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OpenGL X11 + OpenGL causes segfault

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I'm having issues getting X11 to work with OpenGL. I've tried everything! It used to work with GLFW but I'm trying to get it to work with GLX instead, and Win32 currently works, so this is very system-dependent. Why does the program segfault when it reaches either glClear, glClearColor, or glGetString? Thanks in advance!

This all lies inside a function, Initialize(), of a class X11Window. There is barely any code that happens before. I have NVidia drivers installed.

display = XOpenDisplay(NULL);
if (display == NULL) {
std::cout << "Could not open display\n";
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);


// Check GLX version
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
else {
std::cout << "GLX client version: " << glXGetClientString(display, GLX_VERSION) << '\n';
std::cout << "GLX client vendor: " << glXGetClientString(display, GLX_VENDOR) << "\n";
std::cout << "GLX client extensions:\n\t" << glXGetClientString(display, GLX_EXTENSIONS) << "\n";

std::cout << "GLX server version: " << glXQueryServerString(display, screenId, GLX_VERSION) << "\n";
std::cout << "GLX server vendoe: " << glXQueryServerString(display, screenId, GLX_VENDOR) << "\n";
std::cout << "GLX server extensions:\n\t " << glXQueryServerString(display, screenId, GLX_EXTENSIONS) << "\n";
}

GLint glxAttribs[] = {
GLX_X_RENDERABLE , True,
GLX_DRAWABLE_TYPE , GLX_WINDOW_BIT,
GLX_RENDER_TYPE , GLX_RGBA_BIT,
GLX_X_VISUAL_TYPE , GLX_TRUE_COLOR,
GLX_RED_SIZE , 8,
GLX_GREEN_SIZE , 8,
GLX_BLUE_SIZE , 8,
GLX_ALPHA_SIZE , 8,
GLX_DEPTH_SIZE , 24,
GLX_STENCIL_SIZE , 8,
GLX_DOUBLEBUFFER , True,
None
};

int fbcount;
GLXFBConfig* fbc = glXChooseFBConfig(display, screenId, glxAttribs, &fbcount);
if (fbc == 0) {
std::cout << "Failed to retrieve framebuffer.\n";
XCloseDisplay(display);
return 1;
}
std::cout << "Found " << fbcount << " matching framebuffers.\n";

// Pick the FB config/visual with the most samples per pixel
std::cout << "Getting best XVisualInfo\n";
int best_fbc = -1, worst_fbc = -1, best_num_samp = -1, worst_num_samp = 999;
for (int i = 0; i < fbcount; ++i) {
XVisualInfo *vi = glXGetVisualFromFBConfig( display, fbc[i] );
if ( vi != 0) {
int samp_buf, samples;
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf );
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLES , &samples );
//std::cout << " Matching fbconfig " << i << ", SAMPLE_BUFFERS = " << samp_buf << ", SAMPLES = " << samples << ".\n";

if ( best_fbc < 0 || (samp_buf && samples > best_num_samp) ) {
best_fbc = i;
best_num_samp = samples;
}
if ( worst_fbc < 0 || !samp_buf || samples < worst_num_samp )
worst_fbc = i;
worst_num_samp = samples;
}
XFree( vi );
}
std::cout << "Best visual info index: " << best_fbc << "\n";
GLXFBConfig bestFbc = fbc[ best_fbc ];
XFree( fbc ); // Make sure to free this!

XVisualInfo* visual = glXGetVisualFromFBConfig( display, bestFbc );

if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}

if (screenId != visual->screen) {
std::cout << "screenId(" << screenId << ") does not match visual->screen(" << visual->screen << ").\n";
XCloseDisplay(display);
return 1;

}

// Open the window
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask | KeyPressMask | KeyReleaseMask | KeymapStateMask | PointerMotionMask | ButtonPressMask | ButtonReleaseMask | EnterWindowMask | LeaveWindowMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, game.settings.resolution.x, game.settings.resolution.y, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);

// Create GLX OpenGL context
glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );

const char *glxExts = glXQueryExtensionsString( display, screenId );
std::cout << "Late extensions:\n\t" << glxExts << "\n\n";
if (glXCreateContextAttribsARB == 0) {
std::cout << "glXCreateContextAttribsARB() not found.\n";
}

int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 3,
GLX_CONTEXT_FLAGS_ARB, 0,
GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
None
};

