COMMENTS,POLISHING: comments fenzy around VisualProcessor machinery,

make process() a true interface as strong hint for derived classes,
plus misc define added for understanding.

BUGFIX: FFTDataDistributor loses incoming samples when compacting internal buffers.

BUGFIX2: FFTDistributor: Frozen Waterfall if internal buffer is no bigger than fftSize

src/panel/WaterfallPanel.cpp

@@ -39,6 +39,7 @@ void WaterfallPanel::refreshTheme() {
 void WaterfallPanel::setPoints(std::vector<float> &points) {
     size_t halfPts = points.size()/2;
     if (halfPts == fft_size) {
+       
         for (unsigned int i = 0; i < fft_size; i++) {
             this->points[i] = points[i*2+1];
         }
@@ -102,6 +103,10 @@ void WaterfallPanel::update() {
         
         unsigned char *waterfall_tex;
         
+        //Creates 2x 2D textures into card memory.
+        //of size half_fft_size * waterfall_lines, which can be BIG.
+        //The limit of the size of Waterfall is the size of the maximum supported 2D texture 
+        //by the graphic card. (half_fft_size * waterfall_lines, i.e DEFAULT_DEMOD_WATERFALL_LINES_NB * DEFAULT_FFT_SIZE/2)
         waterfall_tex = new unsigned char[half_fft_size * waterfall_lines];
         memset(waterfall_tex, 0, half_fft_size * waterfall_lines);