xcb: Use a placeholder QScreen when there are no outputs connected

If no screens are available, windows could disappear, could stop rendering
graphics, or the application could crash.  This is a real use case in several
scenarios: with x11vnc, when all monitors are physically disconnected from a
desktop machine, or in some cases even when the monitor sleeps.  Now when the
last screen is disconnected, it is transformed into a fake screen.  When a
physical screen appears, the fake QScreen is transformed into a representation
of the physical screen.  Every virtual desktop has its own fake screen, and
primary screens must belong to the primary virtual desktop. It fixes updating
screen geometry on temporarily disabled screens in the middle of the mode
switch.

Expected results: Windows don't disappear, the application doesn't
crash, and QMenu is displayed on the appropriate screen.

This reverts patch 51ada7734ad780178ecced11e0dff454dfc2e5f2

Change-Id: I6e8eb682b0c8425d08ffdaecbd4c6c7700c914b4
Task-number: QTBUG-42985
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbscreen.h b/src/plugins/platforms/xcb/qxcbscreen.h
index c68c290791..79620f40ec 100644
--- a/src/plugins/platforms/xcb/qxcbscreen.h
+++ b/src/plugins/platforms/xcb/qxcbscreen.h
@@ -72,6 +72,7 @@ public:
     void setScreens(QList<QPlatformScreen *> sl) { m_screens = sl; }
     void removeScreen(QPlatformScreen *s) { m_screens.removeOne(s); }
     void addScreen(QPlatformScreen *s);
+    void setPrimaryScreen(QPlatformScreen *s);
 
     QXcbXSettings *xSettings() const;
 
@@ -101,10 +102,11 @@ class Q_XCB_EXPORT QXcbScreen : public QXcbObject, public QPlatformScreen
 {
 public:
     QXcbScreen(QXcbConnection *connection, QXcbVirtualDesktop *virtualDesktop,
-               xcb_randr_output_t outputId, xcb_randr_get_output_info_reply_t *output,
-               QString outputName);
+               xcb_randr_output_t outputId, xcb_randr_get_output_info_reply_t *outputInfo);
     ~QXcbScreen();
 
+    QString getOutputName(xcb_randr_get_output_info_reply_t *outputInfo);
+
     QPixmap grabWindow(WId window, int x, int y, int width, int height) const Q_DECL_OVERRIDE;
 
     QWindow *topLevelAt(const QPoint &point) const Q_DECL_OVERRIDE;
@@ -137,6 +139,10 @@ public:
     xcb_randr_crtc_t crtc() const { return m_crtc; }
     xcb_randr_mode_t mode() const { return m_mode; }
 
+    void setOutput(xcb_randr_output_t outputId,
+                   xcb_randr_get_output_info_reply_t *outputInfo);
+    void setCrtc(xcb_randr_crtc_t crtc) { m_crtc = crtc; }
+
     void windowShown(QXcbWindow *window);
     QString windowManagerName() const { return m_windowManagerName; }
     bool syncRequestSupported() const { return m_syncRequestSupported; }