GLXContext context = 0;
if (!isExtensionSupported( glxExts, "GLX_ARB_create_context")) {
context = glXCreateNewContext( display, bestFbc, GLX_RGBA_TYPE, 0, True );
}
else {
context = glXCreateContextAttribsARB( display, bestFbc, 0, true, context_attribs );
}
XSync( display, False );

// Verifying that context is a direct context
if (!glXIsDirect (display, context)) {
std::cout << "Indirect GLX rendering context obtained\n";
}
else {
std::cout << "Direct GLX rendering context obtained\n";
}
glXMakeCurrent(display, window, context);

game.HandleMessage(ENGINE_MESSAGE_CONSOLE, ENGINE_MESSAGE_OUTPUT, "TEST: Made Current...\n");


std::cout << "GL Vendor: " << glGetString(GL_VENDOR) << "\n";
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GL Shading Language: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";


// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
game.HandleMessage(ENGINE_MESSAGE_CONSOLE, ENGINE_MESSAGE_OUTPUT, "TEST: Made ClearWindow...\n");

// Set GL Sample stuff
glClearColor(0.5f, 0.6f, 0.7f, 1.0f);
game.HandleMessage(ENGINE_MESSAGE_CONSOLE, ENGINE_MESSAGE_OUTPUT, "TEST:ClearColor...\n");


// Resize window
/*unsigned int change_values = CWWidth | CWHeight;
XWindowChanges values;
values.width = game.settings.resolution.x;
values.height = game.settings.resolution.y;
XConfigureWindow(display, window, change_values, &values);*/


// Enter message loop
while (true) {
ReadEvents();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}

// Cleanup
XDestroyWindow(display, window);
XCloseDisplay(display);

game.HandleMessage(ENGINE_MESSAGE_CONSOLE, ENGINE_MESSAGE_OUTPUT, "TEST: X11 Window Created...\n");
return true;

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glXMakeCurrent also has a return-code, like the single one you don't check.. :)

Probably the context isn't properly made current there.

If it is, try getting the function pointers for the normal GL functions instead of relying on them by linking.

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glXMakeCurrent also has a return-code, like the single one you don't check.. :)

Probably the context isn't properly made current there.

If it is, try getting the function pointers for the normal GL functions instead of relying on them by linking.

 

Thanks for the input Erik! It returned true, but at least now I know of a place to test for any future bugs :P So it's still not working. Any other ideas?

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Did you try glXGetProcAddress to get the glGetString function pointer instead of calling it by its prototype?

(If I understand correctly and the first glGetString call to get GL_VENDOR crashes)

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Did you try glXGetProcAddress to get the glGetString function pointer instead of calling it by its prototype?

(If I understand correctly and the first glGetString call to get GL_VENDOR crashes)

That wouldn't explain the issue with glClearColor or glClear, though, right? :S

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Should be very easy to test, and it might, though I'm not sure I understand exactly what happens.

 

Does it always crash every time on the first glGetString if that call is there, and crashes on glClearColor instead if you comment out the glGetString?

Or do you  mean that it randomly crashes on some GL call somewhere, but sometimes executes glGetString and properly prints it before crashing on glClearColor?

 

If it always crashes on the first GL call whatever that may be when MakeCurrent returns true it seems likely it's something with the function not calling the proper driver.. though just a guess.

 

If it is random it seems more likely that some memory corruption leads to a crash at some random point in the future or something.

 

You might also want to check your std::cout as I believe glGetString returns unsigned byte pointers.. if that is the case then they won't print a string (though it shouldn't crash as they should just print an address instead.. but you could cast them to char* and see if something changes).

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Erik, I mean it crashes on the first OpenGL call. I'm going to look into it the mis-return of MakeCurrent, though I have no idea why that would be a problem :S

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Again, I suggest then to do glXGetProcAddress("glGetString") and checking so that the function pointer returned is not null, and if it isn't then calling through that instead of using the regular glGetString. (Provided glXGetProcAddress doesn't crash instead, if it does, reinstall the driver).

And first maybe try glXMakeContextCurrent instead of glXMakeCurrent.

Edited by Erik Rufelt

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Also I see now that you don't seem to actually check that 'context' returned isn't NULL when you create it. MakeCurrent could return True on a NULL context by just disabling the thread context.

