I don't know if it's the best solution, but it surely works for me.
Binding the functions to local variables that we can use
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
typedef Bool (*glXMakeContextCurrentARBProc)(Display*, GLXDrawable, GLXDrawable, GLXContext);
static glXCreateContextAttribsARBProc glXCreateContextAttribsARB = NULL;
static glXMakeContextCurrentARBProc glXMakeContextCurrentARB = NULL;
Our objects as class properties:
Display *display;
GLXPbuffer pbuffer;
GLXContext openGLContext;
Setting up the context:
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );
glXMakeContextCurrentARB = (glXMakeContextCurrentARBProc) glXGetProcAddressARB( (const GLubyte *) "glXMakeContextCurrent");
display = XOpenDisplay(NULL);
if (display == NULL){
std::cout << "error getting the X display";
}
static int visualAttribs[] = {None};
int numberOfFrameBufferConfigurations;
GLXFBConfig *fbConfigs = glXChooseFBConfig(display, DefaultScreen(display), visualAttribs, &numberOfFrameBufferConfigurations);
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB ,3,
GLX_CONTEXT_MINOR_VERSION_ARB, 2,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_DEBUG_BIT_ARB,
GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
None
};
std::cout << "initialising context...";
this->openGLContext = glXCreateContextAttribsARB(display, fbConfigs[0], 0, True, context_attribs);
int pBufferAttribs[] = {
GLX_PBUFFER_WIDTH, (int)this->initialWidth,
GLX_PBUFFER_HEIGHT, (int)this->initialHeight,
None
};
this->pbuffer = glXCreatePbuffer(display, fbConfigs[0], pBufferAttribs);
XFree(fbConfigs);
XSync(display, False);
Using the context:
if(!glXMakeContextCurrent(display, pbuffer, pbuffer, openGLContext)){
std::cout << "error with content creation\n";
}else{
std::cout << "made a context the current context\n";
}
After that, one can use FBOs normally, as he would in any other occasion. Up to this day, my question is actually unanswered (if there is any better alternative), so I am just offering a solution that worked for me. Seems to me that GLX does not use the notion of pixel buffers the same way as OpenGL does, hence my confusion. The preferred way to render offscreen is FBOs, but for an OpenGL context to be created on Linux, a pixel buffer (the GLX kind) must be created. After that, using FBOs with the code I provided in the question will work as expected, the same way it does on OS X.