Try to optimize

src/engine/audio.rs

@@ -85,6 +85,7 @@ struct SpectrumAnalyzer {
     fft: Arc<dyn rustfft::Fft<f32>>,
     window: [f32; FFT_SIZE],
     scratch: Vec<Complex<f32>>,
+    fft_buf: Vec<Complex<f32>>,
     band_edges: [usize; NUM_BANDS + 1],
 }
 
@@ -114,6 +115,7 @@ impl SpectrumAnalyzer {
             fft,
             window,
             scratch: vec![Complex::default(); scratch_len],
+            fft_buf: vec![Complex::default(); FFT_SIZE],
             band_edges,
         }
     }
@@ -130,20 +132,19 @@ impl SpectrumAnalyzer {
     }
 
     fn run_fft(&mut self, output: &SpectrumBuffer) {
-        let mut buf: Vec<Complex<f32>> = (0..FFT_SIZE)
-            .map(|i| {
-                let idx = (self.pos + i) % FFT_SIZE;
-                Complex::new(self.ring[idx] * self.window[i], 0.0)
-            })
-            .collect();
+        for i in 0..FFT_SIZE {
+            let idx = (self.pos + i) % FFT_SIZE;
+            self.fft_buf[i] = Complex::new(self.ring[idx] * self.window[i], 0.0);
+        }
 
-        self.fft.process_with_scratch(&mut buf, &mut self.scratch);
+        self.fft
+            .process_with_scratch(&mut self.fft_buf, &mut self.scratch);
 
         let mut bands = [0.0f32; NUM_BANDS];
         for (band, mag) in bands.iter_mut().enumerate() {
             let lo = self.band_edges[band];
             let hi = self.band_edges[band + 1].max(lo + 1);
-            let sum: f32 = buf[lo..hi].iter().map(|c| c.norm()).sum();
+            let sum: f32 = self.fft_buf[lo..hi].iter().map(|c| c.norm()).sum();
             let avg = sum / (hi - lo) as f32;
             let amplitude = avg / (FFT_SIZE as f32 / 2.0);
             let db = 20.0 * amplitude.max(1e-10).log10();