VNC: Add hooks to receive updates when the display is modified

graphics/vnc/server/Kconfig

@@ -8,6 +8,7 @@ menuconfig VNCSERVER
 	default n
 	depends on NET_TCP && !NX_LCDDRIVER && EXPERIMENTAL
 	select NET_TCP_READAHEAD
+	select NX_UPDATE
 	---help---
 		Enable support for a VNC Remote Frame Buffer (RFB) server.
 

graphics/vnc/server/vnc_fbdev.c

@@ -406,7 +406,7 @@ int up_fbinitialize(int display)
    */
 
   gvdbg("Starting the VNC server for display %d\n", display);
-  DEBUGASSERT(display >= 8 && display < RFB_MAX_DISPLAYS);
+  DEBUGASSERT(display >= 0 && display < RFB_MAX_DISPLAYS);
 
   (void)itoa(display, str, 10);
   argv[0] = str;
@@ -513,3 +513,54 @@ void up_fbuninitialize(int display)
   UNUSED(fbinfo);
 }
 
+/****************************************************************************
+ * Name: nx_notify_rectangle
+ *
+ * Description:
+ *   When CONFIG_NX_UPDATE=y, then the graphics system will callout to
+ *   inform some external module that the display has been updated.  This
+ *   would be useful in a couple for cases.
+ *
+ *   - When a serial LCD is used, but a framebuffer is used to access the
+ *     LCD.  In this case, the update callout can be used to refresh the
+ *     affected region of the display.
+ *
+ *   - When VNC is enabled.  This is case, this callout is necessary to
+ *     update the remote frame buffer to match the local framebuffer.
+ *
+ * When this feature is enabled, some external logic must provide this
+ * interface.  This is the function that will handle the notification.  It
+ * receives the rectangular region that was updated on the provided plane.
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_NX_UPDATE
+void nx_notify_rectangle(FAR NX_PLANEINFOTYPE *pinfo,
+                         FAR const struct nxgl_rect_s *rect)
+{
+  FAR struct vnc_session_s *session;
+  int ret;
+
+  DEBUGASSERT(pinfo != NULL && rect != NULL);
+
+  /* Recover the session informatin from the display number in the planeinfo
+   * structure.
+   */
+
+  DEBUGASSERT(pinfo->display >= 0 && pinfo->display < RFB_MAX_DISPLAYS);
+  session = vnc_find_session(pinfo->display);
+
+  /* Verify that the session is still valid */
+
+  if (session != NULL && session->state == VNCSERVER_RUNNING)
+    {
+      /* Queue the rectangular update */
+
+      ret = vnc_update_rectangle(session, rect);
+      if (ret < 0)
+        {
+          gdbg("ERROR: vnc_update_rectangle failed: %d\n", ret);
+        }
+    }
+}
+#endif

graphics/vnc/server/vnc_server.h

@@ -56,6 +56,14 @@
 
 /* Configuration */
 
+#ifndef CONFIG_NET_TCP_READAHEAD
+#  error CONFIG_NET_TCP_READAHEAD must be set to use VNC
+#endif
+
+#ifndef CONFIG_NX_UPDATE
+#  error CONFIG_NX_UPDATE must be set to use VNC
+#endif
+
 #if !defined(CONFIG_VNCSERVER_PROTO3p3) && !defined(CONFIG_VNCSERVER_PROTO3p8)
 #  error No VNC protocol selected
 #endif
@@ -268,6 +276,25 @@ int vnc_start_updater(FAR struct vnc_session_s *session);
 
 int vnc_stop_updater(FAR struct vnc_session_s *session);
 
+/****************************************************************************
+ * Name: vnc_update_rectangle
+ *
+ * Description:
+ *  Queue an update of the specified rectangular region on the display.
+ *
+ * Input Parameters:
+ *   session - An instance of the session structure.
+ *   rect    - The rectanglular region to be updated.
+ *
+ * Returned Value:
+ *   Zero (OK) is returned on success; a negated errno value is returned on
+ *   any failure.
+ *
+ ****************************************************************************/
+
+int vnc_update_rectangle(FAR struct vnc_session_s *session,
+                         FAR const struct nxgl_rect_s *rect);
+
 /****************************************************************************
  * Name: vnc_receiver
  *

graphics/vnc/server/vnc_updater.c

@@ -42,6 +42,7 @@
 #include <sched.h>
 #include <pthread.h>
 #include <assert.h>
+#include <errno.h>
 
 #include "vnc_server.h"
 
@@ -169,3 +170,31 @@ int vnc_stop_updater(FAR struct vnc_session_s *session)
   return OK;
 }
 
+/****************************************************************************
+ * Name: vnc_update_rectangle
+ *
+ * Description:
+ *  Queue an update of the specified rectangular region on the display.
+ *
+ * Input Parameters:
+ *   session - An instance of the session structure.
+ *   rect    - The rectanglular region to be updated.
+ *
+ * Returned Value:
+ *   Zero (OK) is returned on success; a negated errno value is returned on
+ *   any failure.
+ *
+ ****************************************************************************/
+
+int vnc_update_rectangle(FAR struct vnc_session_s *session,
+                         FAR const struct nxgl_rect_s *rect)
+{
+   /* Make sure that the rectangle has a area */
+
+   if (!nxgl_nullrect(rect))
+     {
+#warning Missing logic
+     }
+
+  return -ENOSYS;
+}