actually use pulseaudio (works around several ALSA bugs/problems)

README

@@ -0,0 +1,4 @@
+* set pulseaudio to 192kHz sample rate:
+  hardware.pulseaudio.daemon.config = { "default-sample-rate" = 192000; };
+* check that sound card is operating at 192kHz:
+  cat /proc/asound/card0/pcm0c/sub0/hw_params 

main.cpp

@@ -6,6 +6,7 @@
 #include <mutex>
 #include <vector>
 #include <complex>
+#include <chrono>
 
 #include <GLFW/glfw3.h>
 
@@ -27,7 +28,11 @@ static int waterfall_width = 1600;
 static int waterfall_height = 700;
 static unsigned int waterfall_data[1600*700];
 
+static std::atomic<int> fps;
+
 static void dsp_thread() {
+    using namespace std::literals::chrono_literals;
+
     size_t len = 6400;
     std::vector<short int> frames(len);
 
@@ -43,6 +48,8 @@ static void dsp_thread() {
     for(size_t i=0; i<shape.size(); ++i)
         axes.push_back(i);
     std::vector<std::complex<float>> frames_ft(len);
+    int iterations = 0;
+    auto last_second = std::chrono::steady_clock::now();
     while(!terminate_dsp) {
         int read_count = snd_pcm_readi(pcm, frames.data(), len);
         if(read_count < 0) {
@@ -59,18 +66,17 @@ static void dsp_thread() {
                 waterfall_data[i] = 0xff000000 | 0x010101*std::min(int(abs(frames_ft[i*len/(4*waterfall_width)])/10000.), 255);
             }
         }
+        iterations++;
+        if((std::chrono::steady_clock::now() - last_second) >= 1s) {
+            fps = iterations;
+            iterations = 0;
+            last_second += 1s;
+        }
     };
 }
 
 int main(int argc, char* argv[])
 {
-    if(argc != 2) {
-        std::cerr << "please specify ALSA device on the command line" << std::endl;
-        std::cerr << "use arecord -L to list, and select raw device without pulseaudio" << std::endl;
-        return 1;
-    }
-    char* alsa_device = argv[1];
-
     if (!glfwInit()) {
         std::cerr << "failed to initialize GLFW" << std::endl;
         return 1;
@@ -113,7 +119,7 @@ int main(int argc, char* argv[])
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 
     int err;
-    if ((err = snd_pcm_open(&pcm, alsa_device, SND_PCM_STREAM_CAPTURE, 0)) < 0) {
+    if ((err = snd_pcm_open(&pcm, "default", SND_PCM_STREAM_CAPTURE, 0)) < 0) {
         std::cerr << "cannot open ALSA device: " << snd_strerror(err) << std::endl;
         return 1;
     }
@@ -200,6 +206,7 @@ int main(int argc, char* argv[])
         ImGui::TableNextColumn();
         if(ImGui::Button("Exit"))
             exit = true;
+        ImGui::Text("FPS: %d", (int)fps);
         ImGui::TableNextColumn();
         ImGui::Image((void*)(intptr_t)waterfall, ImVec2(waterfall_width, waterfall_height));
         ImGui::EndTable();