Tasmota/lib/libesp32_lvgl/lv_lib_png

PNG decoder for LVGL

Allow the use of PNG images in LVGL. This implementation uses lodepng library.

Get started

• Download or clone this repository
  • Download from GitHub
  • Clone: git clone https://github.com/littlevgl/lv_lib_png.git
• Include the library: #include "lv_lib_png/lv_png.h"
• Initalize the decocer with lv_png_init()
• Test with the following code:

    LV_IMG_DECLARE(png_decoder_test);
    lv_obj_t * img = lv_img_create(lv_scr_act(), NULL);
    lv_img_set_src(img, &png_decoder_test);

Use PNG images from file

By deafult lodepng uses C file IO API (e.g. fopen) and images can be opened like this:

lv_img_set_src(img, "./lv_lib_lodepng/png_decoder_test.png");

If you want to make lodepng to use LVGL's file system API add #define LV_PNG_USE_LV_FILESYSTEM 1 to the end of yourlv_conf.h. In this case you need to register a driver fo LVGL. The following functions are required:

• open_cb()
• read_cb()
• close_cb()
• size_cb()

After that fiels can be opened like this:

lv_img_set_src(img, "P:lv_lib_lodepng/png_decoder_test.png");

Note that the path of the file might be different.

Use PNG images from flash

To store a PNG image in flash it needs to be converted to C array with Online Image converter. Choose Raw with alpha Color format and C array Output format. Copy the result C array to your project and use it like this:

    LV_IMG_DECLARE(my_test_img);
    lv_obj_t * img = lv_img_create(lv_scr_act(), NULL);
    lv_img_set_src(img, &my_test_img);

Learn more

To learn more about the PNG decoder itself read this blog post

To learn more about the Image decoder interface of LittlevGL read the realevant part of the documentation.