Eager load used sprites

internal/assetstore/map.go

@@ -62,6 +62,21 @@ func (a *AssetStore) Map(name string) (*Map, error) {
 	return m, nil
 }
 
+func (m *Map) LoadSprites() error {
+	// Eager load the sprites we use
+	for x := m.Rect.Min.X; x <= m.Rect.Max.X; x++ {
+		for y := m.Rect.Min.Y; y <= m.Rect.Max.Y; y++ {
+			for z := 0; z < maps.MaxHeight; z++ {
+				if _, err := m.SpritesForCell(x, y, z); err != nil {
+					return err
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
 // SpritesForCell returns the sprites needed to correctly render this cell.
 // They should be rendered from first to last to get the correct ordering
 func (m *Map) SpritesForCell(x, y, z int) ([]*Sprite, error) {