feat: add terrain surface sampler

src/types/world/terrainSurface.ts

@@ -8,6 +8,18 @@ export type TerrainSurfaceKind =
 
 export type TerrainSurfaceRgb = readonly [number, number, number];
 
+export interface TerrainSurfaceUv {
+  u: number;
+  v: number;
+}
+
+export interface TerrainSurfaceBounds {
+  minX: number;
+  maxX: number;
+  minZ: number;
+  maxZ: number;
+}
+
 export interface TerrainSurfaceColorConfig {
   hex: string;
   rgb: TerrainSurfaceRgb;
@@ -16,3 +28,9 @@ export interface TerrainSurfaceColorConfig {
   modelPath?: string;
   tileSize?: number;
 }
+
+export interface TerrainSurfaceSample {
+  rgb: TerrainSurfaceRgb;
+  key: string | null;
+  config: TerrainSurfaceColorConfig | null;
+}

src/utils/world/terrainSurfaceSampler.ts

@@ -0,0 +1,106 @@
+import type * as THREE from "three";
+import { TERRAIN_COLORS } from "@/data/world/terrainConfig";
+import type {
+  TerrainSurfaceBounds,
+  TerrainSurfaceRgb,
+  TerrainSurfaceSample,
+  TerrainSurfaceUv,
+} from "@/types/world/terrainSurface";
+import { getTerrainColorKeyFromRgb } from "@/utils/world/terrainSurfaceColor";
+
+type TerrainSurfaceImageSource =
+  | HTMLImageElement
+  | HTMLCanvasElement
+  | ImageBitmap;
+
+const imageDataCache = new WeakMap<TerrainSurfaceImageSource, ImageData>();
+
+function clamp01(value: number): number {
+  return Math.min(Math.max(value, 0), 1);
+}
+
+function isTerrainSurfaceImageSource(
+  value: unknown,
+): value is TerrainSurfaceImageSource {
+  return (
+    value instanceof HTMLImageElement ||
+    value instanceof HTMLCanvasElement ||
+    (typeof ImageBitmap !== "undefined" && value instanceof ImageBitmap)
+  );
+}
+
+export function createTerrainSurfaceImageData(
+  texture: THREE.Texture,
+): ImageData | null {
+  if (typeof document === "undefined") return null;
+
+  const image = texture.image as unknown;
+  if (!isTerrainSurfaceImageSource(image)) return null;
+
+  const cachedImageData = imageDataCache.get(image);
+  if (cachedImageData) return cachedImageData;
+
+  const width = image.width;
+  const height = image.height;
+  if (width <= 0 || height <= 0) return null;
+
+  const canvas = document.createElement("canvas");
+  const context = canvas.getContext("2d");
+  if (!context) return null;
+
+  canvas.width = width;
+  canvas.height = height;
+  context.drawImage(image, 0, 0, width, height);
+
+  const imageData = context.getImageData(0, 0, width, height);
+  imageDataCache.set(image, imageData);
+  return imageData;
+}
+
+export function sampleTerrainSurfaceAtUv(
+  imageData: ImageData,
+  uv: TerrainSurfaceUv,
+): TerrainSurfaceSample {
+  const x = Math.round(clamp01(uv.u) * (imageData.width - 1));
+  const y = Math.round((1 - clamp01(uv.v)) * (imageData.height - 1));
+  const index = (y * imageData.width + x) * 4;
+
+  const rgb: TerrainSurfaceRgb = [
+    imageData.data[index] ?? 0,
+    imageData.data[index + 1] ?? 0,
+    imageData.data[index + 2] ?? 0,
+  ];
+  const key = getTerrainColorKeyFromRgb(rgb[0], rgb[1], rgb[2]);
+
+  return {
+    rgb,
+    key,
+    config: key === null ? null : TERRAIN_COLORS[key],
+  };
+}
+
+export function terrainSurfaceUvFromXZ(
+  x: number,
+  z: number,
+  bounds: TerrainSurfaceBounds,
+): TerrainSurfaceUv {
+  const width = bounds.maxX - bounds.minX;
+  const depth = bounds.maxZ - bounds.minZ;
+
+  return {
+    u: width === 0 ? 0 : (x - bounds.minX) / width,
+    v: depth === 0 ? 0 : (z - bounds.minZ) / depth,
+  };
+}
+
+export function sampleTerrainSurfaceAtXZ(
+  imageData: ImageData,
+  x: number,
+  z: number,
+  bounds: TerrainSurfaceBounds,
+): TerrainSurfaceSample {
+  return sampleTerrainSurfaceAtUv(
+    imageData,
+    terrainSurfaceUvFromXZ(x, z, bounds),
+  );
+}