Example with Tcl/Tk

[nico-robert]

Hello ,
I would like to use your lib in Tcl / Tk, but my knowledge of python is poor.
Could you show me an example in Tcl, so far here's what I've done :

package req Tkgl
update idletasks
tkgl .gl -profile "3_2"
.gl makecurrent
# my lib openGl 
gl::glClearColor 0.0 1.0 1.0 0.0
gl::glClear      {GL_COLOR_BUFFER_BIT GL_DEPTH_BUFFER_BIT}
.gl swapbuffers
pack .gl

My window appears but disappears after a few seconds.
Can you tell me if the above example is correct?
Thanks

[culler]

I added a test sctipt called clear.tcl which does the same thing as clear.py. I have only tested this on macOS so far.

No matter which language you use, you need to also have a wrapper for the OpenGL library. In our python test scripts we use PyOpenGL. For clear.tcl I used the package tcl3dogl, which is included as part of tcl3d. The clear.tcl script expects to be able to load tcl3dogl. I don't know what you are using, or whether that matters.

I can't say for sure what is causing your trouble, but I would expect your pack command to come before the call to makecurrent. I don't know what state the GL context is in before the widget has been mapped. Possibly that depends on the platform. You don't say which platform you are using.

[nico-robert]

I have tested the same code as you (I had to add update idletasks to your code).
I'm on Windows 10 Tcl/Tk 8.6.13 or Tcl/Tk 9.0.1.
I have the same behavior as with my OpenGL lib, the window appears for a few seconds and then disappears.
I compiled with BAWT to get tcl3dogl, here is my result :

[nico-robert]

I'll try to test it on MacOs, if I can compile Tcl3D.

[culler]

I am guessing that this is a Windows timing issue. Somehow the Python overhead includes enough of a delay to ensure that OpenGL calls do not happen before the OpenGL context is ready for them. The fact that you had to call update idle tasks supports this theory. But that alone was not sufficient.

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[nico-robert]

I have tested on macOS (Tcl/Tk 8.6.16) and It works. I didn't need to call the update idletasks command.As you said, it's a problem on Windows, tomorrow I'll test with the version of Tcl/Tk 8.6.16 on Windows just in case.

[nico-robert]

I'll test with the version of Tcl/Tk 8.6.16 on Windows just in case

Same thing, the window appears for a few seconds and then disappears.

[culler]

I finally managed to build tcl3dOgl on Windows so I could test clear.tcl on Windows, I learned several things:

• The Tcl3d installer does not install a tcl3dOgl package, whether or not you install the "Batteries Included" version. So my claim that tcl3dOgl is available with Tcl3d is misleading.
• Building tcl3dOgl on Windows is non-trivial. First you have to use an old version of CMake. Second, the Windows build requires an installation of SWIG, which is not the case for other platforms. Third, there are several environment variables that you have to get right and that are not documented. Fourth, you have to assemble your own Tcl package if you only want tcl3dOgl. Maybe I will distribute a standalone tcl3dOgl package,
• Once I had tcl3dOgl available, I found that running the clear.tcl script would segfault. I did not see a window appear for a second and then disappear. I just got a segfault when the tkgl widget was created.
• A workaround for the segfault turned out to be calling update idletasks after loading the tkgl package but before creating a tkgl widget. This is clearly a Windows specific bug in tkgl. I suppose I could work around it with a hack like calling update idletasks inside the pkgIndex.tcl script. But I would rather understand what is causing the segfault, which will take some work. Some part of the opengl initialization is apparently not happening when the package is loaded, but happens some time after the event loop starts running.
• Once I added the call to update idletasks the clear.tcl script worked fine. No disappearing windows. No crashes.

[nico-robert]

I've cloned your repo and recompiled your sources , it works. (except that you need to add the update idletasks command on Windows )
I had used your dlls from this repo which seems to have a different behaviour from my side.
Thank you for your feedback. I will try to integrate your package into my project