lat_rad)) / M_PI)) / 2);
 
 	*x = llx;
 	*y = lly;
@@ -84,8 +84,8 @@ void epsg3857totile(double ix, double iy, int zoom, long long *x, long long *y)
 		ix = 40000000.0;
 	}
 
-	*x = ix * (1LL << 31) / 6378137.0 / M_PI + (1LL << 31);
-	*y = ((1LL << 32) - 1) - (iy * (1LL << 31) / 6378137.0 / M_PI + (1LL << 31));
+	*x = std::round(ix * (1LL << 31) / 6378137.0 / M_PI + (1LL << 31));
+	*y = std::round(((1LL << 32) - 1) - (iy * (1LL << 31) / 6378137.0 / M_PI + (1LL << 31)));
 
 	if (zoom != 0) {
 		*x = std::round((double) *x / (1LL << (32 - zoom)));