Merge pull request #780 from tidalcycles/xfade

add xfade

packages/core/pattern.mjs

@@ -2392,3 +2392,29 @@ export const ref = (accessor) =>
   pure(1)
     .withValue(() => reify(accessor()))
     .innerJoin();
+
+let fadeGain = (p) => (p < 0.5 ? 1 : 1 - (p - 0.5) / 0.5);
+
+/**
+ * Cross-fades between left and right from 0 to 1:
+ * - 0 = (full left, no right)
+ * - .5 = (both equal)
+ * - 1 = (no left, full right)
+ *
+ * @name xfade
+ * @example
+ * xfade(s("bd*2"), "<0 .25 .5 .75 1>", s("hh*8"))
+ */
+export let xfade = (a, pos, b) => {
+  pos = reify(pos);
+  a = reify(a);
+  b = reify(b);
+  let gaina = pos.fmap((v) => ({ gain: fadeGain(v) }));
+  let gainb = pos.fmap((v) => ({ gain: fadeGain(1 - v) }));
+  return stack(a.mul(gaina), b.mul(gainb));
+};
+
+// the prototype version is actually flipped so left/right makes sense
+Pattern.prototype.xfade = function (pos, b) {
+  return xfade(this, pos, b);
+};

test/__snapshots__/examples.test.mjs.snap

@@ -5235,6 +5235,51 @@ exports[`runs examples > example "withValue" example index 0 1`] = `
 ]
 `;
 
+exports[`runs examples > example "xfade" example index 0 1`] = `
+[
+  "[ 0/1 → 1/8 | s:hh gain:0 ]",
+  "[ 0/1 → 1/2 | s:bd gain:1 ]",
+  "[ 1/8 → 1/4 | s:hh gain:0 ]",
+  "[ 1/4 → 3/8 | s:hh gain:0 ]",
+  "[ 3/8 → 1/2 | s:hh gain:0 ]",
+  "[ 1/2 → 5/8 | s:hh gain:0 ]",
+  "[ 1/2 → 1/1 | s:bd gain:1 ]",
+  "[ 5/8 → 3/4 | s:hh gain:0 ]",
+  "[ 3/4 → 7/8 | s:hh gain:0 ]",
+  "[ 7/8 → 1/1 | s:hh gain:0 ]",
+  "[ 1/1 → 9/8 | s:hh gain:0.5 ]",
+  "[ 1/1 → 3/2 | s:bd gain:1 ]",
+  "[ 9/8 → 5/4 | s:hh gain:0.5 ]",
+  "[ 5/4 → 11/8 | s:hh gain:0.5 ]",
+  "[ 11/8 → 3/2 | s:hh gain:0.5 ]",
+  "[ 3/2 → 13/8 | s:hh gain:0.5 ]",
+  "[ 3/2 → 2/1 | s:bd gain:1 ]",
+  "[ 13/8 → 7/4 | s:hh gain:0.5 ]",
+  "[ 7/4 → 15/8 | s:hh gain:0.5 ]",
+  "[ 15/8 → 2/1 | s:hh gain:0.5 ]",
+  "[ 2/1 → 17/8 | s:hh gain:1 ]",
+  "[ 2/1 → 5/2 | s:bd gain:1 ]",
+  "[ 17/8 → 9/4 | s:hh gain:1 ]",
+  "[ 9/4 → 19/8 | s:hh gain:1 ]",
+  "[ 19/8 → 5/2 | s:hh gain:1 ]",
+  "[ 5/2 → 21/8 | s:hh gain:1 ]",
+  "[ 5/2 → 3/1 | s:bd gain:1 ]",
+  "[ 21/8 → 11/4 | s:hh gain:1 ]",
+  "[ 11/4 → 23/8 | s:hh gain:1 ]",
+  "[ 23/8 → 3/1 | s:hh gain:1 ]",
+  "[ 3/1 → 25/8 | s:hh gain:1 ]",
+  "[ 3/1 → 7/2 | s:bd gain:0.5 ]",
+  "[ 25/8 → 13/4 | s:hh gain:1 ]",
+  "[ 13/4 → 27/8 | s:hh gain:1 ]",
+  "[ 27/8 → 7/2 | s:hh gain:1 ]",
+  "[ 7/2 → 29/8 | s:hh gain:1 ]",
+  "[ 7/2 → 4/1 | s:bd gain:0.5 ]",
+  "[ 29/8 → 15/4 | s:hh gain:1 ]",
+  "[ 15/4 → 31/8 | s:hh gain:1 ]",
+  "[ 31/8 → 4/1 | s:hh gain:1 ]",
+]
+`;
+
 exports[`runs examples > example "zoom" example index 0 1`] = `
 [
   "[ 0/1 → 1/6 | s:hh ]",

website/src/pages/learn/effects.mdx

@@ -156,6 +156,10 @@ There is one filter envelope for each filter type and thus one set of envelope f
 
 <JsDoc client:idle name="postgain" h={0} />
 
+## xfade
+
+<JsDoc client:idle name="xfade" h={0} />
+
 # Panning
 
 ## jux