rejig the fft code so that the buffer is always fresh

src/platform_common/FFT.cpp

@@ -12,59 +12,62 @@ namespace FFT
   kiss_fftr_cfg fftcfg;
   mal_context context;
   mal_device captureDevice;
-  float lastFFT[ FFT_SIZE ];
   float sampleBuf[ FFT_SIZE * 2 ];
-  int sampleCursor = 0;
+
+  void OnLog( mal_context* pContext, mal_device* pDevice, const char* message )
+  {
+    printf( "[FFT] [mal:%p:%p]\n %s", pContext, pDevice, message );
+  }
 
   void OnReceiveFrames( mal_device* pDevice, mal_uint32 frameCount, const void* pSamples )
   {
+    frameCount = frameCount < FFT_SIZE * 2 ? frameCount : FFT_SIZE * 2;
+
+    // Just rotate the buffer; copy existing, append new
     const mal_int16 * samples = (const mal_int16 *)pSamples;
+    float * p = sampleBuf;
+    for ( int i = 0; i < FFT_SIZE * 2 - frameCount; i++ )
+    {
+      *( p++ ) = sampleBuf[ i + frameCount ];
+    }
     for ( int i = 0; i < frameCount; i++ )
     {
-      sampleBuf[ sampleCursor++ ] = ( samples[ 0 ] + samples[ 1 ] ) / 65535.0f; // int16 max * 2 -> -1..1
-      samples += 2;      
-      if ( sampleCursor == FFT_SIZE * 2 )
-      {
-        kiss_fft_cpx out[ FFT_SIZE + 1 ];
-        kiss_fftr( fftcfg, sampleBuf, out );
-
-        for ( int i = 0; i < FFT_SIZE; i++ )
-        {
-          static const float scaling = 1.0f / (float)FFT_SIZE;
-          lastFFT[ i ] = 2.0 * sqrtf( out[ i ].r*out[ i ].r + out[ i ].i*out[ i ].i ) * scaling;
-        }
-
-        sampleCursor = 0;
-      }
+      *( p++ ) = ( samples[ i * 2 ] + samples[ i * 2 + 1 ] ) / 65535.0f; // int16 max * 2 -> -1..1
     }
   }
 
   bool Open()
   {
-    memset( lastFFT, 0, sizeof( float ) * FFT_SIZE );
+    memset( sampleBuf, 0, sizeof( float ) * FFT_SIZE * 2 );
 
     fftcfg = kiss_fftr_alloc( FFT_SIZE * 2, false, NULL, NULL );
 
-    if ( mal_context_init( NULL, 0, NULL, &context ) != MAL_SUCCESS )
+    const mal_context_config context_config = mal_context_config_init( OnLog );
+    mal_result result = mal_context_init( NULL, 0, &context_config, &context );
+    if ( result != MAL_SUCCESS )
     {
-      printf( "[FFT] Failed to initialize context." );
+      printf( "[FFT] Failed to initialize context: %d", result );
       return false;
     }
 
-    mal_device_config config = mal_device_config_init( mal_format_s16, 2, 44100, OnReceiveFrames, NULL );
+    printf( "[FFT] MAL context initialized, backend is '%s'\n", mal_get_backend_name( context.backend ) );
+
+    const mal_device_config config = mal_device_config_init( mal_format_s16, 2, 44100, OnReceiveFrames, NULL );
     
-    if ( mal_device_init( &context, mal_device_type_capture, NULL, &config, NULL, &captureDevice ) != MAL_SUCCESS )
+    result = mal_device_init( &context, mal_device_type_capture, NULL, &config, NULL, &captureDevice );
+    if ( result != MAL_SUCCESS )
     {
       mal_context_uninit( &context );
-      printf( "[FFT] Failed to initialize capture device.\n" );
+      printf( "[FFT] Failed to initialize capture device: %d\n", result );
       return false;
     }
 
-    if ( mal_device_start( &captureDevice ) != MAL_SUCCESS )
+    result = mal_device_start( &captureDevice );
+    if ( result != MAL_SUCCESS )
     {
       mal_device_uninit( &captureDevice );
       mal_context_uninit( &context );
-      printf( "[FFT] Failed to start capture device.\n" );
+      printf( "[FFT] Failed to start capture device: %d\n", result );
       return false;
     }
 
@@ -72,7 +75,15 @@ namespace FFT
   }
   bool GetFFT( float * samples )
   {
-    memcpy( samples, lastFFT, sizeof( float )*FFT_SIZE );
+    kiss_fft_cpx out[ FFT_SIZE + 1 ];
+    kiss_fftr( fftcfg, sampleBuf, out );
+
+    for ( int i = 0; i < FFT_SIZE; i++ )
+    {
+      static const float scaling = 1.0f / (float)FFT_SIZE;
+      samples[ i ] = 2.0 * sqrtf( out[ i ].r * out[ i ].r + out[ i ].i * out[ i ].i ) * scaling;
+    }
+
     return true;
   }
   void Close()