Opengl surface not properly updated when resizing the canvas

[koneklaudio]

When resizing the canvas (resizing the app window with the mouse), the opengl surface is not consistently being updated. The drawing gets shifted from the canvas frame.

Do I need to call any method in order to synchronize the opengl surface with the canvas size?

P.S.: To confirm this issue, I took the gradient.py example and changed the vertex array to match the canvas diagonal:

GL.glBufferData(GL.GL_ARRAY_BUFFER,
                            struct.pack('=ffffff',
                                        -1.0, -1.0,
                                        1.0, 1.0,
                                        -1.0, 1.0),
                            GL.GL_STATIC_DRAW)

When resizing the window, the triangle gets shifted from the canvas.

Thanks

[culler]

@koneklaudio: which platform were you using when you observed this problem?

[koneklaudio]

I am on Manjaro linux, in a pc (x86_64).

I checked that calling gl_viewport on both the event of the canvas and on every draw(), it almost solves the problem (it sometimes still does not sync, though).

Am I suposed to call gl_viewport, or should it be automatically synchronized on resizing?

Thanks

[culler]

Thanks! I think it should be automatic. We did not intend to make you call gl_viewport when the window is resized. If that is needed, then we should do it.

[unhyperbolic]

Much of the GL state is managed by the client - so I argue that it is also up to the client to do the call to glViewport. I think this is in line with GLUT. Also, the examples we provide all set the viewport themselves.

…

On Sun, Apr 27, 2025 at 1:29 PM Marc Culler ***@***.***> wrote: *culler* left a comment (3-manifolds/tkinter_gl#5) <#5 (comment)> Thanks! I think it should be automatic. We did not intend to make you call gl_viewport when the window is resized. If that is needed, then we should do it. — Reply to this email directly, view it on GitHub <#5 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJOP3S5SJMGF2P5FI2M4UT23U43ZAVCNFSM6AAAAAB36SX5T6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMZTGYZDONJTG4> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[culler]

Matthias, thanks for herding me back towards the KISS and minimality goals of this project. However, I suspect that there is an issue here which needs addressing. I don't think the glViewport calls should be necessary. (They apparently do not completely solve the problem, plus the resize of the X OpenGL canvas should be handled by X, based on the configure notifications sent to the server by Tk.) One bit of evidence for my suspicion is that I tried @koneklaudio's modification of the gradient demo on macOS, and there was no issue. The black triangle always fills exactly half of the canvas no matter how the window is resized.

I suspect that this may be related to the mysterious resizing InsideView window that we encountered with SnapPy on linux. More specifically, I suspect that this may have to do with the "wrapper" window, which is a window managed by the X server that is slightly larger than the Tk toplevel, and includes the window frame decorations as well as an invisible buffer region that is used to decide when to activate the resize cursor for an X window. I think we may be computing an offset or a size incorrectly, somewhere in the X11 port, possibly because we are are not accounting for the wrapper correctly