There are several options for working with resources in Android via ndk – C++:
- Use access to resources from an apk file using AssetManager
- Download resources from the Internet and unpack them into the application directory, use them using standard C++ methods
- Combined method – get access to the archive with resources in apk via AssetManager, unpack them into the application directory, then use them using standard C++ methods
Next I will describe the combined access method used in the Flame Steel Engine.
When using SDL, you can simplify access to resources from apk, the library wraps calls to AssetManager, offering interfaces similar to stdio (fopen, fread, fclose, etc.)
SDL_RWops *io = SDL_RWFromFile("files.fschest", "r");
After loading the archive from apk to the buffer, you need to change the current working directory to the application directory, it is available for the application without obtaining additional permissions. To do this, we will use a wrapper on SDL:
chdir(SDL_AndroidGetInternalStoragePath());
Next, we write the archive from the buffer to the current working directory using fopen, fwrite, fclose. After the archive is in a directory accessible to C++, we unpack it. Zip archives can be unpacked using a combination of two libraries – minizip and zlib, the first one can work with the archive structure, while the second one unpacks the data.
For more control, ease of porting, I have implemented my own zero-compression archive format called FSChest (Flame Steel Chest). This format supports archiving a directory with files, and unpacking; There is no support for folder hierarchy, only files can be worked with.
We connect the FSChest library header, unpack the archive:
#include "fschest.h"
FSCHEST_extractChestToDirectory(archivePath, SDL_AndroidGetInternalStoragePath());
After unpacking, the C/C++ interfaces will have access to the files from the archive. Thus, I did not have to rewrite all the work with files in the engine, but only add file unpacking at the startup stage.
Sources
https://developer.android.com/ndk/ reference/group/asset
Source Code
https://gitlab.com/demensdeum/space- jaguar-action-rpg
https://gitlab.com/demensdeum/fschest
