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

geometry.hpp

@@ -65,11 +65,10 @@ void to_tile_scale(drawvec &geom, int z, int detail);
 drawvec from_tile_scale(drawvec const &geom, int z, int detail);
 drawvec remove_noop(drawvec geom, int type, int shift);
 drawvec clip_point(drawvec &geom, int z, long long buffer);
-drawvec clean_or_clip_poly(drawvec &geom, int z, int buffer, bool clip);
-drawvec simple_clip_poly(drawvec &geom, int z, int buffer);
+drawvec clean_or_clip_poly(drawvec &geom, int z, int buffer, bool clip, bool try_scaling);
 drawvec close_poly(drawvec &geom);
 drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *still_needs_simplification, bool *reduced_away, double *accum_area, serial_feature *this_feature, serial_feature *tiny_feature);
-int clip(double *x0, double *y0, double *x1, double *y1, double xmin, double ymin, double xmax, double ymax);
+int clip(long long *x0, long long *y0, long long *x1, long long *y1, long long xmin, long long ymin, long long xmax, long long ymax);
 drawvec clip_lines(drawvec &geom, int z, long long buffer);
 drawvec stairstep(drawvec &geom, int z, int detail);
 bool point_within_tile(long long x, long long y, int z);
@@ -84,11 +83,15 @@ double get_mp_area(drawvec &geom);
 drawvec polygon_to_anchor(const drawvec &geom);
 drawvec checkerboard_anchors(drawvec const &geom, int tx, int ty, int z, unsigned long long label_point);
 
-drawvec simple_clip_poly(drawvec &geom, long long x1, long long y1, long long x2, long long y2);
+drawvec simple_clip_poly(drawvec &geom, int z, int buffer, drawvec &shared_nodes, bool prevent_simplify_shared_nodes);
+drawvec simple_clip_poly(drawvec &geom, long long x1, long long y1, long long x2, long long y2, bool prevent_simplify_shared_nodes);
+drawvec simple_clip_poly(drawvec &geom, long long x1, long long y1, long long x2, long long y2,
+			 long long ax, long long ay, long long bx, long long by, drawvec &shared_nodes, bool prevent_simplify_shared_nodes);
 drawvec clip_lines(drawvec &geom, long long x1, long long y1, long long x2, long long y2);
 drawvec clip_point(drawvec &geom, long long x1, long long y1, long long x2, long long y2);
 void visvalingam(drawvec &ls, size_t start, size_t end, double threshold, size_t retain);
 int pnpoly(const drawvec &vert, size_t start, size_t nvert, long long testx, long long testy);
+double distance_from_line(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y);
 
 std::string overzoom(std::string s, int oz, int ox, int oy, int nz, int nx, int ny,
 		     int detail, int buffer, std::set<std::string> const &keep);