Add support for X Present extension

This makes it possible for applications to synchronize their updates to
the updates sent out to clients. This avoids tearing, and could in the
future also help with rate limiting applications to what the client can
actually show.

common/rfb/SDesktop.h

@@ -87,6 +87,10 @@ namespace rfb {
       return resultProhibited;
     }
 
+    // frameTick() is called whenever a frame update has been processed,
+    // signalling that a good time to render new data
+    virtual void frameTick(uint64_t msc) { (void)msc; }
+
     // InputHandler interface
     // pointerEvent(), keyEvent() and clientCutText() are called in response to
     // the relevant RFB protocol messages from clients.

common/rfb/VNCServer.h

@@ -42,6 +42,8 @@ namespace rfb {
     virtual void blockUpdates() = 0;
     virtual void unblockUpdates() = 0;
 
+    virtual uint64_t getMsc() = 0;
+
     // setPixelBuffer() tells the server to use the given pixel buffer (and
     // optionally a modified screen layout).  If this differs in size from
     // the previous pixel buffer, this may result in protocol messages being

common/rfb/VNCServerST.cxx

@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2009-2019 Pierre Ossman for Cendio AB
+ * Copyright 2009-2024 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -88,7 +88,7 @@ VNCServerST::VNCServerST(const char* name_, SDesktop* desktop_)
     renderedCursorInvalid(false),
     keyRemapper(&KeyRemapper::defInstance),
     idleTimer(this), disconnectTimer(this), connectTimer(this),
-    frameTimer(this)
+    msc(0), frameTimer(this)
 {
   slog.debug("creating single-threaded server %s", name.c_str());
 
@@ -257,6 +257,11 @@ void VNCServerST::unblockUpdates()
   }
 }
 
+uint64_t VNCServerST::getMsc()
+{
+  return msc;
+}
+
 void VNCServerST::setPixelBuffer(PixelBuffer* pb_, const ScreenSet& layout)
 {
   if (comparer)
@@ -634,6 +639,9 @@ void VNCServerST::handleTimeout(Timer* t)
 
     writeUpdate();
 
+    msc++;
+    desktop->frameTick(msc);
+
     // If this is the first iteration then we need to adjust the timeout
     frameTimer.repeat(1000/rfb::Server::frameRate);
   } else if (t == &idleTimer) {

common/rfb/VNCServerST.h

@@ -81,6 +81,7 @@ namespace rfb {
 
     virtual void blockUpdates();
     virtual void unblockUpdates();
+    virtual uint64_t getMsc();
     virtual void setPixelBuffer(PixelBuffer* pb, const ScreenSet& layout);
     virtual void setPixelBuffer(PixelBuffer* pb);
     virtual void setScreenLayout(const ScreenSet& layout);
@@ -206,6 +207,7 @@ namespace rfb {
     Timer disconnectTimer;
     Timer connectTimer;
 
+    uint64_t msc;
     Timer frameTimer;
   };
 

unix/xserver/hw/vnc/Makefile.am

@@ -11,12 +11,12 @@ COMMON_LIBS=$(NETWORK_LIB) $(RFB_LIB) $(RDR_LIB) $(OS_LIB) $(UNIXCOMMON_LIB)
 noinst_LTLIBRARIES = libvnccommon.la
 
 HDRS = vncExtInit.h vncHooks.h \
-	vncBlockHandler.h vncSelection.h \
+	vncBlockHandler.h vncPresent.h vncSelection.h \
 	XorgGlue.h XserverDesktop.h xorg-version.h \
 	vncInput.h RFBGlue.h
 
 libvnccommon_la_SOURCES = $(HDRS) \
-	vncExt.c vncExtInit.cc vncHooks.c vncSelection.c \
+	vncExt.c vncExtInit.cc vncHooks.c vncPresent.c vncSelection.c \
 	vncBlockHandler.c XorgGlue.c RandrGlue.c RFBGlue.cc XserverDesktop.cc \
 	vncInput.c vncInputXKB.c qnum_to_xorgevdev.c qnum_to_xorgkbd.c
 

unix/xserver/hw/vnc/XserverDesktop.cc

@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2009-2019 Pierre Ossman for Cendio AB
+ * Copyright 2009-2024 Pierre Ossman for Cendio AB
  * Copyright 2014 Brian P. Hinz
  * 
  * This is free software; you can redistribute it and/or modify
@@ -54,6 +54,7 @@
 
 extern "C" {
 void vncSetGlueContext(int screenIndex);
+void vncPresentMscEvent(uint64_t id, uint64_t msc);
 }
 
 using namespace rfb;
@@ -145,6 +146,21 @@ void XserverDesktop::refreshScreenLayout()
   server->setScreenLayout(::computeScreenLayout(&outputIdMap));
 }
 
