Add support for notifying clients about pointer movements

This change adds support for the VMware Mouse Position
pseudo-encoding[1], which is used to notify VNC clients when X11 clients
call `XWarpPointer()`[2]. This function is called by SDL (and other
similar libraries)  when they detect that the server does not support
native relative motion, like some RFB clients.

With this, RFB clients can choose to adjust the local cursor position
under certain circumstances to match what the server has set. For
instance, if pointer lock has been enabled on the client's machine and
the cursor is not being drawn locally, the local position of the cursor
is irrelevant, so the RFB client can use what the server sends as the
canonical absolute position of the cursor. This ultimately enables the
possibility of games (especially FPS games) to behave how users expect
(if the clients implement the corresponding change).

Part of: #619

1: https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#vmware-cursor-position-pseudo-encoding
2: https://tronche.com/gui/x/xlib/input/XWarpPointer.html
3: https://hg.libsdl.org/SDL/file/28e3b60e2131/src/events/SDL_mouse.c#l804

unix/xserver/hw/vnc/XserverDesktop.cc

@@ -241,6 +241,15 @@ void XserverDesktop::setCursor(int width, int height, int hotX, int hotY,
   delete [] cursorData;
 }
 
+void XserverDesktop::setCursorPos(int x, int y, bool warped)
+{
+  try {
+    server->setCursorPos(Point(x, y), warped);
+  } catch (rdr::Exception& e) {
+    vlog.error("XserverDesktop::setCursorPos: %s",e.str());
+  }
+}
+
 void XserverDesktop::add_changed(const rfb::Region &region)
 {
   try {
@@ -358,7 +367,7 @@ void XserverDesktop::blockHandler(int* timeout)
     if (oldCursorPos.x != cursorX || oldCursorPos.y != cursorY) {
       oldCursorPos.x = cursorX;
       oldCursorPos.y = cursorY;
-      server->setCursorPos(oldCursorPos);
+      server->setCursorPos(oldCursorPos, false);
     }
 
     // Trigger timers and check when the next will expire

unix/xserver/hw/vnc/XserverDesktop.h

@@ -66,6 +66,7 @@ public:
   void setDesktopName(const char* name);
   void setCursor(int width, int height, int hotX, int hotY,
                  const unsigned char *rgbaData);
+  void setCursorPos(int x, int y, bool warped);
   void add_changed(const rfb::Region &region);
   void add_copied(const rfb::Region &dest, const rfb::Point &delta);
   void handleSocketEvent(int fd, bool read, bool write);

unix/xserver/hw/vnc/vncExtInit.cc

@@ -418,6 +418,11 @@ void vncSetCursor(int width, int height, int hotX, int hotY,
     desktop[scr]->setCursor(width, height, hotX, hotY, rgbaData);
 }
 
+void vncSetCursorPos(int scrIdx, int x, int y)
+{
+  desktop[scrIdx]->setCursorPos(x, y, true);
+}
+
 void vncPreScreenResize(int scrIdx)
 {
   // We need to prevent the RFB core from accessing the framebuffer

unix/xserver/hw/vnc/vncExtInit.h

@@ -86,6 +86,7 @@ void vncAddCopied(int scrIdx, const struct UpdateRect *extents,
 
 void vncSetCursor(int width, int height, int hotX, int hotY,
                   const unsigned char *rgbaData);
+void vncSetCursorPos(int scrIdx, int x, int y);
 
 void vncPreScreenResize(int scrIdx);
 void vncPostScreenResize(int scrIdx, int success, int width, int height);

unix/xserver/hw/vnc/vncHooks.c

@@ -65,6 +65,9 @@ typedef struct _vncHooksScreenRec {
   RestoreAreasProcPtr          RestoreAreas;
 #endif
   DisplayCursorProcPtr         DisplayCursor;
+#if XORG >= 119
+  CursorWarpedToProcPtr        CursorWarpedTo;
+#endif
   ScreenBlockHandlerProcPtr    BlockHandler;
 #ifdef RENDER
   CompositeProcPtr             Composite;
@@ -137,6 +140,12 @@ static RegionPtr vncHooksRestoreAreas(WindowPtr pWin, RegionPtr prgnExposed);
 #endif
 static Bool vncHooksDisplayCursor(DeviceIntPtr pDev,
                                   ScreenPtr pScreen, CursorPtr cursor);
+#if XORG >= 119
+static void vncHooksCursorWarpedTo(DeviceIntPtr pDev,
+                                   ScreenPtr pScreen_, ClientPtr pClient,
+                                   WindowPtr pWindow, SpritePtr pSprite,
+                                   int x, int y);
+#endif
 #if XORG <= 112
 static void vncHooksBlockHandler(int i, pointer blockData, pointer pTimeout,
                                  pointer pReadmask);
@@ -316,6 +325,9 @@ int vncHooksInit(int scrIdx)
   wrap(vncHooksScreen, pScreen, RestoreAreas, vncHooksRestoreAreas);
 #endif
   wrap(vncHooksScreen, pScreen, DisplayCursor, vncHooksDisplayCursor);
+#if XORG >= 119
+  wrap(vncHooksScreen, pScreen, CursorWarpedTo, vncHooksCursorWarpedTo);
+#endif
   wrap(vncHooksScreen, pScreen, BlockHandler, vncHooksBlockHandler);
 #ifdef RENDER
   ps = GetPictureScreenIfSet(pScreen);
@@ -725,6 +737,20 @@ out:
   return ret;
 }
 
+// CursorWarpedTo - notify that the cursor was warped
+
+#if XORG >= 119
+static void vncHooksCursorWarpedTo(DeviceIntPtr pDev,
+                                   ScreenPtr pScreen_, ClientPtr pClient,
+                                   WindowPtr pWindow, SpritePtr pSprite,
+                                   int x, int y)
+{
+  SCREEN_PROLOGUE(pScreen_, CursorWarpedTo);
+  vncSetCursorPos(pScreen->myNum, x, y);
+  SCREEN_EPILOGUE(CursorWarpedTo);
+}
+#endif
+
 // BlockHandler - ignore any changes during the block handler - it's likely
 // these are just drawing the cursor.