From ca3736b3a896557536c0aa4c0cee1f156e118b54 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 1 Jan 2025 12:53:43 +0000
Subject: Walk terrain along a curve - edge cases exist

---
 game/geoData.cpp | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

(limited to 'game/geoData.cpp')

diff --git a/game/geoData.cpp b/game/geoData.cpp
index ce88e5b..37abc4c 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -289,6 +289,50 @@ GeoData::walkUntil(const PointFace & from, const GlobalPosition2D to, Tester<Wal
 	}
 }
 
+void
+GeoData::walk(const PointFace & from, GlobalPosition2D to, GlobalPosition2D centre, Consumer<WalkStep> op) const
+{
+	walkUntil(from, to, centre, [&op](const auto & fh) {
+		op(fh);
+		return false;
+	});
+}
+
+void
+GeoData::walkUntil(const PointFace & from, GlobalPosition2D to, GlobalPosition2D centre, Tester<WalkStep> op) const
+{
+	WalkStep step {
+			.current = from.face(this),
+	};
+	if (!step.current.is_valid()) {
+		const auto entryEdge = findEntry(from.point, to);
+		if (!entryEdge.is_valid()) {
+			return;
+		}
+		step.current = opposite_face_handle(entryEdge);
+	}
+	ArcSegment arc {centre, from.point, to};
+	while (step.current.is_valid() && !op(step)) {
+		step.previous = step.current;
+		for (const auto next : fh_range(step.current)) {
+			if (opposite_halfedge_handle(next) == step.exitHalfedge) {
+				continue;
+			}
+			step.current = opposite_face_handle(next);
+			if (step.current.is_valid()) {
+				const auto e1 = point(to_vertex_handle(next));
+				const auto e2 = point(to_vertex_handle(opposite_halfedge_handle(next)));
+				if (const auto intersect = arc.crossesLineAt(e1, e2)) {
+					step.exitHalfedge = next;
+					step.exitPosition = intersect.value();
+					break;
+				}
+			}
+			step.current.reset();
+		}
+	}
+}
+
 void
 GeoData::boundaryWalk(Consumer<HalfedgeHandle> op) const
 {
-- 
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