Weird jittery behavior when background() is not called in draw() while using the skia renderer.

[procub3r]

Describe the bug
When background() is not called in draw(), there is a weird jittery behavior that is observed while the graphics are being rendered using the skia renderer.

To Reproduce
Run an example program:

from p5 import *

def size():
    pass

def draw():
    # Do not call background() here.
    circle(mouse_x, mouse_y, 50)

run(renderer='skia')

Expected behavior
Smooth rendering without any weird jittery behavior.

Screen capture

jittery.mov

System information:

• p5 release: Current master branch 8f4777b
• Python version: 3.10.10
• Operating system: Windows 11

Additional context
#423 (comment)

[github-actions]

Thank you for submitting your first issue to p5py

[tushar5526]

This seems to be related to some bug with swapping of frame buffer and this was not the case earlier. I think a good strategy would be to go a few commits back and identify for the buggy commit

[tushar5526]

6b079cf -- This is the commit that produced this bug. Things are working fine before this commit. Would you like to do a fix for this ?

[tushar5526]

We only need to disable this line - 6b079cf#diff-7a18b014da674a8330d705e9c488589c23a673a0062af59d7d1e1270181f673aL80 and test it on windows and then check for a possible fix.

[procub3r]

Cool! I'll get in on this.

[procub3r]

I'm slightly confused 😅
What do you mean by disabling that line? That line doesn't exist in the master branch anymore.

Adding back all three of those lines seems to work (yet to test on windows though).

[procub3r]

Adding back all three of those lines seems to error out on windows. This is the error that I get:

Traceback (most recent call last):
  File "c:\dev\p5dev\test\main.py", line 9, in <module>
    run(renderer='skia')
  File "C:\Users\procub3r\AppData\Local\Programs\Python\Python310\lib\site-packages\p5\sketch\userspace.py", line 231, in run
    p5.sketch.start()
  File "C:\Users\procub3r\AppData\Local\Programs\Python\Python310\lib\site-packages\p5\sketch\Skia2DRenderer\base.py", line 159, in start
    self.window = self.glfw_window()
  File "C:\Users\procub3r\AppData\Local\Programs\Python\Python310\lib\site-packages\p5\sketch\Skia2DRenderer\base.py", line 80, in glfw_window
    GL.glEnable(GL.GL_MULTISAMPLE)
  File "C:\Users\procub3r\AppData\Local\Programs\Python\Python310\lib\site-packages\OpenGL\platform\baseplatform.py", line
415, in __call__
    return self( *args, **named )
  File "src/errorchecker.pyx", line 58, in OpenGL_accelerate.errorchecker._ErrorChecker.glCheckError
OpenGL.error.GLError: GLError(
        err = 1282,
        description = b'invalid operation',
        baseOperation = glEnable,
        cArguments = (GL_MULTISAMPLE,)
)

Adding back just the first two lines and commenting out GL.glEnable(GL.GL_MULTISAMPLE) doesn't produce an error but it doesn't fix the issue either. The jittery behavior persists.

[procub3r]

My initial thought was that maybe the buffers were being swapped more than once in a single frame due to some bug. But I've just tested it and that doesn't seem to be the case.

Unrelated note: I don't quite understand the role GL.glEnable(GL.GL_MULTISAMPLE) plays here.
I mean for some reason, when I add that line in, the jittery behavior stops on linux and it works smoothly. But it simply errors out on windows.

[tushar5526]

Sorry for all the confusion. I removed those 3 lines to remove the error that you were facing. Those lines are some configurations for GLFW related to anti-aliasing etc. you can read about them in the glfw docs.

I mean for some reason, when I add that line in, the jittery behavior stops on linux and it works smoothly. But it simply errors out on windows.

This is what we have to fix for. Research why its throwing error on windows and workarounds for it.

[tushar5526]

#399 - more context for you.

[procub3r]

Thanks for the clarification! I know what to do now :D

[tushar5526]

Closed by #446