From 4d7694e1f5266d2733b8b2674e79ec0d683d2ea4 Mon Sep 17 00:00:00 2001
From: Victor Giers <mail@victorgiers.com>
Date: Wed, 13 May 2026 14:19:13 +0200
Subject: [PATCH] auto-git:  [add]
 src/viewport-three/terrain-grid-resize-controls.ts

---
 .../terrain-grid-resize-controls.ts           | 87 +++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 src/viewport-three/terrain-grid-resize-controls.ts

diff --git a/src/viewport-three/terrain-grid-resize-controls.ts b/src/viewport-three/terrain-grid-resize-controls.ts
new file mode 100644
index 00000000..e63bdfbb
--- /dev/null
+++ b/src/viewport-three/terrain-grid-resize-controls.ts
@@ -0,0 +1,87 @@
+import {
+  getTerrainFootprintDepth,
+  getTerrainFootprintWidth,
+  MIN_TERRAIN_SAMPLE_COUNT,
+  resizeTerrainGrid,
+  type Terrain,
+  type TerrainGridResizeDirectionX,
+  type TerrainGridResizeDirectionZ
+} from "../document/terrains";
+
+export type TerrainGridResizeSide = "east" | "west" | "north" | "south";
+
+export interface TerrainGridResizeDirections {
+  resizeDirectionX?: TerrainGridResizeDirectionX;
+  resizeDirectionZ?: TerrainGridResizeDirectionZ;
+}
+
+export function getTerrainGridResizeDirectionsForSide(
+  side: TerrainGridResizeSide
+): TerrainGridResizeDirections {
+  switch (side) {
+    case "east":
+      return { resizeDirectionX: "east" };
+    case "west":
+      return { resizeDirectionX: "west" };
+    case "north":
+      return { resizeDirectionZ: "north" };
+    case "south":
+      return { resizeDirectionZ: "south" };
+  }
+}
+
+export function resolveTerrainGridResizeSideFromLocalPosition(
+  terrain: Terrain,
+  localX: number,
+  localZ: number,
+  threshold: number
+): TerrainGridResizeSide | null {
+  const width = getTerrainFootprintWidth(terrain);
+  const depth = getTerrainFootprintDepth(terrain);
+
+  if (
+    localX < 0 ||
+    localX > width ||
+    localZ < 0 ||
+    localZ > depth ||
+    threshold <= 0
+  ) {
+    return null;
+  }
+
+  const candidates: Array<{ side: TerrainGridResizeSide; distance: number }> = [
+    { side: "west", distance: localX },
+    { side: "east", distance: width - localX },
+    { side: "south", distance: localZ },
+    { side: "north", distance: depth - localZ }
+  ].filter((candidate) => candidate.distance <= threshold);
+
+  if (candidates.length === 0) {
+    return null;
+  }
+
+  candidates.sort((left, right) => left.distance - right.distance);
+  return candidates[0]?.side ?? null;
+}
+
+export function resizeTerrainGridFromBorderDrag(
+  terrain: Terrain,
+  side: TerrainGridResizeSide,
+  outwardDragDistance: number
+): Terrain {
+  const sampleDelta = Math.round(outwardDragDistance / terrain.cellSize);
+  const directions = getTerrainGridResizeDirectionsForSide(side);
+
+  return resizeTerrainGrid(terrain, {
+    sampleCountX:
+      side === "east" || side === "west"
+        ? Math.max(MIN_TERRAIN_SAMPLE_COUNT, terrain.sampleCountX + sampleDelta)
+        : terrain.sampleCountX,
+    sampleCountZ:
+      side === "north" || side === "south"
+        ? Math.max(MIN_TERRAIN_SAMPLE_COUNT, terrain.sampleCountZ + sampleDelta)
+        : terrain.sampleCountZ,
+    cellSize: terrain.cellSize,
+    ...directions
+  });
+}