From 33052aa60bedeb0d049fcf9bf856765bfb851859 Mon Sep 17 00:00:00 2001
From: Erica Fischer <enf@felt.com>
Date: Tue, 14 Nov 2023 18:00:03 -0800
Subject: [PATCH] Make polygon scaling its own function

---
 polygon.cpp | 17 ++++++++++-------
 polygon.hpp |  3 ++-
 tile.cpp    | 28 ++--------------------------
 3 files changed, 14 insertions(+), 34 deletions(-)

diff --git a/polygon.cpp b/polygon.cpp
index 4515539d..7b323455 100644
--- a/polygon.cpp
+++ b/polygon.cpp
@@ -40,7 +40,12 @@ struct point {
 
 typedef std::pair<point, point> segment;
 
-bool visible(segment const &seg, long long extent) {
+bool spindle_visible(segment const &seg, long long extent) {
+	if (extent == 0) {
+		// extent of 0 means no spindle revival
+		return false;
+	}
+
 	long long minx = std::min(seg.first.x, seg.second.x);
 	long long miny = std::min(seg.first.y, seg.second.y);
 	long long maxx = std::max(seg.first.x, seg.second.x);
@@ -77,7 +82,7 @@ bool fix_opposites(std::vector<segment> &segs, std::set<segment> &affected, long
 			long long dx = segs[i].second.x - segs[i].first.x;
 			long long dy = segs[i].second.y - segs[i].first.y;
 			long long dsq = dx * dx + dy * dy;
-			if (visible(segs[i], extent) && dsq >= 5 * 5) {
+			if (spindle_visible(segs[i], extent) && dsq >= 5 * 5) {
 				// alter the segment instead to keep it from collapsing away
 
 				double ang = atan2(dy, dx) - M_PI / 2;
@@ -694,7 +699,7 @@ double triangle_area(drawvec const &geom, size_t base, size_t increment, size_t
 	return area;
 }
 
-drawvec scale_poly(drawvec const &geom, int z, int detail) {
+drawvec scale_polygon(drawvec const &geom, int z, int detail) {
 	double scale = 1LL << (32 - detail - z);
 	drawvec out;
 
@@ -762,9 +767,7 @@ drawvec scale_poly(drawvec const &geom, int z, int detail) {
 	return out;
 }
 
-drawvec clean_polygon(drawvec geom, int z, int detail) {
-	geom = scale_poly(geom, z, detail);
-
+drawvec clean_polygon(drawvec geom, long long extent) {
 	// decompose polygon rings into segments
 
 	std::vector<std::pair<point, point>> segments;
@@ -796,7 +799,7 @@ drawvec clean_polygon(drawvec geom, int z, int detail) {
 
 	// snap-round intersecting segments
 
-	snap_round(segments, 1LL << detail);
+	snap_round(segments, extent);
 
 	// reassemble segments into rings
 
diff --git a/polygon.hpp b/polygon.hpp
index 1f23d3cf..dcb8f490 100644
--- a/polygon.hpp
+++ b/polygon.hpp
@@ -1 +1,2 @@
-drawvec clean_polygon(drawvec geom, int z, int detail);
+drawvec clean_polygon(drawvec geom, long long extent);
+drawvec scale_polygon(drawvec const &geom, int z, int detail);
diff --git a/tile.cpp b/tile.cpp
index b4e62c76..82f360c3 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -615,36 +615,12 @@ void *partial_feature_worker(void *v) {
 		drawvec geom = (*partials)[i].geoms[0];
 
 		if (t == VT_POLYGON) {
-			geom = clean_polygon(geom, z, out_detail);
-			// (*partials)[i].t = t = VT_LINE;
+			geom = scale_polygon(geom, z, out_detail);
+			geom = clean_polygon(geom, 1LL << out_detail);
 		} else {
 			to_tile_scale(geom, z, out_detail);
 		}
 
-#if 0
-		if (t == VT_POLYGON) {
-			// Scaling may have made the polygon degenerate.
-			// Give Clipper a chance to try to fix it.
-			{
-				drawvec before = geom;
-				// we can try scaling up because this is now tile scale
-				geom = clean_or_clip_poly(geom, 0, 0, false, true);
-				if (additional[A_DEBUG_POLYGON]) {
-					check_polygon(geom);
-				}
-
-				if (geom.size() < 3) {
-					if (area > 0) {
-						// area is in world coordinates, calculated before scaling down
-						geom = revive_polygon(before, area, z, out_detail);
-					} else {
-						geom.clear();
-					}
-				}
-			}
-		}
-#endif
-
 		if (t == VT_POLYGON && additional[A_GENERATE_POLYGON_LABEL_POINTS]) {
 			t = (*partials)[i].t = VT_POINT;
 			geom = checkerboard_anchors(from_tile_scale(geom, z, out_detail), (*partials)[i].tx, (*partials)[i].ty, z, (*partials)[i].label_point);