使透明度不显示什么是在opengl与c++的窗口后面

我正在用c++在opengl中制作二维图像，并且我遇到了一个有趣的问题。每当我尝试在图像上绘制部分透明的多边形时，它都会使多边形所在的窗口本身部分透明。例如，当我运行程序(这是我不想要的)时，我可以看到我的窗口后面的任何东西(例如我的代码)。我还可以看到多边形后面的图像(我确实想要)。有什么方法可以关闭"透明窗口"行为吗?我把我认为相关的部分代码包括在下面:

glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // I have tried 1.0f for the alpha value too
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);
glHint(GL_POLYGON_SMOOTH_HINT, GL_NICEST);
glEnable(GL_BLEND);
glEnable(GL_LINE_SMOOTH);
glEnable(GL_POLYGON_SMOOTH);
glPolygonMode (GL_FRONT_AND_BACK, GL_FILL);
glHint(GL_POINT_SMOOTH_HINT, GL_FASTEST);
glDisable(GL_POINT_SMOOTH);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
    // other code to draw my opaque "background" object
    // Draw my partially transparent quad (note: this is where the window itself becomes partially transparent)
glBegin(GL_QUADS); // Begin drawing quads
    glColor4f(1.0,1.0,1.0,0.5); // Make a white quad with .5 alpha
    glVertex2f(-0.5, 0.5);
    glVertex2f(0.5, .05);
    glVertex2f(0.5, -0.5);
    glVertex2f(-0.5, -0.5);
    glEnd();

其他相关信息:

• 我正在运行CentOS 6
• 我对opengl相当陌生，并且在之前的开发人员之后正在编写代码，所以我可能会错过一些微不足道的东西
• 正在使用X Windows系统

下面是X窗口创建代码进一步调试，问题很可能在这里而不是上面的opengl代码。

/*  The simplest possible Linux OpenGL program? Maybe...
 Modification for creating a RGBA window (transparency with compositors)
 by Wolfgang 'datenwolf' Draxinger
 (c) 2002 by FTB. See me in comp.graphics.api.opengl
 (c) 2011 Wolfgang Draxinger. See me in comp.graphics.api.opengl and on StackOverflow
 License agreement: This source code is provided "as is". You
 can use this source code however you want for your own personal
 use. If you give this source code to anybody else then you must
 leave this message in it.
 --
 <___/>
 / O O 
 _____/  FTB.
 --
 datenwolf
 ------------------------------------------------------------------------*/
static void createTheWindow() {
XEvent event;
int x, y, attr_mask;
XSizeHints hints;
XWMHints *StartupState;
XTextProperty textprop;
XSetWindowAttributes attr;
static char *title = "Fix me";
/* Connect to the X server */
Xdisplay = XOpenDisplay(NULL);
if (!Xdisplay)
{
    fatalError("Couldn't connect to X servern");
}
Xscreen = DefaultScreen(Xdisplay);
Xroot = RootWindow(Xdisplay, Xscreen) ;
fbconfigs = glXChooseFBConfig(Xdisplay, Xscreen, VisData, &numfbconfigs);
for (int i = 0; i < numfbconfigs; i++)
{
    visual = (XVisualInfo_CPP*) glXGetVisualFromFBConfig(Xdisplay,
            fbconfigs[i]);
    if (!visual)
        continue;
    pictFormat = XRenderFindVisualFormat(Xdisplay, visual->visual);
    if (!pictFormat)
        continue;
    if (pictFormat->direct.alphaMask > 0)
    {
        fbconfig = fbconfigs[i];
        break;
    }
}
/* Create a colormap - only needed on some X clients, eg. IRIX */
cmap = XCreateColormap(Xdisplay, Xroot, visual->visual, AllocNone);
/* Prepare the attributes for our window */
attr.colormap = cmap;
attr.border_pixel = 0;
attr.event_mask = StructureNotifyMask | EnterWindowMask | LeaveWindowMask
        | ExposureMask | ButtonPressMask | ButtonReleaseMask
        | OwnerGrabButtonMask | KeyPressMask | KeyReleaseMask;
attr.background_pixmap = None;
attr_mask = CWBackPixmap | CWColormap | CWBorderPixel | CWEventMask; /* What's in the attr data */
width = DisplayWidth(Xdisplay, DefaultScreen(Xdisplay)) ;
height = DisplayHeight(Xdisplay, DefaultScreen(Xdisplay)) ;
x = width / 2, y = height / 2;
// x=0, y=10;
/* Create the window */
attr.do_not_propagate_mask = NoEventMask;
WindowHandle = XCreateWindow(Xdisplay, /* Screen */
Xroot, /* Parent */
x, y, width, height,/* Position */
1,/* Border */
visual->depth,/* Color depth*/
InputOutput,/* klass */
visual->visual,/* Visual */
attr_mask, &attr);/* Attributes*/
if (!WindowHandle)
{
    fatalError("Couldn't create the windown");
}
/* Configure it...  (ok, ok, this next bit isn't "minimal") */
textprop.value = (unsigned char*) title;
textprop.encoding = XA_STRING;
textprop.format = 8;
textprop.nitems = strlen(title);
hints.x = x;
hints.y = y;
hints.width = width;
hints.height = height;
hints.flags = USPosition | USSize;
StartupState = XAllocWMHints();
StartupState->initial_state = NormalState;
StartupState->flags = StateHint;
XSetWMProperties(Xdisplay, WindowHandle, &textprop, &textprop,/* Window title/icon title*/
NULL, 0,/* Argv[], argc for program*/
&hints, /* Start position/size*/
StartupState,/* Iconised/not flag   */
NULL);
XFree(StartupState);
/* Open it, wait for it to appear */
int event_base, error_base = 0;
XMapWindow(Xdisplay, WindowHandle);
//   }
XIfEvent(Xdisplay, &event, WaitForMapNotify, (char*) &WindowHandle);
/* Set the kill atom so we get a message when the user tries to close the window */
if ((del_atom = XInternAtom(Xdisplay, "WM_DELETE_WINDOW", 0)) != None)
{
    XSetWMProtocols(Xdisplay, WindowHandle, &del_atom, 1);
}
}

static int VisData[] = { GLX_RENDER_TYPE, GLX_RGBA_BIT, GLX_DRAWABLE_TYPE,
    GLX_WINDOW_BIT, GLX_DOUBLEBUFFER, True, GLX_RED_SIZE, 1, GLX_GREEN_SIZE,
    1, GLX_BLUE_SIZE, 1, GLX_ALPHA_SIZE, 1, GLX_DEPTH_SIZE, 1,
    None
};

下面是创建渲染上下文的地方:

static void createTheRenderContext() {
/* See if we can do OpenGL on this visual */
int dummy;
if (!glXQueryExtension(Xdisplay, &dummy, &dummy))
{
    fatalError("OpenGL not supported by X servern");
}
/* Create the OpenGL rendering context */
RenderContext = glXCreateNewContext(Xdisplay, fbconfig, GLX_RGBA_TYPE, 0,
        True);
if (!RenderContext)
{
    fatalError("Failed to create a GL contextn");
}
GLXWindowHandle = glXCreateWindow(Xdisplay, fbconfig, WindowHandle, NULL);
/* Make it current */
if (!glXMakeContextCurrent(Xdisplay, GLXWindowHandle, GLXWindowHandle,
        RenderContext))
{
    fatalError("glXMakeCurrent failed for windown");
}
}