By George, I think she's got it!

earcut.cpp

@@ -17,35 +17,28 @@ drawvec reinforce(drawvec const &pts, std::vector<std::vector<Point>> polygon, d
 			size_t v2 = i + ((j + 1) % 3);
 			size_t v3 = i + ((j + 2) % 3);
 
-			double px, py;
-
-			if (distance_from_line(pts[indices[v1]].x, pts[indices[v1]].y,	// the point
-					       pts[indices[v2]].x, pts[indices[v2]].y,	// start of opposite side
-					       pts[indices[v3]].x, pts[indices[v3]].y,	// end of opposite side
-					       &px, &py) < 2 * scale) {
-				double ang = atan2(pts[indices[v1]].y - py, pts[indices[v1]].x - px);
-
-				// make a new triangle that is not so flat
-				out2.push_back(draw(VT_MOVETO, pts[indices[v2]].x, pts[indices[v2]].y));
-				out2.push_back(draw(VT_LINETO, pts[indices[v3]].x, pts[indices[v3]].y));
-				out2.push_back(draw(VT_LINETO, px + scale * 2 * cos(ang), py + scale * 2 * sin(ang)));
-				out2.push_back(draw(VT_LINETO, pts[indices[v2]].x, pts[indices[v2]].y));
-			}
-
 #if 0
-			long long dx = pts[indices[v2]].x - pts[indices[v1]].x;
+			out2.push_back(draw(VT_MOVETO, pts[indices[v1]].x, pts[indices[v1]].y));
-			long long dy = pts[indices[v2]].y - pts[indices[v1]].y;
+			out2.push_back(draw(VT_LINETO, pts[indices[v2]].x, pts[indices[v2]].y));
-			double d = sqrt(dx * dx + dy * dy);
+			out2.push_back(draw(VT_LINETO, pts[indices[v3]].x, pts[indices[v3]].y));
-			if (d < sqrt(2) * scale) {
+			out2.push_back(draw(VT_LINETO, pts[indices[v1]].x, pts[indices[v1]].y));
-				// make a new triangle with a longer side
-				double ang = atan2(dy, dx);
-
-				out2.push_back(draw(VT_MOVETO, pts[indices[v3]].x, pts[indices[v3]].y));
-				out2.push_back(draw(VT_LINETO, pts[indices[v1]].x - sqrt(2) * scale * cos(ang), pts[indices[v1]].y - sqrt(2) * scale * sin(ang)));
-				out2.push_back(draw(VT_LINETO, pts[indices[v2]].x + sqrt(2) * scale * cos(ang), pts[indices[v2]].y + sqrt(2) * scale * sin(ang)));
-				out2.push_back(draw(VT_LINETO, pts[indices[v3]].x, pts[indices[v3]].y));
-			}
 #endif
+
+			double px, py;
+			double d = distance_from_line_noclamp(pts[indices[v1]].x, pts[indices[v1]].y,
+							      pts[indices[v2]].x, pts[indices[v2]].y,
+							      pts[indices[v3]].x, pts[indices[v3]].y,
+							      &px, &py);
+
+			if (d < scale) {
+				double ang = atan2(py - pts[indices[v1]].y, px - pts[indices[v1]].x);
+				double dist = scale - d;
+
+				out2.push_back(draw(VT_MOVETO, pts[indices[v1]].x, pts[indices[v1]].y));
+				out2.push_back(draw(VT_LINETO, pts[indices[v2]].x + dist * cos(ang), pts[indices[v2]].y + dist * sin(ang)));
+				out2.push_back(draw(VT_LINETO, pts[indices[v3]].x + dist * cos(ang), pts[indices[v3]].y + dist * sin(ang)));
+				out2.push_back(draw(VT_LINETO, pts[indices[v1]].x, pts[indices[v1]].y));
+			}
 		}
 	}
 
@@ -95,6 +88,7 @@ drawvec fix_by_triangulation(drawvec const &dv, int z, int detail) {
 	for (auto const &d : additional) {
 		out2.push_back(d);
 	}
+
 	for (auto const &d : dv) {
 		out2.push_back(d);
 	}

geometry.cpp

@@ -380,6 +380,29 @@ double distance_from_line(long long point_x, long long point_y, long long segA_x
 	return out;
 }
 
+double distance_from_line_noclamp(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y, double *px, double *py) {
+	long long p2x = segB_x - segA_x;
+	long long p2y = segB_y - segA_y;
+	double something = p2x * p2x + p2y * p2y;
+	double u = (0 == something) ? 0 : ((point_x - segA_x) * p2x + (point_y - segA_y) * p2y) / (something);
+
+	double x = segA_x + u * p2x;
+	double y = segA_y + u * p2y;
+
+	if (px != NULL) {
+		*px = std::round(x);
+	}
+	if (py != NULL) {
+		*py = std::round(y);
+	}
+
+	double dx = x - point_x;
+	double dy = y - point_y;
+
+	double out = std::round(sqrt(dx * dx + dy * dy) * 16.0) / 16.0;
+	return out;
+}
+
 // https://github.com/Project-OSRM/osrm-backend/blob/733d1384a40f/Algorithms/DouglasePeucker.cpp
 static void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, size_t retain) {
 	std::stack<int> recursion_stack;

geometry.hpp

@@ -97,6 +97,7 @@ drawvec clip_point(drawvec &geom, long long x1, long long y1, long long x2, long
 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, double *px, double *py);
+double distance_from_line_noclamp(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y, double *px, double *py);
 
 std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int ny,
 		     int detail, int buffer, std::set<std::string> const &keep, bool do_compress,

tile.cpp

@@ -614,11 +614,16 @@ void *partial_feature_worker(void *v) {
 		drawvec geom = (*partials)[i].geoms[0];
 
 		if (t == VT_POLYGON) {
+			geom = remove_noop(geom, VT_POLYGON, 0);
 			drawvec cleaned = clean_or_clip_poly(geom, 0, 0, false, false);
-			drawvec fixed = fix_by_triangulation(geom, z, out_detail);
+			drawvec fixed = fix_by_triangulation(cleaned, z, out_detail);
+			geom = clean_or_clip_poly(fixed, 0, 0, false, false);
+#if 0
 			if (fixed != cleaned) {
 				geom = fixed;
 			}
+			(*partials)[i].t = t = VT_LINE;
+#endif
 		}
 
 		to_tile_scale(geom, z, out_detail);