Qt: OpenIGTLink: smooth out image times between successive frames

A small adjustment for less jumpy FPS numbers.

Author: ClaudioHoffmann

examples/solum_qt/solum/openigtlink.cpp

@@ -10,6 +10,7 @@ SolumIGTL::SolumIGTL()
         {
             emit clientConnected(true);
             clientConnectTimer_.stop();
+            msSinceLastFrame_ = 0;
             fpsSignalTimer_.start(1000);
         }
     });
@@ -79,7 +80,12 @@ void SolumIGTL::sendImage(const void* img, int w, int h, int bpp, size_t sz)
     if (!imageTimer_.isValid())
         imageTimer_.start();
     else
-        msSinceLastFrame_ = imageTimer_.restart();
+    {
+        constexpr double SMOOTHING = 0.75;
+        static_assert(SMOOTHING < 1.0);
+        msSinceLastFrame_ = ((msSinceLastFrame_ * SMOOTHING) +
+                             (imageTimer_.restart() * (1.0 - SMOOTHING)));
+    }
 }
 
 void SolumIGTL::disconnectClient()

examples/solum_qt/solum/openigtlink.h

@@ -22,7 +22,7 @@ class SolumIGTL : public QObject
 
 signals:
     void clientConnected(bool);
-    void msSinceLastFrame(qint64);
+    void msSinceLastFrame(double);
 
 private:
     void disconnectClient();
@@ -42,5 +42,5 @@ class SolumIGTL : public QObject
     // FPS timer
     QElapsedTimer imageTimer_;
 
-    qint64 msSinceLastFrame_;
+    double msSinceLastFrame_;
 };