如何在SDL

Question

有没有办法在不调用GLXContext的情况下获取与窗口关联的glXGetCurrentContext()？

Answer 1

Cast the SDL_GLContext you get from SDL_GL_CreateContext() to GLXContext：

SDL_GLContext
X11_GL_CreateContext(_THIS, SDL_Window * window)
{
    SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
    Display *display = data->videodata->display;
    int screen =
        ((SDL_DisplayData *) SDL_GetDisplayForWindow(window)->driverdata)->screen;
    XWindowAttributes xattr;
    XVisualInfo v, *vinfo;
    int n;
    GLXContext context = NULL, share_context;

    if (_this->gl_config.share_with_current_context) {
        share_context = (GLXContext)SDL_GL_GetCurrentContext();
    } else {
        share_context = NULL;
    }

    /* We do this to create a clean separation between X and GLX errors. */
    X11_XSync(display, False);
    errorHandlerOperation = "create GL context";
    errorBase = _this->gl_data->errorBase;
    errorCode = Success;
    handler = X11_XSetErrorHandler(X11_GL_ErrorHandler);
    X11_XGetWindowAttributes(display, data->xwindow, &xattr);
    v.screen = screen;
    v.visualid = X11_XVisualIDFromVisual(xattr.visual);
    vinfo = X11_XGetVisualInfo(display, VisualScreenMask | VisualIDMask, &v, &n);
    if (vinfo) {
        if (_this->gl_config.major_version < 3 &&
            _this->gl_config.profile_mask == 0 &&
            _this->gl_config.flags == 0) {
            /* Create legacy context */
            context =
                _this->gl_data->glXCreateContext(display, vinfo, share_context, True);
        } else {
            /* max 10 attributes plus terminator */
            int attribs[11] = {
                GLX_CONTEXT_MAJOR_VERSION_ARB,
                _this->gl_config.major_version,
                GLX_CONTEXT_MINOR_VERSION_ARB,
                _this->gl_config.minor_version,
                0
            };
            int iattr = 4;

            /* SDL profile bits match GLX profile bits */
            if( _this->gl_config.profile_mask != 0 ) {
                attribs[iattr++] = GLX_CONTEXT_PROFILE_MASK_ARB;
                attribs[iattr++] = _this->gl_config.profile_mask;
            }

            /* SDL flags match GLX flags */
            if( _this->gl_config.flags != 0 ) {
                attribs[iattr++] = GLX_CONTEXT_FLAGS_ARB;
                attribs[iattr++] = _this->gl_config.flags;
            }

            /* only set if glx extension is available */
            if( _this->gl_data->HAS_GLX_ARB_context_flush_control ) {
                attribs[iattr++] = GLX_CONTEXT_RELEASE_BEHAVIOR_ARB;
                attribs[iattr++] = 
                    _this->gl_config.release_behavior ? 
                    GLX_CONTEXT_RELEASE_BEHAVIOR_FLUSH_ARB : 
                    GLX_CONTEXT_RELEASE_BEHAVIOR_NONE_ARB;
            }

            attribs[iattr++] = 0;

            /* Get a pointer to the context creation function for GL 3.0 */
            if (!_this->gl_data->glXCreateContextAttribsARB) {
                SDL_SetError("OpenGL 3.0 and later are not supported by this system");
            } else {
                int glxAttribs[64];

                /* Create a GL 3.x context */
                GLXFBConfig *framebuffer_config = NULL;
                int fbcount = 0;

                X11_GL_GetAttributes(_this,display,screen,glxAttribs,64,SDL_TRUE);

                if (!_this->gl_data->glXChooseFBConfig
                    || !(framebuffer_config =
                        _this->gl_data->glXChooseFBConfig(display,
                                          DefaultScreen(display), glxAttribs,
                                          &fbcount))) {
                    SDL_SetError("No good framebuffers found. OpenGL 3.0 and later unavailable");
                } else {
                    context = _this->gl_data->glXCreateContextAttribsARB(display,
                                                    framebuffer_config[0],
                                                    share_context, True, attribs);
                }
            }
        }
        X11_XFree(vinfo);
    }
    X11_XSync(display, False);
    X11_XSetErrorHandler(handler);

    if (!context) {
        if (errorCode == Success) {
            SDL_SetError("Could not create GL context");
        }
        return NULL;
    }

    if (X11_GL_MakeCurrent(_this, window, context) < 0) {
        X11_GL_DeleteContext(_this, context);
        return NULL;
    }

    return context;
}

SDL2不会将上下文存储在任何地方。