It’s really not possible in LVGL this way. 
How does it work in EMWIN? Can you show and example? I’m always curious what we can learn from others.
@kisvegabor here is the datasheet of that library.
https://www.segger.com/downloads/emwin/UM03001
based on this documentation, here is its prototype (page 381)
void GUI_DrawLine(int x0,int y0,int x1,int y1);
I have worked with this library nearly 10 years ago. The worst library I have ever worked with.
Thank you. So if you just draw something, how will it remember that it’s there. E.g. if you reload the screen will EmWin know what you have drawn or do you need to handle all these in a “draw loop” of some kind?
Although I never used EmWin, I thought it is well-structured and professional.
On redraw event, this handling should happen. Since that library is closed source, I have no more idea.
At the time I was working with that library, I had gotten stuck with the usage of one widget and how hard I had tried and read the documents, I had no success, discussed that in their forum, they have had added that shortcoming in the next version documentation rather solving the problem.
I see, thank you! Today I’ll start writing a more detailed docs about LVGL’s custom drawing events.
However, in this case, we might want to add a dedicated solution to the chart. Let’s see if this comes up again, and if so, we will figure out something.
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