Allow the use of PNG images in LVGL.
Detailed introduction: https://github.com/lvandeve/lodepng
If enabled in lv_conf.h by :cLV_USE_LODEPNG LVGL will register a new image decoder automatically so PNG files can be directly used as any other image sources.
- Note
a file system driver needs to be registered to open images from
files. Read more about it overview_file_system or just enable one in lv_conf.h with LV_USE_FS_...
The whole PNG image is decoded, so width x height x 4 bytes free RAM space is required. The decoded image is stored in RGBA pixel format.
As it might take significant time to decode PNG images LVGL's overview_image_caching feature can be useful.
PNG file format supports True color (24/32 bit), and 8-bit palette colors. Usually cliparts, drawings, icons and simple graphics are stored in PNG format, that do not use the whole color space, so it is possible to compress further the image by using 8-bit palette colors, instead of 24/32 bit True color format. Because embedded devices have limited (flash) storage, it is recommended to compress images.
One option is to use a free online PNG compressor site, for example Compress PNG: https://compresspng.com/
lodepng