From f380b20ddf1ead6447a6ee6e137a14c4aa226c12 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sat, 23 Mar 2024 21:41:10 +0000
Subject: Handle and test concave surface boundaries

---
 game/geoData.cpp                    | 19 ++++++++++++-----
 test/fixtures/geoData/deform/1.json | 41 +++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/game/geoData.cpp b/game/geoData.cpp
index 80a4eba..30c382c 100644
--- a/game/geoData.cpp
+++ b/game/geoData.cpp
@@ -446,11 +446,20 @@ GeoData::setHeights(const std::span<const GlobalPosition3D> triangleStrip)
 					return extrusionDir;
 				};
 				// Previous half edge end to current half end start arc tangents
-				const Arc arc {e0, e1};
-				const auto limit = std::ceil(arc.length() * 5.F / pi);
-				const auto inc = arc.length() / limit;
-				for (float step = 0; step <= limit; step += 1.F) {
-					const auto direction = sincosf(arc.first + (step * inc));
+				if (const Arc arc {e0, e1}; arc.length() < pi) {
+					const auto limit = std::ceil(arc.length() * 5.F / pi);
+					const auto inc = arc.length() / limit;
+					for (float step = 0; step <= limit; step += 1.F) {
+						const auto direction = sincosf(arc.first + (step * inc));
+						VertexHandle extrusionVertex;
+						extrusionExtents.emplace_back(boundaryVertex, extrusionVertex,
+								doExtrusion(extrusionVertex, direction, p1, -MAX_SLOPE),
+								doExtrusion(extrusionVertex, direction, p1, MAX_SLOPE));
+						assert(extrusionVertex.is_valid());
+					}
+				}
+				else {
+					const auto direction = normalize(e0 + e1) / sinf((arc.length() - pi) / 2.F);
 					VertexHandle extrusionVertex;
 					extrusionExtents.emplace_back(boundaryVertex, extrusionVertex,
 							doExtrusion(extrusionVertex, direction, p1, -MAX_SLOPE),
diff --git a/test/fixtures/geoData/deform/1.json b/test/fixtures/geoData/deform/1.json
index fb45ce4..6930238 100644
--- a/test/fixtures/geoData/deform/1.json
+++ b/test/fixtures/geoData/deform/1.json
@@ -156,5 +156,46 @@
 				"/tmp/geoData5.tga"
 			]
 		]
+	],
+	[
+		[
+			[
+				1500,
+				2000,
+				800
+			],
+			[
+				3000,
+				2000,
+				800
+			],
+			[
+				5000,
+				4000,
+				800
+			],
+			[
+				3500,
+				700,
+				800
+			]
+		],
+		[
+			[
+				[
+					[
+						-1000,
+						-3000,
+						7000
+					],
+					[
+						1,
+						1,
+						-1.5
+					]
+				],
+				"/tmp/geoData6.tga"
+			]
+		]
 	]
 ]
-- 
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