added VSYNC warning to console info overlay in developer mode

src/emucore/Console.hxx

@@ -367,6 +367,11 @@ class Console : public Serializable, public ConsoleIO
     */
     void changeJitterRecovery(int direction = +1) const;
 
+    /**
+      Return whether vertical sync length is according to spec.
+    */
+    bool vsyncCorrect() const { return myFrameManager->vsyncCorrect(); }
+
     /**
      * Update vcenter
      */

src/emucore/FBSurface.cxx

@@ -374,11 +374,11 @@ int FBSurface::drawString(const GUI::Font& font, const string& s,
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-void FBSurface::drawString(const GUI::Font& font, const string& s,
+int FBSurface::drawString(const GUI::Font& font, const string& s,
-                           int x, int y, int w,
+                          int x, int y, int w,
-                           ColorId color, TextAlign align,
+                          ColorId color, TextAlign align,
-                           int deltax, bool useEllipsis, ColorId shadowColor,
+                          int deltax, bool useEllipsis, ColorId shadowColor,
-                           size_t linkStart, size_t linkLen, bool underline)
+                          size_t linkStart, size_t linkLen, bool underline)
 {
 #ifdef GUI_SUPPORT
   const string ELLIPSIS = "\x1d"; // "..."
@@ -443,6 +443,7 @@ void FBSurface::drawString(const GUI::Font& font, const string& s,
     hLine(x0, y + font.getFontHeight() - 1, x1, kTextColorLink);
 
 #endif
+  return x;
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/FBSurface.hxx

@@ -251,12 +251,14 @@ class FBSurface
       @param linkLen      The length of a link in drawn string
       @param underline    Whether to underline the link
 
+      @return    x coordinate of end of string
+
     */
-    virtual void drawString(const GUI::Font& font, const string& s, int x, int y, int w,
+    virtual int drawString(const GUI::Font& font, const string& s, int x, int y, int w,
-                            ColorId color, TextAlign align = TextAlign::Left,
+                           ColorId color, TextAlign align = TextAlign::Left,
-                            int deltax = 0, bool useEllipsis = true, ColorId shadowColor = kNone,
+                           int deltax = 0, bool useEllipsis = true, ColorId shadowColor = kNone,
-                            size_t linkStart = string::npos, size_t linkLen = string::npos,
+                           size_t linkStart = string::npos, size_t linkLen = string::npos,
-                            bool underline = false);
+                           bool underline = false);
 
     /**
       Splits a given string to a given width considering whitespaces.

src/emucore/FrameBuffer.cxx

@@ -701,7 +701,7 @@ void FrameBuffer::drawFrameStats(float framesPerSecond)
   myStatsMsg.surface->invalidate();
 
   // draw scanlines
-  const ColorId color = myOSystem.console().tia().frameBufferScanlinesLastFrame() !=
+  ColorId color = myOSystem.console().tia().frameBufferScanlinesLastFrame() !=
     myLastScanlines ? kDbgColorRed : myStatsMsg.color;
 
   ss
@@ -734,10 +734,26 @@ void FrameBuffer::drawFrameStats(float framesPerSecond)
   ss.str("");
 
   ss << info.BankSwitch;
-  if (myOSystem.settings().getBool("dev.settings")) ss << "| Developer";
+  int xPosEnd =
+    myStatsMsg.surface->drawString(f, ss.str(), xPos, yPos,
+                                   myStatsMsg.w, myStatsMsg.color, TextAlign::Left, 0, true, kBGColor);
 
-  myStatsMsg.surface->drawString(f, ss.str(), xPos, yPos,
+  if(myOSystem.settings().getBool("dev.settings"))
-      myStatsMsg.w, myStatsMsg.color, TextAlign::Left, 0, true, kBGColor);
+  {
+    xPosEnd = myStatsMsg.surface->drawString(f, "| ", xPosEnd, yPos,
+                                  myStatsMsg.w, color, TextAlign::Left, 0, true, kBGColor);
+    ss.str("");
+    color = myStatsMsg.color;
+    if(myOSystem.console().vsyncCorrect())
+      ss << "Developer";
+    else
+    {
+      color = kDbgColorRed;
+      ss << "VSYNC!";
+    }
+    myStatsMsg.surface->drawString(f, ss.str(), xPosEnd, yPos,
+        myStatsMsg.w, color, TextAlign::Left, 0, true, kBGColor);
+  }
 
   myStatsMsg.surface->setDstPos(imageRect().x() + 10, imageRect().y() + 8);
   myStatsMsg.surface->setDstSize(myStatsMsg.w * hidpiScaleFactor(),

src/emucore/tia/frame-manager/AbstractFrameManager.hxx

@@ -148,6 +148,11 @@ class AbstractFrameManager : public Serializable
      */
     virtual void enableJitter(bool enabled) {}
 
+    /**
+     * Is vsync according to spec?
+     */
+    virtual bool vsyncCorrect() const { return true; }
+
     /**
      * The scanline difference between the last two frames. Used in the TIA to
      * clear any scanlines that were not repainted.

src/emucore/tia/frame-manager/FrameManager.hxx

@@ -55,6 +55,8 @@ class FrameManager: public AbstractFrameManager {
 
     void enableJitter(bool enabled) override { myJitterEnabled = enabled; }
 
+    bool vsyncCorrect() const override { return !myJitterEnabled || myJitterEmulation.vsyncCorrect(); }
+
     uInt32 height() const override { return myHeight; }
 
     uInt32 getY() const override { return myY; }

src/emucore/tia/frame-manager/JitterEmulation.cxx

@@ -76,6 +76,8 @@ void JitterEmulation::frameComplete(Int32 scanlineCount, Int32 vsyncCycles)
   const bool vsyncLinesStable = abs(vsyncCycles - myLastFrameVsyncCycles) < myVsyncDelta1;
 #endif
 
+  myVsyncCorrect = abs(vsyncCycles - 76 * 3) <= 3; // 3 cycles tolerance
+
   if(!scanlinesStable || !vsyncCyclesStable || !vsyncLinesStable)
   {
     if(++myUnstableCount >= myUnstableFrames)

src/emucore/tia/frame-manager/JitterEmulation.hxx

@@ -50,6 +50,8 @@ class JitterEmulation : public Serializable
     void frameComplete(Int32 scanlineCount, Int32 vsyncCycles);
     Int32 jitter() const { return myJitter; }
 
+    bool vsyncCorrect() const { return myVsyncCorrect; }
+
     /**
      * Save state.
      */
@@ -101,6 +103,7 @@ class JitterEmulation : public Serializable
     Int32 myUnstableFrames{MAX_UNSTABLE_FRAMES};
     Int32 myJitterLines{MIN_JITTER_LINES};
     Int32 myVsyncLines{MIN_VSYNC_LINES};
+    bool myVsyncCorrect{true};
 
   private:
     JitterEmulation(const JitterEmulation&) = delete;