Use log scale for visualizer (#397)

* Visualizer: use log scale

- log scale frequency and gain
- Hamming windowing
- improve reading from fifo

* Fix Visualizer memory leaks

* Visualizer: use Blackman window

* Visualizer: support DFT zero padding

* Visualizer: support fractional height bars, fix fifo read

* Revert "Fix Visualizer memory leaks"

This reverts commit 5c6509d2b8ed985a4928f681217dc8616d053ace.

* Visualizer: fix fifo read again

* Visualizer: add cubic interpolation option

* Visualizer: Expose more config options, add docs for config options

* Visualizer: Use reverse video text for stereo visualizer smooth look

* Visualizer: use FormattedColor to for reverse-video

* Visualizer: change some config options for spectrum

* Fix build fftw disabled

* Visualizer: use [0,5] interval for dft_size config option

src/settings.cpp

@@ -291,6 +291,26 @@ bool Configuration::read(const std::vector<std::string> &config_paths, bool igno
 			boundsCheck<std::wstring::size_type>(result.size(), 2, 2);
 			return result;
 	});
+	p.add("visualizer_autoscale", &visualizer_autoscale, "yes", yes_no);
+	p.add("visualizer_spectrum_smooth_look", &visualizer_spectrum_smooth_look, "yes", yes_no);
+	p.add("visualizer_spectrum_dft_size", &visualizer_spectrum_dft_size,
+			"12", [](std::string v) {
+      uint32_t result = verbose_lexical_cast<uint32_t>(v);
+      boundsCheck<uint32_t>(result, 0, 5);
+			return result + 12;
+			});
+	p.add("visualizer_spectrum_hz_min", &visualizer_spectrum_hz_min,
+			"20", [](std::string v) {
+			auto result = verbose_lexical_cast<double>(v);
+			lowerBoundCheck<double>(result, 1);
+			return result;
+			});
+	p.add("visualizer_spectrum_hz_max", &visualizer_spectrum_hz_max,
+			"20000", [](std::string v) {
+			auto result = verbose_lexical_cast<double>(v);
+			lowerBoundCheck<double>(result, Config.visualizer_spectrum_hz_min+1);
+			return result;
+			});
 	p.add("visualizer_color", &visualizer_colors,
 	      "blue, cyan, green, yellow, magenta, red", list_of<NC::FormattedColor>);
 	p.add("system_encoding", &system_encoding, "", [](std::string encoding) {