Edited by Erik Rufelt

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Tried this, didn't call. It seems literally everything is running fine until the gl calls -_-
if (context == NULL) {
std::cout << "Null Context!" << std::endl;
exit (0);
}

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And if you meant replacing 

    if (!glXMakeCurrent(display, window, context))

 

with this:

 

    if (!glXMakeContextCurrent(display, window, window, context))

 

Then it didn't work :/

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Try printing it like std::cout << "context = " << std::hex << (void*)context..

Also the function pointers are not supposed to be true, if they just return that then you probably have a null context..

Print them the same.. << std::hex << (void*)glXGetProcAddress("glGetString").. it should print a proper pointer and not '1' or anything like that..

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Where did you call that glXGetProcAddress? Make sure it works in the same place as where you do the call to glClear.

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Where did you call that glXGetProcAddress? Make sure it works in the same place as where you do the call to glClear.

Sponji I put it right before either the glGetString or the glClear, depending on the one I was testing.

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Yeah, but those functions work? Try it where it crashes, because then it would probably give you null pointers, which would mean that the context is not made current.

 

Edit: Or what, do those work or not? Not sure if you've made that clear yet. Do the gl functions work right after creating the context?

Edited by Sponji

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Yeah, but those functions work? Try it where it crashes, because then it would probably give you null pointers, which would mean that the context is not made current.

 

Edit: Or what, do those work or not? Not sure if you've made that clear yet. Do the gl functions work right after creating the context?

 

Try printing it like std::cout << "context = " << std::hex << (void*)context..

Also the function pointers are not supposed to be true, if they just return that then you probably have a null context..

Print them the same.. << std::hex << (void*)glXGetProcAddress("glGetString").. it should print a proper pointer and not '1' or anything like that..

Sponji and Erik, context, and the glXGetProcAdress of both glGetString and glClear all return proper hex values. When I said they return true, I meant I put them in an if condition and they returned a value, but I did as Erik said, to no avail. Thanks again guys! Do you have any other suggestions? This really makes no sense and I'm starting to miss Win32 of all things! XD

 

EDIT: Sponji, they still cause segfaults. I'm saying when I write this:

 

    ...

    std::cout << "Result = " << std::hex << (void*)glXGetProcAddress((const GLubyte *)"glClear") << std::endl;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    ...

 

...it still crashes :/

 

Edit 2: I tried an iteration of this earlier today without any of the other code and it worked, but NO code is being called before this :/ 

Edited by KarimIO

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Try something like this, as first GL call instead, see if it prints something or if that also crashes:

typedef const GLubyte *(APIENTRYP PFNGLGETSTRINGPROC) (GLenum name);

...

PFNGLGETSTRINGPROC pfnglGetString = (PFNGLGETSTRINGPROC)glXGetProcAddress((const GLubyte*)"glGetString");
std::cout << (const char*)pfnglGetString(GL_VENDOR) << std::endl;

(Btw did you reboot after you installed the driver?)

Try running some OpenGL demo app or something.

Edited by Erik Rufelt

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Strangely enough, (const char*)pfnglGetString(GL_VENDOR) doesn't return anything.

 

And by the way, I didn't install the driver today, I installed it a while ago. It's updated though.

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It doesn't crash?
Try using the pfnglgetString function pointer to get the other strings as well, and check the return values for null as well to make sure any crash is actually in the function call and not in using the return value. And then get glClearColor and glClear through glXGetProcAddress as well.

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It doesn't crash?
Try using the pfnglgetString function pointer to get the other strings as well, and check the return values for null as well to make sure any crash is actually in the function call and not in using the return value. And then get glClearColor and glClear through glXGetProcAddress as well.

Okay, it works,apparently, but I can't exactly just use 

 
PFNGLCLEAR pfnglClear = (PFNGLCLEAR)glXGetProcAddress((const GLubyte*)"glClear");

pfnglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 

instead of glClear O_O Any ideas?

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Okay, it works,apparently, but I can't exactly just use

 

Sure you can..

If you're going to use GL3 you will have to load a whole bunch of functions anyway. GLEW loads all of them for you, so if you use that perhaps it will fix everything for you.

 

 

Otherwise, try downing the context version to 2.0 or set the compatibility profile or something and see if that works, or just use the "old method" to create the context from before the whole context with attribs thing in GL3...

If you want some of the reasonably new GL functionality get glcorearb.h from the OpenGL registry and it has the function pointer definitions already so you don't have to typedef them yourself for the older functions.

