comments and improvement to fps printing

src/camera/camera-demo.cpp

@@ -149,16 +149,17 @@ int main(int argc, char **argv) {
     uint64_t cnt = 1;
     int64 start = cv::getTickCount();
     double tickFreq = cv::getTickFrequency();
+    double lastFps = 0;
 
     while (true) {
         //Activate the OpenCL context for OpenGL
         GL_CONTEXT.bind();
-        //Initially get the framebuffer so we can write the video frame to it
+        //Initially aquire the framebuffer so we can write the video frame to it
         gl::acquire_frame_buffer(frameBuffer);
 
         //Activate the OpenCL context for VAAPI
         VA_CONTEXT.bind();
-        //Decode a frame using HW acceleration into a cv::UMat
+        //Decode a frame on the GPU using VAAPI
         cap >> videoFrame;
         if (videoFrame.empty()) {
             cerr << "End of stream. Exiting" << endl;
@@ -173,10 +174,11 @@ int main(int argc, char **argv) {
         cv::resize(videoFrameRGBA, frameBuffer, cv::Size(WIDTH, HEIGHT));
 
         GL_CONTEXT.bind();
-        //Transfer buffer ownership to OpenGL
+        //Release the frame buffer for use by OpenGL
         gl::release_frame_buffer(frameBuffer);
+        //Render using OpenGL
         render();
-        //Transfer buffer ownership to OpenCL
+        //Aquire the frame buffer for use by OpenCL
         gl::acquire_frame_buffer(frameBuffer);
 
         //Glow effect (OpenCL)
@@ -194,7 +196,7 @@ int main(int argc, char **argv) {
         if(x11::is_initialized()) {
             //Yet again activate the OpenCL context for OpenGL
             GL_CONTEXT.bind();
-            //Transfer buffer ownership back to OpenGL
+            //Release the frame buffer for use by OpenGL
             gl::release_frame_buffer(frameBuffer);
             //Blit the framebuffer we have been working on to the screen
             gl::blit_frame_buffer_to_screen();
@@ -203,13 +205,15 @@ int main(int argc, char **argv) {
             if(x11::window_closed())
                 break;
 
+            //Transfer the back buffer (which we have been using as frame buffer) to the native window
             gl::swapBuffers();
         }
 
         //Measure FPS
-        if (cnt % uint64(INPUT_FPS) == 0) {
+        if (cnt % uint64(ceil(lastFps == 0 ? INPUT_FPS : lastFps)) == 0) {
             int64 tick = cv::getTickCount();
-            cerr << "FPS : " << tickFreq / ((tick - start + 1) / cnt) << '\r';
+            lastFps = tickFreq / ((tick - start + 1) / cnt);
+            cerr << "FPS : " << lastFps << '\r';
             start = tick;
             cnt = 1;
         }