diff -r cd6d76b9b47e -r 434d6b8a406d MiniDisplay/FutabaVfd.cpp
--- a/MiniDisplay/FutabaVfd.cpp	Fri May 30 10:56:20 2014 +0200
+++ b/MiniDisplay/FutabaVfd.cpp	Fri May 30 13:45:14 2014 +0200
@@ -4,6 +4,11 @@
 #include <string.h>
 
 
+#ifdef DEBUG_FRAME_DIFF
+#include <QImage>
+#include <QTextStream>
+#endif
+
 //
 //
 //
@@ -378,7 +383,7 @@
         if (iNeedFullFrameUpdate<3)
             {
             //TODO: enable this once SendModifiedPixelBlocks works
-            //iNeedFullFrameUpdate++;
+            iNeedFullFrameUpdate++;
             SetPixelBlock(0,0,63,FrameBufferSizeInBytes(),iFrameNext->Ptr());
             }
         else
@@ -387,14 +392,18 @@
             }
 		//Swap device front and back buffer
 		SetDisplayPosition(iDisplayPositionX,OffScreenY());
-		//Swap host buffers
-        //BitArray* nextFrame=iFrameNext;
-        //iFrameCurrent = iFramePrevious;
-        //iFrameNext = iFramePrevious;
 
+        //Cycle through our frame buffers
+        //We keep track of previous frame which is in fact our device back buffer.
+        //We can then compare previous and next frame and send only the differences to our device.
+        //This mechanism allows us to reduce traffic over our USB bus thus improving our frame rate from 14 FPS to 30 FPS.
+        //Keep our previous frame pointer
         BitArray* previousFrame=iFramePrevious;
+        //Current frame becomes the previous one
         iFramePrevious = iFrameCurrent;
+        //Next frame becomes the current one
         iFrameCurrent = iFrameNext;
+        //Next frame is now our former previous
         iFrameNext = previousFrame;
 		}
 	}
@@ -414,10 +423,10 @@
     int w=WidthInPixels();
     int h=HeightInPixels();
 
-    BitArray block(16*16);
 
 
     //TODO: optimize with memcmp and 16 inc
+    /*
     for (int i=0;i<w;i++)
         {
         for (int j=0;j<h;j++)
@@ -434,34 +443,61 @@
                 }
             }
         }
+    */
 
-    /*
+    BitArray nextBlock(16*16);
+    BitArray previousBlock(16*16);
+
     for (int i=0;i<w;i+=16)
         {
         for (int j=0;j<h;j+=16)
             {
             //aX*HeightInPixels()+aY
-            int offset=(i*w/8)+(j/8);
-            if (memcmp(iNextFrame->Ptr()+offset,iCurrentFrame->Ptr()+offset,32 )) //32=(16*16/8)
+            //int offset=(i*w/8)+(j/8);
+
+#ifdef DEBUG_FRAME_DIFF
+            QImage imagePrevious(16,16,QImage::Format_RGB32);
+            QImage imageNext(16,16,QImage::Format_RGB32);
+#endif
+
+            //Get both our blocks from our buffers
+            for (int x=i;x<i+16;x++)
+                {
+                for (int y=j;y<j+16;y++)
+                    {
+                    nextBlock.SetBitValue((x-i)*16+(y-j),(*iFrameNext)[x*h+y]);
+                    previousBlock.SetBitValue((x-i)*16+(y-j),(*iFramePrevious)[x*h+y]);
+
+#ifdef DEBUG_FRAME_DIFF
+                    imageNext.setPixel(x-i,y-j,(nextBlock[(x-i)*16+(y-j)]?0xFFFFFFFF:0x00000000));
+                    imagePrevious.setPixel(x-i,y-j,(previousBlock[(x-i)*16+(y-j)]?0xFFFFFFFF:0x00000000));
+#endif
+                    }
+                }
+
+#ifdef DEBUG_FRAME_DIFF
+            QString previousName;
+            QString nextName;
+            QTextStream(&previousName) << "p" << i << "x" << j << ".png";
+            QTextStream(&nextName) << "n" << i << "x" << j << ".png";
+            imagePrevious.save(previousName);
+            imageNext.save(nextName);
+#endif
+
+
+            //if (memcmp(iFrameNext->Ptr()+offset,iFramePrevious->Ptr()+offset,32 )) //32=(16*16/8)
+            if (memcmp(nextBlock.Ptr(),previousBlock.Ptr(),32 )!=0) //32=(16*16/8)
                 {
                 //We need to update that block
-
-                for (int x=i;x<i+16;x++)
-                    {
-                    for (int y=i;y<j+16;y++)
-                        {
-                        block.SetBitValue((x-i)*h+(y-j),(*iNextFrame)[x*h+y]);
-                        }
-                    }
-                SetPixelBlock(i,j,15,32,block.Ptr());
+                SetPixelBlock(i,j,15,32,nextBlock.Ptr());
+                //SetPixelBlock(i,j,15,32,0xFF/*nextBlock.Ptr()*/);
                 //SetDisplayPosition(iDisplayPositionX,OffScreenY());
                 //SetDisplayPosition(iDisplayPositionX,OffScreenY());
 
-                //SetPixelBlock(i,j,15,32,iNextFrame->Ptr()+offset);
+                //SetPixelBlock(i,j,15,32,iFrameNext->Ptr()+offset);
                 }
             }
         }
-    */
 
     }