+uint64_t XserverDesktop::getMsc()
+{
+  return server->getMsc();
+}
+
+void XserverDesktop::queueMsc(uint64_t id, uint64_t msc)
+{
+  pendingMsc[id] = msc;
+}
+
+void XserverDesktop::abortMsc(uint64_t id)
+{
+  pendingMsc.erase(id);
+}
+
 void XserverDesktop::init(rfb::VNCServer* vs)
 {
   // We already own the server object, and we always keep it in a
@@ -471,6 +487,22 @@ unsigned int XserverDesktop::setScreenLayout(int fb_width, int fb_height,
   return result;
 }
 
+void XserverDesktop::frameTick(uint64_t msc)
+{
+  std::map<uint64_t, uint64_t>::iterator iter, next;
+
+  for (iter = pendingMsc.begin(); iter != pendingMsc.end();) {
+    next = iter; next++;
+
+    if (iter->second <= msc) {
+      pendingMsc.erase(iter->first);
+      vncPresentMscEvent(iter->first, msc);
+    }
+
+    iter = next;
+  }
+}
+
 void XserverDesktop::handleClipboardRequest()
 {
   vncHandleClipboardRequest();

unix/xserver/hw/vnc/XserverDesktop.h

@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2009-2019 Pierre Ossman for Cendio AB
+ * Copyright 2009-2024 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -59,6 +59,9 @@ class XserverDesktop : public rfb::SDesktop, public rfb::FullFramePixelBuffer,
   void unblockUpdates();
   void setFramebuffer(int w, int h, void* fbptr, int stride);
   void refreshScreenLayout();
+  uint64_t getMsc();
+  void queueMsc(uint64_t id, uint64_t msc);
+  void abortMsc(uint64_t id);
   void requestClipboard();
   void announceClipboard(bool available);
   void sendClipboardData(const char* data);
@@ -96,6 +99,7 @@ class XserverDesktop : public rfb::SDesktop, public rfb::FullFramePixelBuffer,
   virtual void keyEvent(uint32_t keysym, uint32_t keycode, bool down);
   virtual unsigned int setScreenLayout(int fb_width, int fb_height,
                                        const rfb::ScreenSet& layout);
+  virtual void frameTick(uint64_t msc);
   virtual void handleClipboardRequest();
   virtual void handleClipboardAnnounce(bool available);
   virtual void handleClipboardData(const char* data);
@@ -128,6 +132,8 @@ class XserverDesktop : public rfb::SDesktop, public rfb::FullFramePixelBuffer,
 
   OutputIdMap outputIdMap;
 
+  std::map<uint64_t, uint64_t> pendingMsc;
+
   rfb::Point oldCursorPos;
 };
 #endif

unix/xserver/hw/vnc/vncExtInit.cc

@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2011-2019 Pierre Ossman for Cendio AB
+ * Copyright 2011-2024 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -482,6 +482,33 @@ void vncRefreshScreenLayout(int scrIdx)
   }
 }
 
+uint64_t vncGetMsc(int scrIdx)
+{
+  try {
+    return desktop[scrIdx]->getMsc();
+  } catch (rdr::Exception& e) {
+    vncFatalError("vncGetMsc: %s\n", e.str());
+  }
+}
+
+void vncQueueMsc(int scrIdx, uint64_t id, uint64_t msc)
+{
+  try {
+    desktop[scrIdx]->queueMsc(id, msc);
+  } catch (rdr::Exception& e) {
+    vncFatalError("vncQueueMsc: %s\n", e.str());
+  }
+}
+
+void vncAbortMsc(int scrIdx, uint64_t id)
+{
+  try {
+    desktop[scrIdx]->abortMsc(id);
+  } catch (rdr::Exception& e) {
+    vncFatalError("vncAbortMsc: %s\n", e.str());
+  }
+}
+
 int vncOverrideParam(const char *nameAndValue)
 {
   const char* equalSign = strchr(nameAndValue, '=');

unix/xserver/hw/vnc/vncExtInit.h

@@ -1,5 +1,5 @@
 /* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
- * Copyright 2011-2019 Pierre Ossman for Cendio AB
+ * Copyright 2011-2024 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -87,6 +87,10 @@ void vncPreScreenResize(int scrIdx);
 void vncPostScreenResize(int scrIdx, int success, int width, int height);
 void vncRefreshScreenLayout(int scrIdx);
 
