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Lottie player

Allows to use Lottie animations in LVGL. Taken from this base repository

LVGL provides the interface to Samsung/rlottie library's C API. That is the actual Lottie player is not part of LVGL, it needs to be built separately.

Build Rlottie

To build Samsung's Rlottie C++14-compatible compiler and optionally CMake 3.14 or higher is required.

To build on desktop you can follow the instructions from Rlottie's README. In the most basic case it looks like this:

mkdir rlottie_workdir
cd rlottie_workdir
git clone https://github.com/Samsung/rlottie.git
mkdir build
cd build
cmake ../rlottie
make -j
sudo make install

And finally add the -lrlottie flag to your linker.

On embedded systems you need to take care of integrating Rlottie to the given build system.

Usage

You can use animation from files or raw data (text). In either case first you need to enable LV_USE_RLOTTIE in lv_conf.h.

The width and height of the object be set in the create function and the animation will be scaled accordingly.

Use Rlottie from file

To create a Lottie animation from file use:

  lv_obj_t * lottie = lv_rlottie_create_from_file(parent, width, height, "path/to/lottie.json");

Note that, Rlottie uses the standard STDIO C file API, so you can use the path "normally" and no LVGL specific driver letter is required.

Use Rlottie from raw string data

lv_example_rlottie_approve.c contains an example animation in raw format. Instead storing the JSON string a hex array is stored for the following reasons:

  • avoid escaping " in the JSON file
  • some compilers don't support very long strings

lvgl/scripts/filetohex.py can be used to convert a Lottie file a hex array. E.g.:

./filetohex.py path/to/lottie.json > out.txt

To create an animation from raw data:

extern const uint8_t lottie_data[];
lv_obj_t* lottie = lv_rlottie_create_from_raw(parent, width, height, (const char *)lottie_data);

Getting animations

Lottie is standard and popular format so you can find many animation files on the web. For example: https://lottiefiles.com/

You can also create your own animations with Adobe After Effects or similar software.

Controlling animations

LVGL provides two functions to control the animation mode: lv_rlottie_set_play_mode and lv_rlottie_set_current_frame. You'll combine your intentions when calling the first method, like in these examples:

lv_obj_t * lottie = lv_rlottie_create_from_file(scr, 128, 128, "test.json");
lv_obj_center(lottie);
// Pause to a specific frame
lv_rlottie_set_current_frame(lottie, 50);
lv_rlottie_set_play_mode(lottie, LV_RLOTTIE_CTRL_PAUSE); // The specified frame will be displayed and then the animation will pause

// Play backward and loop
lv_rlottie_set_play_mode(lottie, LV_RLOTTIE_CTRL_PLAY | LV_RLOTTIE_CTRL_BACKWARD | LV_RLOTTIE_CTRL_LOOP);

// Play forward once (no looping)
lv_rlottie_set_play_mode(lottie, LV_RLOTTIE_CTRL_PLAY | LV_RLOTTIE_CTRL_FORWARD);

The default animation mode is play forward with loop.

If you don't enable looping, a LV_EVENT_READY is sent when the animation can not make more progress without looping.

To get the number of frames in an animation or the current frame index, you can cast the lv_obj_t instance to a lv_rlottie_t instance and inspect the current_frame and total_frames members.

Example


.. include:: ../../examples/libs/rlottie/index.rst

API


.. doxygenfile:: lv_rlottie.h
  :project: lvgl