Anyway.. strongly recommend getting GLEW to avoid the hassle.

Edited by Erik Rufelt

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Yeah I actually JUST connected the InitializeWindow to the rest of my game engine. It works now, though I'm getting some crazy junk for the mouse pointer so the game is spinning like crazy XD And yeah, I moved from GLEW to GL3W long ago because GLEW is outdated and requires Experimental :/

 

Thanks again to both of you. I can't thank you enough, really!!

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      GL_ARB_gl_spirv and GL_ARB_spirv_extensions to standardize SPIR-V support for OpenGL GL_ARB_indirect_parameters and GL_ARB_shader_draw_parameters for reducing the CPU overhead associated with rendering batches of geometry GL_ARB_pipeline_statistics_query and GL_ARB_transform_feedback_overflow_querystandardize OpenGL support for features available in Direct3D GL_ARB_texture_filter_anisotropic (based on GL_EXT_texture_filter_anisotropic) brings previously IP encumbered functionality into OpenGL to improve the visual quality of textured scenes GL_ARB_polygon_offset_clamp (based on GL_EXT_polygon_offset_clamp) suppresses a common visual artifact known as a “light leak” associated with rendering shadows GL_ARB_shader_atomic_counter_ops and GL_ARB_shader_group_vote add shader intrinsics supported by all desktop vendors to improve functionality and performance GL_KHR_no_error reduces driver overhead by allowing the application to indicate that it expects error-free operation so errors need not be generated In addition to the above features being added to OpenGL 4.6, the following are being released as extensions:
      GL_KHR_parallel_shader_compile allows applications to launch multiple shader compile threads to improve shader compile throughput WGL_ARB_create_context_no_error and GXL_ARB_create_context_no_error allow no error contexts to be created with WGL or GLX that support the GL_KHR_no_error extension “I’m proud to announce OpenGL 4.6 as the most feature-rich version of OpenGL yet. We've brought together the most popular, widely-supported extensions into a new core specification to give OpenGL developers and end users an improved baseline feature set. This includes resolving previous intellectual property roadblocks to bringing anisotropic texture filtering and polygon offset clamping into the core specification to enable widespread implementation and usage,” said Piers Daniell, chair of the OpenGL Working Group at Khronos. “The OpenGL working group will continue to respond to market needs and work with GPU vendors to ensure OpenGL remains a viable and evolving graphics API for all its customers and users across many vital industries.“
      The OpenGL 4.6 specification can be found at https://khronos.org/registry/OpenGL/index_gl.php. The GLSL to SPIR-V compiler glslang has been updated with GLSL 4.60 support, and can be found at https://github.com/KhronosGroup/glslang.
      Sophisticated graphics applications will also benefit from a set of newly released extensions for both OpenGL and OpenGL ES to enable interoperability with Vulkan and Direct3D. These extensions are named:
      GL_EXT_memory_object GL_EXT_memory_object_fd GL_EXT_memory_object_win32 GL_EXT_semaphore GL_EXT_semaphore_fd GL_EXT_semaphore_win32 GL_EXT_win32_keyed_mutex They can be found at: https://khronos.org/registry/OpenGL/index_gl.php
      Industry Support for OpenGL 4.6
      “With OpenGL 4.6 our customers have an improved set of core features available on our full range of OpenGL 4.x capable GPUs. These features provide improved rendering quality, performance and functionality. As the graphics industry’s most popular API, we fully support OpenGL and will continue to work closely with the Khronos Group on the development of new OpenGL specifications and extensions for our customers. NVIDIA has released beta OpenGL 4.6 drivers today at https://developer.nvidia.com/opengl-driver so developers can use these new features right away,” said Bob Pette, vice president, Professional Graphics at NVIDIA.
      "OpenGL 4.6 will be the first OpenGL release where conformant open source implementations based on the Mesa project will be deliverable in a reasonable timeframe after release. The open sourcing of the OpenGL conformance test suite and ongoing work between Khronos and X.org will also allow for non-vendor led open source implementations to achieve conformance in the near future," said David Airlie, senior principal engineer at Red Hat, and developer on Mesa/X.org projects.

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    • By _OskaR
      Hi,
      I have an OpenGL application but without possibility to wite own shaders.
      I need to perform small VS modification - is possible to do it in an alternative way? Do we have apps or driver modifictions which will catch the shader sent to GPU and override it?
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