Index: /trunk/src/VBox/Additions/x11/vboxvideo/setmode.c
===================================================================
--- /trunk/src/VBox/Additions/x11/vboxvideo/setmode.c	(revision 55236)
+++ /trunk/src/VBox/Additions/x11/vboxvideo/setmode.c	(revision 55237)
@@ -71,4 +71,23 @@
 # include <unistd.h>
 #endif
+
+/** Clear the virtual framebuffer in VRAM.  Optionally also clear up to the
+ * size of a new framebuffer.  Framebuffer sizes larger than available VRAM
+ * be treated as zero and passed over. */
+void vbvxClearVRAM(ScrnInfoPtr pScrn, size_t cbOldSize, size_t cbNewSize)
+{
+    VBOXPtr pVBox = VBOXGetRec(pScrn);
+
+    /* Assume 32BPP - this is just a sanity test. */
+    VBVXASSERT(   cbOldSize / 4 <= VBOX_VIDEO_MAX_VIRTUAL * VBOX_VIDEO_MAX_VIRTUAL
+               && cbNewSize / 4 <= VBOX_VIDEO_MAX_VIRTUAL * VBOX_VIDEO_MAX_VIRTUAL,
+               ("cbOldSize=%llu cbNewSize=%llu, max=%u.\n", (unsigned long long)cbOldSize, (unsigned long long)cbNewSize,
+                VBOX_VIDEO_MAX_VIRTUAL * VBOX_VIDEO_MAX_VIRTUAL));
+    if (cbOldSize > (size_t)pVBox->cbFBMax)
+        cbOldSize = pVBox->cbFBMax;
+    if (cbNewSize > (size_t)pVBox->cbFBMax)
+        cbNewSize = pVBox->cbFBMax;
+    memset(pVBox->base, 0, max(cbOldSize, cbNewSize));
+}
 
 /** Clear the virtual framebuffer in VRAM.  Optionally also clear up to the
Index: /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.h
===================================================================
--- /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.h	(revision 55236)
+++ /trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.h	(revision 55237)
@@ -257,4 +257,5 @@
 
 /* setmode.c */
+extern void vbvxClearVRAM(ScrnInfoPtr pScrn, size_t cbOldSize, size_t cbNewSize);
 extern void vbvxSetSolarisMouseRange(int width, int height);