Tried to update CEF to 91 but had issued with OSR

[Xavier Cho]

Hi,

I know that this isn't directly related to the main repository but to a fork of it, which is https://github.com/miilO/cefpython.

But I have no other place to ask a question about updating CefPython so please bear with me.

I tried to `cefpython91` branch from the mentioned fork and managed to make it mostly work on my Linux/Python 3.10 environment.

However, when I try to run it in offscreen rendering mode, it either never invoke OnPaint callback or opening up actual browser window.

Below is the minimal example that reproduces the problem:

############################################

from cefpython3 import cefpython as cef
import sys

class RenderHandler:

   def GetViewRect(self, rect_out, **_) -> bool:
       print("#### GetViewRect")
       rect_out.extend([0, 0, 800, 600])

       return True

   def OnPaint(self, browser, element_type, paint_buffer, **_) -> None:
       print("#### OnPaint")

def main():
   settings = {
       "windowless_rendering_enabled": True,
   }

   switches = {
       # "log-severity": "verbose",
       "disable-gpu": "",
       "disable-gpu-compositing": "",
       "disable-extensions": "",
   }

   sys.excepthook = cef.ExceptHook  # To shutdown all CEF processes on error
   cef.Initialize(settings=settings, switches=switches)

   window_info = cef.WindowInfo()
   window_info.SetAsOffscreen(0)

   browser = cef.CreateBrowserSync(url="https://www.google.com/", window_info=window_info)

   browser.SetClientHandler(RenderHandler())
   browser.WasResized()

   cef.MessageLoop()

if __name__ == '__main__':
   main()

############################################

What feels strange is, GetViewRect is only invoked (still, not OnPaint or OnAcceleratedPaint) when I provide an invalid window handle to SetAsOffscreen, otherwise it justs opens up a browser window.

My intended use case is to run it from a game loop (with UPBGE, to be specific) and I could observe a similar behaviour in that environment with a slight twist.

In that case, any invocation of the game engine's API or even simple Python's builtin functions like `print` makes the code invoke GetViewRect without calling OnPaint/OnAcceleratedPaint. And if I just initialise CEF, it will open an actual browser like my above example.

I bisected the CEF/CefPython builds and managed to track down the problematic changes to be those between 72 and 73. Up until 72 (`cefpython72`), I could run the same code correctly in OSR mode.

I suspect it might have something to do with threading but I have no real clue.

If anyone could provide some insight, hints, or just any suggestion as to potential way to fix this problem, it'd be much appreciated.

Thanks!

Xavier

P.S.: (To miilO) If you happen to read this, please consider providing some way I could report issues or contribute to the code.