Using jogl and Offscreen leads to "No OpenGL context current on this thread" error

[davidbilge]

When starting my App with Type.OffscreenSurface and a JOGL_ renderer, I get a No OpenGL context current on this thread error.

The problem seems to be that JoglOffscreenBuffer calls GLContext.getCurrentGL() in a new Thread and there is no GLContext attached to that thread.

This applies to 3.1.0-beta1.

Hi. Please provide a SSCCE: http:sscce.org I'm going to look at the source code. By the way, please post the full stack trace.

The problem is probably here: https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-jogl/src/main/java/com/jme3/system/jogl/JoglOffscreenBuffer.java#L64 It just stupidly mimics the way another similar API is used. There is no current OpenGL context here. I can fix this bug when I'm at home in a few hours. You can comment those lines and rebuild JMonkeyEngine in the meantime.

Actually, those lines are useless as JOGL can create an offscreen buffer even with no full FBO support. I have to add those lines too but it doesn't concern your bug: if (settings.getRenderer().equals(AppSettings.JOGL_OPENGL_FORWARD_COMPATIBLE)) {
caps = new GLCapabilities(GLProfile.getMaxProgrammable(true));
} else {
caps = new GLCapabilities(GLProfile.getMaxFixedFunc(true));
}

I'll fix it in about 11 hours, sorry for the delay.

[davidbilge]

I made some modifications too: https://gist.github.com/davidbilge/d19f5fbcc5650ba4432ecf30467c5047

Your modifications are wrong. At first, making the OpenGL context current in this method isn't a good idea, it's useless as the OpenGL call was only used to check whether FBOs are supported (rather call GLContext.hasFullFBOSupport() if you really need to know that). Secondly, you shouldn't have to force the renderer in this method, call settings.setRenderer(AppSettings.JOGL_OPENGL_BACKWARD_COMPATIBLE) elsewhere. Moreover, your source code uses a different profile to create the offscreen buffer and to create the renderer.

[davidbilge]

Yeah, about setting the renderer: I had to do that because I use my "CustomJoglOffscreenBuffer" by configuring a CUSTOMrenderer in my AppSettings - and if I do that, JoglContext complains about an "unsupported renderer" in line 189. This is really just a workaround to get my custom implementation to work.

If I don't make the GLContext current, I get this Exception:

Exception in thread "jME3 Main" java.lang.NullPointerException
    at com.jme3.system.jogl.JoglContext.initContextFirstTime(JoglContext.java:157)
    at com.jme3.system.jogl.JoglContext.internalCreate(JoglContext.java:221)
    at com.example.jmonkeytest.CustomJoglOffscreenBuffer.initInThread(CustomJoglOffscreenBuffer.java:59)
    at com.example.jmonkeytest.CustomJoglOffscreenBuffer.run(CustomJoglOffscreenBuffer.java:100)
    at java.lang.Thread.run(Thread.java:745)

Ok thank you for your detailed explanations. Please be very accurate on what you are trying to do. You would have had a similar concern with the other available backends. Please rather use something like "JOGLCustom" instead of "CUSTOM" and it will work. I'll fix the null dereference too, it might require much time than I thought.

[davidbilge]

In JmeDesktopSystem#284 the custom renderer name is expected to start with "CUSTOM", hence the choice. To be precise, I used settings.setRenderer("CUSTOMcom.example.jmonkeytest.CustomJoglOffscreenBuffer");.

Yes but actually you can't use a custom renderer without creating your own JMonkeyEngine context and none of the implementation of JmeContext are designed to be extended, which explains why you obtained an UnsupportedOperationException. In my humble opinion, there are two bugs to fix. At first, please check whether creating an offscreen renderer with the JOGL backend works as is (which is probably not the case). Then, I'll do my best to fix your specific use case with a custom offscreen buffer but it will only work with the JOGL backend (which is ok for me as a JogAmp maintainer officially responsible for engine support).

[davidbilge]

Thank you for you effort. I do not actually want to use a custom offscreen buffer. I only did that in this case to be able to pinpoint the bugs in the official implementation. As soon as they are fixed I can easily use the standard way.

Using offscreen mode does not work with the jogl backend as of now—it does if the fixes from my custom version are applied, though.

Am 30.04.2016 um 10:47 schrieb Julien Gouesse notifications@github.com:

Yes but actually you can't use a custom renderer without creating your own JMonkeyEngine context and none of the implementation of JmeContext are designed to be extended, which explains why you obtained an UnsupportedOperationException. In my humble opinion, there are two bugs to fix. At first, please check whether creating an offscreen renderer with the JOGL backend works as is (which is probably not the case). Then, I'll do my best to fix your specific use case with a custom offscreen buffer but it will only work with the JOGL backend (which is ok for me as a JogAmp maintainer officially responsible for engine support).

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You're welcome. This feature is already working in JogAmp's Ardor3D Continuation, I'll try to do something similar in JMonkeyEngine.

I will modify the classes extending JoglContext so that they use the GLContext of the drawable when it is possible and I will remove the useless tests.

Please let me know whether it works. I'm not sure that I should release the OpenGL context. The other offscreen canvases that I implemented do something similar to what you did when they use a pbuffer but the most reliable one simply uses a NEWT offscreen GLWindow and is a lot cleaner.

[shadowislord]

The fix has already been committed, going to close the issue