SplitPathCoord: Ensure monotony and bounds for at

src/core/path_coord.cpp

@@ -383,12 +383,15 @@ SplitPathCoord SplitPathCoord::at(
         length_type length,
         const SplitPathCoord& first )
 {
-	auto& path_coords = *first.path_coords;
-	auto& coords = path_coords.coords();
-	auto& flags  = path_coords.flags();
+	const auto& path_coords = *first.path_coords;
+	const auto& coords = path_coords.coords();
+	const auto& flags  = path_coords.flags();
 
 	SplitPathCoord split = first;
-	split.path_coord_index = path_coords.upperBound(length, first.path_coord_index, first.path_coords->size()-1);
+	if (length > first.clen)
+	{
+		split.path_coord_index = path_coords.upperBound(length, first.path_coord_index, first.path_coords->size()-1);
+	}
 	if (split.path_coord_index > first.path_coord_index)
 	{
 		// New path coordinate, really
@@ -403,10 +406,12 @@ SplitPathCoord SplitPathCoord::at(
 
 		auto factor = 1.0f;
 		if (qFuzzyCompare(1.0f + length, 1.0f + current_coord.clen) ||
-		    qFuzzyCompare(1.0f + curve_length, 1.0f))
+		    qFuzzyCompare(1.0f + curve_length, 1.0f) ||
+		    length > current_coord.clen)
 		{
 			// Close match at current path coordinate,
-			// or near-zero curve length.
+			// or near-zero curve length,
+			// or length exceeding path length.
 			split.pos   = current_coord.pos;
 			split.clen  = current_coord.clen;
 			split.param = current_coord.param;
@@ -506,9 +511,10 @@ SplitPathCoord SplitPathCoord::at(
 		{
 			--split.path_coord_index;
 		}
+
+		split.index = path_coords[split.path_coord_index].index;
 	}
 
-	split.index = path_coords[split.path_coord_index].index;
 	return split;
 }
 

test/path_object_t.cpp

@@ -20,6 +20,9 @@
 
 #include "path_object_t.h"
 
+#include <iterator>
+
+#include <Qt>
 #include <QtTest>
 
 #include "core/map.h"
@@ -1206,6 +1209,83 @@ void PathObjectTest::recalculatePartsTest()
 	}
 }
 
+void PathObjectTest::splitPathCoordAtTest()
+{
+	const PathCoord::length_type lengths_to_check[] = {
+		-0.2f, 0.2f, 1.0f, 1.2f, 1.4f, 1.5f, 1.8, 2.0f, 2.2f, 3.2f, 5.0f
+	};
+	using std::begin; using std::end;
+	{
+		// Square, straight, closed
+		const MapCoordVector coords = {
+		    { 0.0, 0.0 }, { 1.0, 0.0 }, { 1.0, 1.0 }, { 0.0, 1.0 }, { 0.0, 0.0, MapCoord::HolePoint }
+		};
+
+		PathCoordVector path_coords { coords };
+		path_coords.update(0);
+		QCOMPARE(path_coords.size(), std::size_t(5));
+
+		const auto max_clen = path_coords.back().clen;
+		QCOMPARE(max_clen, 4.0f);
+
+		const auto split = SplitPathCoord::at(1.5f, SplitPathCoord::begin(path_coords));
+		{
+			const auto& prev = path_coords[split.path_coord_index];
+			QCOMPARE(prev.clen, 1.0f);
+			const auto& next = path_coords[split.path_coord_index + 1];
+			QCOMPARE(next.clen, 2.0f);
+		}
+
+		auto prev_clen = SplitPathCoord::at(lengths_to_check[0], split).clen;
+		for (auto it = begin(lengths_to_check)+1, last = end(lengths_to_check); it != last; ++it)
+		{
+			const auto requested_clen = *it;
+			const auto clen = SplitPathCoord::at(requested_clen, split).clen;
+			QVERIFY(clen >= prev_clen);          // monotone
+			if (requested_clen >= max_clen)
+				QCOMPARE(clen, max_clen);        // upper bound			
+			else if (requested_clen >= split.clen)
+				QCOMPARE(clen, requested_clen);  // expected case
+			prev_clen = clen;
+		}
+	}
+
+	{
+		// Line, curved
+		const MapCoordVector coords = {
+		    { 0.0, 0.0, MapCoord::CurveStart }, { 1.0, 0.0 }, { 1.0, 1.0 }, { 0.0, 1.0, MapCoord::HolePoint }
+		};
+
+		PathCoordVector path_coords { coords };
+		path_coords.update(0);
+		QCOMPARE(path_coords.size(), std::size_t(10));
+
+		const auto max_clen = path_coords.back().clen;
+		QCOMPARE(max_clen, 2.00034f);
+
+		const auto split = SplitPathCoord::at(1.5f, SplitPathCoord::begin(path_coords));
+		{
+			const auto& prev = path_coords[split.path_coord_index];
+			QCOMPARE(prev.clen, 1.29314f);
+			const auto& next = path_coords[split.path_coord_index + 1];
+			QCOMPARE(next.clen, 1.52751f);
+		}
+
+		auto prev_clen = SplitPathCoord::at(lengths_to_check[0], split).clen;
+		for (auto it = begin(lengths_to_check)+1, last = end(lengths_to_check); it != last; ++it)
+		{
+			const auto requested_clen = *it;
+			const auto clen = SplitPathCoord::at(requested_clen, split).clen;
+			QVERIFY(clen >= prev_clen);          // monotone
+			if (requested_clen >= max_clen)
+				QCOMPARE(clen, max_clen);        // upper bound
+			else if (requested_clen >= split.clen)
+				QCOMPARE(clen, requested_clen);  // expected case
+			prev_clen = clen;
+		}
+	}
+}
+
 
 
 /*

test/path_object_t.h

@@ -78,6 +78,9 @@ private slots:
 	/** Tests recalculation of path parts from input coords. */
 	void recalculatePartsTest();
 	void recalculatePartsTest_data();
+
+	/** Test SplitPathCoord.at stability. */
+	void splitPathCoordAtTest();
 };
 
 #endif