From 883ece290a5274953a3d6a0b9d6e229c26327e03 Mon Sep 17 00:00:00 2001
From: Paul Elliott <paul.elliott@kitware.com>
Date: Fri, 5 Jul 2024 12:26:00 -0400
Subject: [PATCH] fix(polygon): merge overlapping polygons better

---
 src/store/tools/polygons.ts | 40 +++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/store/tools/polygons.ts b/src/store/tools/polygons.ts
index 3decc880..f25ecc97 100644
--- a/src/store/tools/polygons.ts
+++ b/src/store/tools/polygons.ts
@@ -1,5 +1,5 @@
 import polybool, { Polygon } from '@velipso/polybool';
-import type { Vector3 } from '@kitware/vtk.js/types';
+import type { Vector3, Vector2 } from '@kitware/vtk.js/types';
 import { computed } from 'vue';
 import {
   ToolSelection,
@@ -64,7 +64,43 @@ export const usePolygonStore = defineAnnotationToolStore('polygon', () => {
     const firstTool = polygons[0];
     const { to3D } = getPlaneTransforms(firstTool.frameOfReference);
 
-    const points = unionPoly.regions[0].map(to3D);
+    // After union, regions will have shared points because we require overlap to union.
+    // Create one region/ring by splicing in the next region at the common point.
+    const pointEquals = (a: Vector2, b: Vector2) =>
+      a[0] === b[0] && a[1] === b[1];
+    const mergeRegions = (regions: Array<Array<Vector2>>) => {
+      const [mergedRegion, ...candidates] = regions;
+
+      while (candidates.length > 0) {
+        let regionIndex = 0;
+        let mergedCommonPointIndex = 0;
+        let candidateCommonPointIndex = 0;
+        for (let i = 0; i < candidates.length; i++) {
+          const candidate = candidates[i];
+          let candidatePointIndex = 0;
+          const commonPointIndex = mergedRegion.findIndex((point) =>
+            candidate.some((nextPoint, index) => {
+              candidatePointIndex = index;
+              return pointEquals(point, nextPoint);
+            })
+          );
+          if (commonPointIndex !== -1) {
+            regionIndex = i;
+            mergedCommonPointIndex = commonPointIndex;
+            candidateCommonPointIndex = candidatePointIndex;
+            break;
+          }
+        }
+        const [toMerge] = candidates.splice(regionIndex, 1);
+        const oldStart = toMerge.splice(0, candidateCommonPointIndex);
+        const startWithCommonPoint = [...toMerge, ...oldStart];
+        mergedRegion.splice(mergedCommonPointIndex, 0, ...startWithCommonPoint);
+      }
+
+      return mergedRegion;
+    };
+
+    const points = mergeRegions(unionPoly.regions).map(to3D);
 
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     const { id: _, ...toolProps } = polygons[0];