+uint64_t vncGetMsc(int scrIdx);
+void vncQueueMsc(int scrIdx, uint64_t id, uint64_t msc);
+void vncAbortMsc(int scrIdx, uint64_t id);
+
 int vncOverrideParam(const char *nameAndValue);
 
 #ifdef __cplusplus

unix/xserver/hw/vnc/vncPresent.c

@@ -0,0 +1,93 @@
+/* Copyright 2024 Pierre Ossman for Cendio AB
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifdef HAVE_DIX_CONFIG_H
+#include <dix-config.h>
+#endif
+
+#include "vncExtInit.h"
+#include "vncPresent.h"
+
+#include <present.h>
+
+static RRCrtcPtr vncPresentGetCrtc(WindowPtr window)
+{
+  ScreenPtr pScreen = window->drawable.pScreen;
+  rrScrPrivPtr rp = rrGetScrPriv(pScreen);
+
+  /* All output is synchronized, so just pick the first active crtc */
+  for (int c = 0; c < rp->numCrtcs; c++) {
+    RRCrtcPtr crtc;
+
+    crtc = rp->crtcs[c];
+    if (crtc->mode == NULL)
+      continue;
+
+    return crtc;
+  }
+
+  return NULL;
+}
+
+static int vncPresentGetUstMsc(RRCrtcPtr crtc, CARD64 *ust, CARD64 *msc)
+{
+  *ust = GetTimeInMicros();
+  *msc = vncGetMsc(crtc->pScreen->myNum);
+
+  return Success;
+}
+
+static int vncPresentQueueVBlank(RRCrtcPtr crtc, uint64_t event_id,
+                                 uint64_t msc)
+{
+  vncQueueMsc(crtc->pScreen->myNum, event_id, msc);
+  return Success;
+}
+
+void vncPresentMscEvent(uint64_t id, uint64_t msc)
+{
+  present_event_notify(id, GetTimeInMicros(), msc);
+}
+
+static void vncPresentAbortVBlank(RRCrtcPtr crtc, uint64_t event_id,
+                                  uint64_t msc)
+{
+  vncAbortMsc(crtc->pScreen->myNum, event_id);
+}
+
+static void vncPresentFlush(WindowPtr window)
+{
+}
+
+static present_screen_info_rec vncPresentScreenInfo = {
+  .version = PRESENT_SCREEN_INFO_VERSION,
+
+  .get_crtc = vncPresentGetCrtc,
+  .get_ust_msc = vncPresentGetUstMsc,
+  .queue_vblank = vncPresentQueueVBlank,
+  .abort_vblank = vncPresentAbortVBlank,
+  .flush = vncPresentFlush,
+
+  .capabilities = PresentCapabilityNone,
+};
+
+Bool
+vncPresentInit(ScreenPtr screen)
+{
+  return present_screen_init(screen, &vncPresentScreenInfo);
+}

unix/xserver/hw/vnc/vncPresent.h

@@ -0,0 +1,27 @@
+/* Copyright 2024 Pierre Ossman for Cendio AB
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifndef __PRESENT_H__
+#define __PRESENT_H__
+
+#include <dix.h>
+
+Bool vncPresentInit(ScreenPtr screen);
+void vncPresentMscEvent(uint64_t id, uint64_t msc);
+
+#endif

unix/xserver/hw/vnc/xvnc.c

@@ -36,6 +36,7 @@ from the X Consortium.
 #include "RFBGlue.h"
 #include "XorgGlue.h"
 #include "RandrGlue.h"
+#include "vncPresent.h"
 #include "xorg-version.h"
 
 #include <stdio.h>
@@ -1085,6 +1086,10 @@ vncScreenInit(ScreenPtr pScreen, int argc, char **argv)
     if (!ret)
         return FALSE;
 
+    ret = vncPresentInit(pScreen);
+    if (!ret)
+        ErrorF("Failed to initialize Present extension\n");
+
     return TRUE;
 
 }                               /* end vncScreenInit */