dix: Add hybrid full-size/empty-clip mode to SetRootClip

216bdbc735 removed the SetRootClip call in the XWayland output-hotplug
handler when running rootless (e.g. as a part of Weston/Mutter), since
the root window has no storage, so generating exposures will result in
writes to invalid memory.

Unfortunately, preventing the segfault also breaks sprite confinement.
SetRootClip updates winSize and borderSize for the root window, which
when combined with RRScreenSizeChanged calling ScreenRestructured,
generates a new sprite-confinment area to update it to the whole screen.

Removing this call results in the window geometry being reported
correctly, but winSize/borderSize never changing from their values at
startup, i.e. out of sync with the root window geometry / screen
information in the connection info / XRandR.

This patch introduces a hybrid mode, where we update winSize and
borderSize for the root window, enabling sprite confinement to work
correctly, but keep the clip emptied so exposures are never generated.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Tested-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/include/window.h b/include/window.h
index f13ed5115..7a22febf8 100644
--- a/include/window.h
+++ b/include/window.h
@@ -72,6 +72,12 @@ struct _Cursor;
 typedef struct _BackingStore *BackingStorePtr;
 typedef struct _Window *WindowPtr;
 
+enum RootClipMode {
+    ROOT_CLIP_NONE = 0, /**< resize the root window to 0x0 */
+    ROOT_CLIP_FULL = 1, /**< resize the root window to fit screen */
+    ROOT_CLIP_INPUT_ONLY = 2, /**< as above, but no rendering to screen */
+};
+
 typedef int (*VisitWindowProcPtr) (WindowPtr pWin,
                                    void *data);
 
@@ -221,7 +227,7 @@ extern _X_EXPORT RegionPtr CreateBoundingShape(WindowPtr /* pWin */ );
 
 extern _X_EXPORT RegionPtr CreateClipShape(WindowPtr /* pWin */ );
 
-extern _X_EXPORT void SetRootClip(ScreenPtr pScreen, Bool enable);
+extern _X_EXPORT void SetRootClip(ScreenPtr pScreen, int enable);
 extern _X_EXPORT void PrintWindowTree(void);
 extern _X_EXPORT void PrintPassiveGrabs(void);