How to get the SDL example working on Linux?

[glennra]

I have built the unix version (fee49e2) (on Debian Testing) following the instructions in the readme.

python3 make.py unix DISPLAY=sdl_display INDEV=sdl_pointer

When running the sample code from the readme:

https://github.com/lvgl-micropython/lvgl_micropython?tab=readme-ov-file#python-code-examples

I see a window flash onto the screen and then disappear. There are no errors reported.

If I add:

  import time
  while True:
      time.sleep(1)

The window stays but nothing is drawn in it.

How can I get this working?

[kdschlosser]

add the code to a python source file and put that file into the same folder as the binary. Run the binary without passing the filename. When the repl comes up import the python source file.

[glennra]

How hard would it be to add an automatic import of boot.py like some of the standard micropython ports do?
I can't check right now but I'm assuming the lvgl micropython builds for those boards also do this.

[kdschlosser]

In order to make it all work properly you need to add a loop at the end of the file you are passing when executing the binary.

import time

while True:
    time.sleep_ms(5)
    lcd_bus._pump_main_thread()

That needs to be added because of how micropython is written. when running the binary without passing a filename the repl loads and it will loop. during hat loop it check to see if there are any scheduled tasks that need to run in the main thread. This is an important piece because a task gets scheduled to run in order for LVGL to update. when passing in a file name the repl is bypassed so no loop occurs. Now you simply cannot add a loop at the end of the file you want to run because no running of scheduled tasks takes place. That is the reason why I added the function call to the binding. so now you can add the loop and make that function call so LVGL will then update properly.

[glennra]

In my sdl.py file I now have this function, which allows the program to exit when the window is closed.

import time
def event_loop():
    while lv.screen_active(): # exit when the screen is closed
        time.sleep_ms(5)
        lcd_bus._pump_main_thread()

after the lvgl init code I call sdl.event_loop().

... in case others find this useful.

[kdschlosser]

I did a pretty good job at thinking of all the possible oddities that could come up and how to make it work.