Darwin: Patch to avert (some) damage / rootless crashes, courtesy of Ken Thomases

(cherry picked from commit 148a87ff20aa5e7a6d839610aa14fa1a31505c4a)

miext/rootless/rootless.h

@@ -66,7 +66,6 @@ typedef struct _RootlessWindowRec {
     int bytesPerRow;
 
     PixmapPtr pixmap;
-    PixmapPtr oldPixmap;
 
 #ifdef ROOTLESS_TRACK_DAMAGE
     RegionRec damage;

miext/rootless/rootlessCommon.c

@@ -172,9 +172,25 @@ void RootlessStartDrawing(WindowPtr pWindow)
         winRec->is_drawing = TRUE;
     }
 
-    winRec->oldPixmap = pScreen->GetWindowPixmap(pWindow);
+    PixmapPtr curPixmap = pScreen->GetWindowPixmap(pWindow);
+    if (curPixmap == winRec->pixmap)
+    {
+        RL_DEBUG_MSG("Window %p already has winRec->pixmap %p; not pushing\n", pWindow, winRec->pixmap);
+    }
+    else
+    {
+        PixmapPtr oldPixmap = pWindow->devPrivates[rootlessWindowOldPixmapPrivateIndex].ptr;
+        if (oldPixmap != NULL)
+        {
+            if (oldPixmap == curPixmap)
+                RL_DEBUG_MSG("Window %p's curPixmap %p is the same as its oldPixmap; strange\n", pWindow, curPixmap);
+            else
+                RL_DEBUG_MSG("Window %p's existing oldPixmap %p being lost!\n", pWindow, oldPixmap);
+        }
+        pWindow->devPrivates[rootlessWindowOldPixmapPrivateIndex].ptr = curPixmap;
         pScreen->SetWindowPixmap(pWindow, winRec->pixmap);
     }
+}
 
 
 /*
@@ -182,6 +198,29 @@ void RootlessStartDrawing(WindowPtr pWindow)
  *  Stop drawing to a window's backing buffer. If flush is true,
  *  damaged regions are flushed to the screen.
  */
+static int RestorePreDrawingPixmapVisitor(WindowPtr pWindow, pointer data)
+{
+    RootlessWindowRec *winRec = (RootlessWindowRec*)data;
+    ScreenPtr pScreen = pWindow->drawable.pScreen;
+    PixmapPtr exPixmap = pScreen->GetWindowPixmap(pWindow);
+    PixmapPtr oldPixmap = pWindow->devPrivates[rootlessWindowOldPixmapPrivateIndex].ptr;
+    if (oldPixmap == NULL)
+    {
+        if (exPixmap == winRec->pixmap)
+            RL_DEBUG_MSG("Window %p appears to be in drawing mode (ex-pixmap %p equals winRec->pixmap, which is being freed) but has no oldPixmap!\n", pWindow, exPixmap);
+    }
+    else
+    {
+        if (exPixmap != winRec->pixmap)
+            RL_DEBUG_MSG("Window %p appears to be in drawing mode (oldPixmap %p) but ex-pixmap %p not winRec->pixmap %p!\n", pWindow, oldPixmap, exPixmap, winRec->pixmap);
+        if (oldPixmap == winRec->pixmap)
+            RL_DEBUG_MSG("Window %p's oldPixmap %p is winRec->pixmap, which has just been freed!\n", pWindow, oldPixmap);
+        pScreen->SetWindowPixmap(pWindow, oldPixmap);
+        pWindow->devPrivates[rootlessWindowOldPixmapPrivateIndex].ptr = NULL;
+    }
+    return WT_WALKCHILDREN;
+}
+
 void RootlessStopDrawing(WindowPtr pWindow, Bool flush)
 {
     ScreenPtr pScreen = pWindow->drawable.pScreen;
@@ -198,7 +237,7 @@ void RootlessStopDrawing(WindowPtr pWindow, Bool flush)
         SCREENREC(pScreen)->imp->StopDrawing(winRec->wid, flush);
 
         FreeScratchPixmapHeader(winRec->pixmap);
-        pScreen->SetWindowPixmap(pWindow, winRec->oldPixmap);
+        TraverseTree(top, RestorePreDrawingPixmapVisitor, (pointer)winRec);
         winRec->pixmap = NULL;
 
         winRec->is_drawing = FALSE;

miext/rootless/rootlessCommon.h

@@ -60,6 +60,7 @@
 extern int rootlessGCPrivateIndex;
 extern int rootlessScreenPrivateIndex;
 extern int rootlessWindowPrivateIndex;
+extern int rootlessWindowOldPixmapPrivateIndex;
 
 
 // RootlessGCRec: private per-gc data

miext/rootless/rootlessScreen.c

@@ -65,6 +65,7 @@ extern Bool RootlessCreateGC(GCPtr pGC);
 int rootlessGCPrivateIndex = -1;
 int rootlessScreenPrivateIndex = -1;
 int rootlessWindowPrivateIndex = -1;
+int rootlessWindowOldPixmapPrivateIndex = -1;
 
 
 /*
@@ -618,6 +619,8 @@ RootlessAllocatePrivates(ScreenPtr pScreen)
         if (rootlessGCPrivateIndex == -1) return FALSE;
         rootlessWindowPrivateIndex = AllocateWindowPrivateIndex();
         if (rootlessWindowPrivateIndex == -1) return FALSE;
+        rootlessWindowOldPixmapPrivateIndex = AllocateWindowPrivateIndex();
+        if (rootlessWindowOldPixmapPrivateIndex == -1) return FALSE;
         rootlessGeneration = serverGeneration;
     }
 
@@ -627,6 +630,8 @@ RootlessAllocatePrivates(ScreenPtr pScreen)
         return FALSE;
     if (!AllocateWindowPrivate(pScreen, rootlessWindowPrivateIndex, 0))
         return FALSE;
+    if (!AllocateWindowPrivate(pScreen, rootlessWindowOldPixmapPrivateIndex, 0))
+        return FALSE;
 
     s = xalloc(sizeof(RootlessScreenRec));
     if (! s) return FALSE;

miext/rootless/rootlessWindow.c

@@ -198,6 +198,7 @@ RootlessCreateWindow(WindowPtr pWin)
     RegionRec saveRoot;
 
     WINREC(pWin) = NULL;
+    pWin->devPrivates[rootlessWindowOldPixmapPrivateIndex].ptr = NULL;
 
     SCREEN_UNWRAP(pWin->drawable.pScreen, CreateWindow);