From c7f3ad78f77094fe1b0321f64dc3934f00600612 Mon Sep 17 00:00:00 2001
From: Victor Giers <mail@victorgiers.com>
Date: Sat, 2 May 2026 04:13:56 +0200
Subject: [PATCH] Refactor: Improve type handling and robustness for foliage
 mask indices and keys in terrain brush stamps.

---
 src/viewport-three/viewport-host.ts | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/viewport-three/viewport-host.ts b/src/viewport-three/viewport-host.ts
index 23d3d683..612ee5f3 100644
--- a/src/viewport-three/viewport-host.ts
+++ b/src/viewport-three/viewport-host.ts
@@ -9685,10 +9685,14 @@ export class ViewportHost {
 
   private mergeTerrainBrushStampIndices(
     stroke: ActiveTerrainBrushStroke,
-    result: Pick<
-      ReturnType<typeof applyTerrainBrushStampInPlace>,
-      "heightSampleIndices" | "paintWeightIndices" | "foliageMaskValueIndices"
-    >
+    result: {
+      heightSampleIndices: readonly number[];
+      paintWeightIndices: readonly number[];
+      foliageMaskValueIndices?: ReturnType<
+        typeof applyTerrainBrushStampInPlace
+      >["foliageMaskValueIndices"];
+      foliageMaskValueKeys?: readonly string[];
+    }
   ) {
     for (const sampleIndex of result.heightSampleIndices) {
       stroke.heightSampleIndices.add(sampleIndex);
@@ -9698,7 +9702,7 @@ export class ViewportHost {
       stroke.paintWeightIndices.add(paintWeightIndex);
     }
 
-    for (const foliageMaskValueIndex of result.foliageMaskValueIndices) {
+    for (const foliageMaskValueIndex of result.foliageMaskValueIndices ?? []) {
       stroke.foliageMaskValueKeys.add(
         createTerrainFoliageMaskValueKey(
           foliageMaskValueIndex.layerId,
@@ -9706,6 +9710,10 @@ export class ViewportHost {
         )
       );
     }
+
+    for (const foliageMaskValueKey of result.foliageMaskValueKeys ?? []) {
+      stroke.foliageMaskValueKeys.add(foliageMaskValueKey);
+    }
   }
 
   private beginTerrainBrushStroke(event: PointerEvent): boolean {