add basic spectrum function

packages/draw/draw.mjs

@@ -26,7 +26,7 @@ export const getDrawContext = (id = 'test-canvas', options) => {
       }, 200);
     });
   }
-  return canvas.getContext(contextType);
+  return canvas.getContext(contextType, { willReadFrequently: true });
 };
 
 let animationFrames = {};

packages/superdough/superdough.mjs

@@ -270,11 +270,12 @@ function getReverb(orbit, duration, fade, lp, dim, ir) {
 export let analysers = {},
   analysersData = {};
 
-export function getAnalyserById(id, fftSize = 1024) {
+export function getAnalyserById(id, fftSize = 1024, smoothingTimeConstant = 0.5) {
   if (!analysers[id]) {
     // make sure this doesn't happen too often as it piles up garbage
     const analyserNode = getAudioContext().createAnalyser();
     analyserNode.fftSize = fftSize;
+    analyserNode.smoothingTimeConstant = smoothingTimeConstant;
     // getDestination().connect(analyserNode);
     analysers[id] = analyserNode;
     analysersData[id] = new Float32Array(analysers[id].frequencyBinCount);

packages/webaudio/index.mjs

@@ -6,4 +6,5 @@ This program is free software: you can redistribute it and/or modify it under th
 
 export * from './webaudio.mjs';
 export * from './scope.mjs';
+export * from './spectrum.mjs';
 export * from 'superdough';

packages/webaudio/spectrum.mjs

@@ -0,0 +1,57 @@
+import { Pattern, clamp } from '@strudel/core';
+import { getDrawContext, getTheme } from '@strudel/draw';
+import { analysers, getAnalyzerData } from 'superdough';
+
+/**
+ * Renders a spectrum analyzer for the incoming audio signal.
+ * @name spectrum
+ * @param {object} config optional config with options:
+ */
+let latestColor = {};
+Pattern.prototype.spectrum = function (config = {}) {
+  let id = config.id ?? 1;
+  return this.analyze(id).draw(
+    (haps) => {
+      config.color = haps[0]?.value?.color || latestColor[id] || getTheme().foreground;
+      latestColor[id] = config.color;
+      drawSpectrum(analysers[id], config);
+    },
+    { id },
+  );
+};
+
+Pattern.prototype.scope = Pattern.prototype.tscope;
+
+const lastFrames = new Map();
+
+function drawSpectrum(
+  analyser,
+  { thickness = 3, speed = 1, min = -80, max = 0, ctx = getDrawContext(), id = 1, color } = {},
+) {
+  ctx.lineWidth = thickness;
+  ctx.strokeStyle = color;
+
+  if (!analyser) {
+    // if analyser is undefined, draw straight line
+    // it may be undefined when no sound has been played yet
+    return;
+  }
+  const scrollSize = speed;
+  const dataArray = getAnalyzerData('frequency', id);
+  const canvas = ctx.canvas;
+  ctx.fillStyle = color;
+  const bufferSize = analyser.frequencyBinCount;
+  let imageData = lastFrames.get(id) || ctx.getImageData(0, 0, canvas.width, canvas.height);
+  lastFrames.set(id, imageData);
+  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+  ctx.putImageData(imageData, -scrollSize, 0);
+  let q = canvas.width - speed;
+  for (let i = 0; i < bufferSize; i++) {
+    const normalized = clamp((dataArray[i] - min) / (max - min), 0, 1);
+    ctx.globalAlpha = normalized;
+    const next = (Math.log(i + 1) / Math.log(bufferSize)) * canvas.height;
+    const size = 2; //next - pos;
+    ctx.fillRect(q, canvas.height - next, scrollSize, size);
+  }
+  lastFrames.set(id, ctx.getImageData(0, 0, canvas.width, canvas.height));
+}