refactored sequences, sync and gaps

src/core/draw/sync.typ

@@ -0,0 +1,32 @@
+#import "../utils.typ": get-ctx, set-ctx, is-elmt
+
+#let render(sync) = get-ctx(ctx => {
+  set-ctx(c => {
+    c.sync-ys = ()
+    return c
+  })
+
+  for e in sync.elmts {
+    assert(is-elmt(e), message: "Sync element can only contain chronos elements, found " + repr(e))
+    assert(
+      e.type == "seq",
+      message: "Sync element can only contain sequences, found '" + e.type + "'"
+    )
+
+    set-ctx(c => {
+      c.y = ctx.y
+      return c
+    })
+    (e.draw)(e)
+    set-ctx(c => {
+      c.sync-ys.push(c.y)
+      return c
+    })
+  }
+
+  set-ctx(c => {
+    c.y = calc.min(..c.sync-ys)
+    c.remove("sync-ys")
+    return c
+  })
+})