foo.diff

diff --git a/rust-wasm-bindgen/dist/index.html b/rust-wasm-bindgen/dist/index.html
index 4db5b19..bb5fe0f 100644
--- a/rust-wasm-bindgen/dist/index.html
+++ b/rust-wasm-bindgen/dist/index.html
@@ -14,11 +14,11 @@
 <script src="drift_meter.js"></script>
 <script src="colormap.js"></script>
 <script>
-    const {process_audio} = wasm_bindgen;
+    const { Context } = wasm_bindgen;
 
-    let drift_meter;
-    wasm_bindgen('./drift_meter_bg.wasm').then(function (d) {
-        drift_meter = d;
+    let cx = null;
+    wasm_bindgen('./drift_meter_bg.wasm').then(function () {
+        cx = Context.new();
     });
 
     function start() {
@@ -45,7 +45,11 @@
             let scriptNode = audioCtx.createScriptProcessor(2048, 1, 1);
             scriptNode.onaudioprocess = function (audioProcessingEvent) {
                 const inputBuffer = audioProcessingEvent.inputBuffer;
-                const chroma = process_audio(inputBuffer.getChannelData(0));
+                cx.process_audio(inputBuffer.getChannelData(0));
+                const ptr = cx.result_ptr();
+                const len = cx.result_len();
+                const chroma = new Float32Array(wasm_bindgen.wasm.memory.buffer)
+                  .subarray(ptr / 4, ptr / 4 + len);
                 const barHeight = HEIGHT / chroma.length;
 
                 canvasCtx.drawImage(canvasElement, -SPEED, 0);
diff --git a/rust-wasm-bindgen/src/lib.rs b/rust-wasm-bindgen/src/lib.rs
index 0342463..a2d89c1 100644
--- a/rust-wasm-bindgen/src/lib.rs
+++ b/rust-wasm-bindgen/src/lib.rs
@@ -12,12 +12,23 @@ use wasm_bindgen::prelude::*;
 mod filterbank;
 
 #[wasm_bindgen]
-pub fn process_audio(buf: Vec<f32>) -> Vec<f32> {
-    // Create FFT processor
-    let mut fft: RFft1D<f32> = RFft1D::<f32>::new(2048);
+pub struct Context {
+    fft: RFft1D<f32>,
+    result: [f32; 12],
+}
+
+#[wasm_bindgen]
+impl Context {
+    pub fn new() -> Context {
+        Context {
+            fft: RFft1D::new(2048),
+            result: [0.0; 12],
+        }
+    }
 
+    pub fn process_audio(&mut self, buf: &[f32]) {
         // Do FFT
-    let bins = fft.forward(&buf);
+        let bins = self.fft.forward(buf);
 
         // Square FFT coeffs
         let bins = bins.iter().map(|x| x.norm_sqr()).collect();
@@ -48,12 +59,18 @@ pub fn process_audio(buf: Vec<f32>) -> Vec<f32> {
 
         let p = 0.5 * (a - c) / (a - (2. * b) + c);
 
-    let mut hpcp: Vec<f32> = Vec::with_capacity(12);
         for i in 0..12 {
-        hpcp.push(reshaped_chroma[[i, b_index]] - (0.25 * (reshaped_chroma[[i, a_index]] - reshaped_chroma[[i, c_index]]) * p));
+            self.result[i] = reshaped_chroma[[i, b_index]] - (0.25 * (reshaped_chroma[[i, a_index]] - reshaped_chroma[[i, c_index]]) * p);
+        }
+    }
+
+    pub fn result_ptr(&self) -> *const f32 {
+        self.result.as_ptr()
     }
 
-    hpcp
+    pub fn result_len(&self) -> usize {
+        self.result.len()
+    }
 }