move terrain color computation to GPU compute shader

src/core/game/GameMap.ts

@@ -30,6 +30,7 @@ export interface GameMap {
   isDefended(ref: TileRef): boolean;
   setDefended(ref: TileRef, value: boolean): void;
   tileStateView(): Uint16Array;
+  terrainDataView(): Uint8Array;
   isOnEdgeOfMap(ref: TileRef): boolean;
   isBorder(ref: TileRef): boolean;
   neighbors(ref: TileRef): TileRef[];
@@ -231,6 +232,10 @@ export class GameMapImpl implements GameMap {
     return this.state;
   }
 
+  terrainDataView(): Uint8Array {
+    return this.terrain;
+  }
+
   isOnEdgeOfMap(ref: TileRef): boolean {
     const x = this.x(ref);
     const y = this.y(ref);