Question

I have a library, which is engaged in rendering on opengl and prinimaet streams from the network.

I write under a poppy, but plans to use on linux

so the window is created for objective c
I start drawing in a separate thread in the other receiving and decoding the data.

I crash bug (EXT_BAD_ACCESS) on methods of opengl, even if I use them only in a single thread.

my code
main glut:

int main(int argc, const char * argv[]){
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
int win = glutGetWindow();
glutInitWindowSize(800, 600);
glutCreateWindow("OpenGL lesson 1");
client_init(1280, 720, win, "192.168.0.98", 8000, 2222);
return 0;

}

or objective c

- (id)initWithFrame:(NSRect)frameRect pixelFormat:(NSOpenGLPixelFormat*)format{
self = [super initWithFrame:frameRect];
if (self != nil) {
    NSOpenGLPixelFormatAttribute attributes[] = {

        NSOpenGLPFANoRecovery,
        NSOpenGLPFAFullScreen,
        NSOpenGLPFAScreenMask,
        CGDisplayIDToOpenGLDisplayMask(kCGDirectMainDisplay),
        (NSOpenGLPixelFormatAttribute) 0
    };
    _pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes];
    if (!_pixelFormat)
    {
        return nil;
    }
    //_pixelFormat   = [format retain];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(_surfaceNeedsUpdate:)
                                                 name:NSViewGlobalFrameDidChangeNotification
                                               object:self];
    _openGLContext = [self openGLContext];
    client_init(1280, 720, win, "192.168.0.98", 8000, 2222);
}
return self;

}

client_init code

    // pthread_create(&posixThreadID, NULL, (void*(*)(void*))ShowThread, dh_tmp);
pthread_create(&posixThreadID, NULL, (void*(*)(void*))ShowThread, NULL);

void* ShowThread(struct drawhandle * dh){

        //glViewport(0, 0, dh->swidth, dh->sheight);//EXT_BAD_ACCESS
        glViewport(0, 0, 1280, 720);//EXT_BAD_ACCESS

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        //gluOrtho2D(0, dh->swidth, 0, dh->sheight);
        gluOrtho2D(0, 1280, 0, 720);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

    ...
        return 0;
    }

I think the problem is? that uncreated context opengl.

How to create it in macos / linux?

Answer 1

This thread has no current OpenGL context. Even if you did create a context earlier in the program (not visible in your snippet), it will not be current in the thread you launch.

An OpenGL context is always, with no exceptions, “current” for exactly one thread at a time. By default this is the thread that created the context. Any thread calling OpenGL must be made “current” first.

You must either create the context in this thread, or call glXMakeCurrent (Unix/Linux) or aglMakeCurrent (Mac) or wglMakeCurrent (Windows) inside ShowThread (before doing anything else related to OpenGL).

(probably not the reason for the crash, though… see datenwolf’s answer for the likely reason of the crash — nevertheless it’s wrong)`