documentation on the interface

components/rgbd-sources/include/ftl/rgbd/frame.hpp

@@ -71,9 +71,14 @@ public:
 	 * @param	Channel type
 	 * @returns	Reference to channel data
 	 * 
-	 * Returns non-const reference to channel data. Invalidates other copies of
-	 * the data (host/gpu) for the specified channel, next time getChannel() is
-	 * called a memory transfer may occur.
+	 * Returns non-const reference to channel memory. Invalidates other copies
+	 * of the data (host/gpu) for the specified channel, next time getChannel()
+	 * is called a memory transfer may occur.
+	 * 
+	 * NOTE:	If user of setChannel<T>() wants to modify contents instead of
+	 * 			replacing them, getChannel<T>() needs to be called first to
+	 * 			ensure there is valid contents in the returned reference!
+	 * 			(TODO: interface could be improved)
 	 */
 	template <typename T> T& setChannel(const ftl::rgbd::channel_t& channel);
 

components/rgbd-sources/src/algorithms/fixstars_sgm.cpp

@@ -118,6 +118,7 @@ void FixstarsSGM::compute(ftl::rgbd::Frame &frame, cv::cuda::Stream &stream)
 #ifdef HAVE_OPTFLOW
 	if (use_off_)
 	{
+		frame.getChannel<Mat>(ftl::rgbd::kChanDisparity);
 		off_.filter(frame.setChannel<Mat>(ftl::rgbd::kChanDisparity), Mat(lbw_));
 	}
 #endif