timeline feature

packages/core/impure.mjs

@@ -0,0 +1,60 @@
+/*
+stateful.mjs - File of shame for stateful, impure and otherwise illegal pattern methods
+Copyright (C) 2025 Strudel contributors - see <https://codeberg.org/uzu/strudel/src/branch/main/packages/core/index.mjs>
+This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details. You should have received a copy of the GNU Affero General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+import { register, reify } from './pattern.mjs';
+
+let timelines = {};
+
+export const reset_timelines = function () {
+  timelines = {};
+};
+
+export const timeline = register(
+  'timeline',
+  function (tpat, pat) {
+    tpat = reify(tpat);
+    const f = function (state) {
+      let scheduler = !!state.controls._cps;
+
+      const timehaps = tpat.query(state);
+      const result = [];
+      for (const timehap of timehaps) {
+        const tlid = timehap.value;
+        const ignore = false;
+        let offset;
+        if (tlid in timelines) {
+          offset = timelines[tlid];
+        } else {
+          const timearc = timehap.wholeOrPart();
+          if (!scheduler || state.span.begin.lt(timearc.midpoint())) {
+            offset = timearc.begin;
+          } else {
+            // Sync to end of timearc if we first see it over halfway into its
+            // timespan. Allows 'cuing up' next timeline when live coding.
+            offset = timearc.end;
+          }
+        }
+        if (scheduler) {
+          // update state
+          timelines[tlid] = offset;
+          const negative = 0 - tlid;
+          if (negative in timelines) {
+            delete timelines[negative];
+          }
+        }
+
+        const pathaps = pat
+          .late(offset)
+          .query(state.setSpan(timehap.part))
+          .map((h) => h.setContext(h.combineContext(timehap)));
+        result.push(...pathaps);
+      }
+      return result;
+    };
+    return new Pattern(f, pat._steps);
+  },
+  false,
+);