File System Interfaces
LVGL has a File System (lv_fs_drv) module to provide an abstraction layer for various file system drivers.
LVG has built in support for:
STDIO (Linux and Windows using C standard function .e.g
fopen,fread)POSIX (Linux and Windows using POSIX function .e.g
open,read)WIN32 (Windows using Win32 API function .e.g
CreateFileA,ReadFile)MEMFS (read a file from a memory buffer)
LITTLEFS (a little fail-safe filesystem designed for microcontrollers)
Arduino ESP LITTLEFS (a little fail-safe filesystem designed for Arduino ESP)
Arduino SD (allows for reading from and writing to SD cards)
You still need to provide the drivers and libraries, this extension provides only the bridge between FATFS, STDIO, POSIX, WIN32 and LVGL.
Usage
In lv_conf.h enable LV_USE_FS_... and assign an upper cased
letter to LV_FS_..._LETTER (e.g. 'S'). After that you can access
files using that driver letter. E.g. "S:path/to/file.txt".
Working with common prefixes
A default driver letter can be set by LV_FS_DEFAULT_DRIVE_LETTER,
which allows skipping the drive prefix in file paths.
For example if LV_FS_DEFAULT_DRIVE_LETTER is set the 'S' "path/to/file.txt" will mean "S:path/to/file.txt".
This feature is useful if you have only a single driver and don't want to bother with LVGL's driver layer in the file paths. It also helps to use a unified path with LVGL's file system and normal file systems. The original mechanism is not affected, so a path starting with drive letter will still work.
The working directory can be set with LV_FS_..._PATH. E.g.
"/home/joe/projects/" The actual file/directory paths will be
appended to it, allowing to skip the common part.
Caching
Cached reading is also supported if LV_FS_..._CACHE_SIZE is set to
not 0 value. lv_fs_read() caches this size of data to lower the
number of actual reads from the storage.
To use the memory-mapped file emulation an lv_fs_path_ex_t object must be
created and initialized. This object can be passed to lv_fs_open() as
the file name:
lv_fs_path_ex_t mempath;
lv_fs_file_t file;
uint8_t *buffer;
uint32_t size;
/* Initialize buffer */
...
lv_fs_make_path_from_buffer(&mempath, LV_FS_MEMFS_LETTER, (void*)buffer, size);
lv_fs_res_t res = lv_fs_open(&file, (const char *)&mempath, LV_FS_MODE_RD);