Bool fbCreateWindow(WindowPtr pWin) {
    // 初始化窗口画布PixMapPtr，非根模式下由fbCreatePixmap，而根模式由screen->CreatePixmap链式回调创建
    dixSetPrivate(&pWin->devPrivates, fbGetWinPrivateKey(pWin), fbGetScreenPixmap(pWin->drawable.pScreen));
    return TRUE;
}
 
Bool compCreateWindow(WindowPtr pWin) {
    ScreenPtr pScreen = pWin->drawable.pScreen;
    Bool ret = fbCreateWindow (pWin);
    // 条件不满足，根窗口没有父窗口
    if (pWin->parent && ret) {
        CompSubwindowsPtr csw = GetCompSubwindows(pWin->parent);
        CompClientWindowPtr ccw;
        PixmapPtr parent_pixmap = (*pScreen->GetWindowPixmap)(pWin->parent);
        PixmapPtr window_pixmap = (*pScreen->GetWindowPixmap)(pWin);
 
        if (window_pixmap != parent_pixmap)
            (*pScreen->SetWindowPixmap) (pWin, parent_pixmap);
        if (csw)
            for (ccw = csw->clients; ccw; ccw = ccw->next)
                compRedirectWindow(clients[CLIENT_ID(ccw->id)],
                                   pWin, ccw->update);
        if (compImplicitRedirect(pWin, pWin->parent))
            compRedirectWindow(serverClient, pWin, CompositeRedirectAutomatic);
    }
    return ret;
}
 
static Bool xwl_glamor_create_window(WindowPtr window) {
    // 条件不满足，根窗口没有父窗口
    if (window->parent)
        xwl_avoid_implicit_redirect(window);
    return compCreateWindow (window);
}

// 桩函数，啥都不做
Bool fbPositionWindow(WindowPtr pWin, int x, int y){ return TRUE; }
 
Bool
compPositionWindow(WindowPtr pWin, int x, int y)
{
    ScreenPtr pScreen = pWin->drawable.pScreen;
    Bool ret = TRUE;
    // 根窗口不满足该条件
    if (pWin->redirectDraw != RedirectDrawNone) {
        PixmapPtr pPixmap = (*pScreen->GetWindowPixmap) (pWin);
        int bw = wBorderWidth(pWin);
        int nx = pWin->drawable.x - bw;
        int ny = pWin->drawable.y - bw;
 
        if (pPixmap->screen_x != nx || pPixmap->screen_y != ny) {
            pPixmap->screen_x = nx;
            pPixmap->screen_y = ny;
            pPixmap->drawable.serialNumber = NEXT_SERIAL_NUMBER;
        }
    }
 
    if (!fbPositionWindow(pWin, x, y))
        ret = FALSE;
    // 更新重叠窗口，此时根窗口此时无重叠窗口
    if (updateOverlayWindow(pScreen) != Success)
        ret = FALSE;
    return ret;
}

// mask = (CWBorderPixel | CWCursor || CWBackingStore | CWBackPixel)
// 处理pixmap，而根窗口为pixel。
Bool fbChangeWindowAttributes(WindowPtr pWin, unsigned long mask) {
    if (mask & CWBackPixmap) {
        if (pWin->backgroundState == BackgroundPixmap)
            fbFixupWindowPixmap(&pWin->drawable, &pWin->background.pixmap);
    }
    if (mask & CWBorderPixmap) {
        if (pWin->borderIsPixel == FALSE)
            fbFixupWindowPixmap(&pWin->drawable, &pWin->border.pixmap);
    }
    return TRUE;
}
// 处理后端存储，而根窗口不支持后端存储
static Bool compChangeWindowAttributes(WindowPtr pWin, unsigned long mask){
    ScreenPtr pScreen = pWin->drawable.pScreen;
    Bool ret = fbChangeWindowAttributes(pWin, mask);
    // 根窗口的backingStoreSupport为WhenMapped，条件满足，但backingStore = NotUseful，compCheckBackingStore啥事也不做
    if (ret && (mask & CWBackingStore) && pScreen->backingStoreSupport != NotUseful)
        compCheckBackingStore(pWin);
    return ret;
}
 
Bool xwl_change_window_attributes(WindowPtr window, unsigned long mask)
{
    ScreenPtr screen = window->drawable.pScreen;
    struct xwl_screen *xwl_screen = xwl_screen_get(screen);
    OtherClients *others;
    Bool ret = compChangeWindowAttributes(window, mask);
    if (window != screen->root || !(mask & CWEventMask))
        return ret;
 
    // 查找窗口管理器客户端，窗口管理器将其mask设置为 SubstructureRedirectMask
    for (others = wOtherClients(window); others; others = others->next) {
        if (others->mask & (SubstructureRedirectMask | ResizeRedirectMask))
            xwl_screen->wm_client_id = CLIENT_ID(others->resource);
    }
    return ret;
}

Bool fbRealizeWindow(WindowPtr pWindow) { return TRUE; }
 
Bool compRealizeWindow(WindowPtr pWin) {
    compCheckRedirect(pWin);
   fbRealizeWindow(pWin);
    return TRUE;
}
 
Bool xwl_realize_window(WindowPtr window){
    ScreenPtr screen = window->drawable.pScreen;
    CompScreenPtr comp_screen = GetCompScreen(screen);
    struct xwl_screen *xwl_screen = xwl_screen_get(screen);
    ret = compRealizeWindow(window);
    if (xwl_screen->rootless) {
        /* We do not want the COW to be mapped when rootless in Xwayland */
        if (window == comp_screen->pOverlayWin) {
            window->mapped = FALSE;
            return TRUE;
        }
        // 初始化根窗口空间，其它空间清空
        if (!window->parent) {
            BoxRec box = { 0, 0, xwl_screen->width, xwl_screen->height };
            RegionReset(&window->winSize, &box);
            RegionNull(&window->clipList);
            RegionNull(&window->borderClip);
        }
    }
    // 条件不满足，根窗口的父窗口为空，只有顶层窗口满足该条件
    if (xwl_screen->rootless ? (window->drawable.class == InputOutput && window->parent == window->drawable.pScreen->root) : !window->parent) {
        if (!register_damage(window)) return FALSE;
    }
    // 该函数对根窗口不做任何处理，其redirectDraw = RedirectDrawNone
    return ensure_surface_for_window(window);
}