feat: initialize mini program map engine

miniprogram/utils/tile.ts

@@ -0,0 +1,61 @@
+export interface TileItem {
+  key: string
+  url: string
+  x: number
+  y: number
+  leftPx: number
+  topPx: number
+  sizePx: number
+  isCenter: boolean
+}
+
+const TILE_OVERLAP_PX = 2
+
+export interface TileGridOptions {
+  urlTemplate: string
+  zoom: number
+  centerTileX: number
+  centerTileY: number
+  viewportWidth: number
+  viewportHeight: number
+  tileSize: number
+  overdraw: number
+}
+
+export function buildTileUrl(template: string, z: number, x: number, y: number): string {
+  return template
+    .replace('{z}', String(z))
+    .replace('{x}', String(x))
+    .replace('{y}', String(y))
+}
+
+export function createTileGrid(options: TileGridOptions): TileItem[] {
+  const tiles: TileItem[] = []
+  const halfWidth = options.viewportWidth / 2
+  const halfHeight = options.viewportHeight / 2
+  const horizontalRange = Math.ceil(halfWidth / options.tileSize) + options.overdraw
+  const verticalRange = Math.ceil(halfHeight / options.tileSize) + options.overdraw
+
+  for (let dy = -verticalRange; dy <= verticalRange; dy += 1) {
+    for (let dx = -horizontalRange; dx <= horizontalRange; dx += 1) {
+      const x = options.centerTileX + dx
+      const y = options.centerTileY + dy
+
+      const rawLeft = halfWidth + (dx - 0.5) * options.tileSize
+      const rawTop = halfHeight + (dy - 0.5) * options.tileSize
+
+      tiles.push({
+        key: `${options.zoom}-${x}-${y}`,
+        url: buildTileUrl(options.urlTemplate, options.zoom, x, y),
+        x,
+        y,
+        leftPx: Math.floor(rawLeft - TILE_OVERLAP_PX / 2),
+        topPx: Math.floor(rawTop - TILE_OVERLAP_PX / 2),
+        sizePx: Math.ceil(options.tileSize) + TILE_OVERLAP_PX,
+        isCenter: dx === 0 && dy === 0,
+      })
+    }
+  }
+
+  return tiles
+}