LVGL clear screen

[ChrisVonFrosta]

How to clear the screen?
even after reboot the screen keeps the content.
i tried:

lv.obj_clean(lv.scr_act());
BRY: Exception> 'attribute_error' - module 'lv' has no member 'obj_clean'

[s-hadinger]

At boot the splash screen is displayed and the screen is then cleared after 5 seconds if lvgl is not used.

Can you describe your problem in more details?

[sfromis]

I was only pointing out how the method call for clean was not "missing", as it is documented where it is. Not suggesting that it would be a solution for you.

Specifically, I'd not expect the clean() method (not clear) to communicate with the display about erasing (or clearing) contents, only to cleanup based internal objects already in LVGL. Hence my expectation would be that the clean() method would already not make sense "immediately after lv.start".

And some display types may have a buffer as part of the display controller, instead of depending on refresh from the host. In some situation I've even seen display content linger after restarting Tasmota, but I don't remember any details of that.

Do note that I'm not doing much at the LVGL level (mostly using HASPmota), and can't really tell you how to do things. And without demonstration code to recreate your issue, no basis for even making guesses.

I'm seeing the restart button for a long time, when having the debug option enabled.

However, as LVGL is not part of Berry, I'm not sure that restarting the Berry VM should be "expected" to reinitialize displays at a "lower level".

[augea]

Well, after a BrRestart all widgets are still visible on the screen.
If lv.start() would clear all LVGL resouces it would be fine for me.
Can somebody confim this?

[s-hadinger]

No, lv.start() is just used to start LVGL the first time. Any other call to lv.start() does nothing.

LVGL has its own life, independent from Berry. So calling BrRestart does not clear anything in LVGL. Actually it is even worse, because some memory allocated by Berry may be used by LVGL. Freeing all this memory can cause LVGL to crash.

What are you trying to do?

• Refresh the screen?
• Clear everything you defined in LVGL
• Or just temporarily clear the screen to display its content back later? If this is what you want, there are ways, like creating a new screen object and swap the current screen. Or put a black rectangle in front of all objects (basically what is used for screen saving)

[augea]

Yes, I’m trying to clean resources allocated by LVGL.
During testing I have to restart the program several times but widgets are not cleared from screen without a complete ESP reboot.
I.e. if you set a button and change its position by changing and reentering the program you get the old button and the new button placed over each other.
See also Berry restarts when deleting a not active screen (LVGL) #23327 (same project)
Im' looking for a way to release all and parts of the resources allocated by LVGL.

[s-hadinger]

The only way to release resources allocated by LVGL is to explicitly ask LVGL to delete all objects one by one. This means that you need to call <obj>.delete() on each object.

[augea]

I understand what you wrote. However, I'd like to ask again specifically. So, deleting the parent object (like the screen object) doesn't work, but rather requires deleting each object separately? That would be different from the LVGL documentation, and the solution is different in Berry on Tasmota.

There is a common delete function for all object types. It deletes the object and all of its children.
see
https://docs.lvgl.io/8.3/overview/object.html

[s-hadinger]

Berry does a direct mapping of lvgl objects. As said this part is not deeply tested. So yes deleting the parent object should remove sub-objects in lvgl. But you need to be cautious of not leaving Berry references either or the memory won't be freed