fixed sync alignment with unequal elements

fixes #21

src/core/draw/sync.typ

@@ -1,11 +1,17 @@
 #import "/src/core/utils.typ": get-ctx, is-elmt, set-ctx
+#import "/src/cetz.typ": draw
 
 #let render(sync) = get-ctx(ctx => {
   set-ctx(c => {
-    c.sync-ys = ()
+    c.sync = (
+      bottoms: (),
+      starts: (),
+      y: ctx.y
+    )
     return c
   })
 
+  // Compute heights
   for e in sync.elmts {
     assert(is-elmt(e), message: "Sync element can only contain chronos elements, found " + repr(e))
     assert(
@@ -17,16 +23,34 @@
       c.y = ctx.y
       return c
     })
-    (e.draw)(e)
+    draw.hide({
+      (e.draw)(e)
+    })
     set-ctx(c => {
-      c.sync-ys.push(c.y)
+      c.sync.starts.push(c.last-drawn.start-info.y)
+      c.sync.bottoms.push(c.y)
       return c
     })
   }
 
   set-ctx(c => {
-    c.y = calc.min(..c.sync-ys)
-    c.remove("sync-ys")
+    c.sync-y = calc.min(..c.sync.starts)
+    return c
+  })
+
+  // Draw aligned elements
+  for (i, e) in sync.elmts.enumerate() {
+    set-ctx(c => {
+      let dy = c.sync.starts.at(i) - ctx.y
+      c.y = c.sync-y - dy
+      return c
+    })
+    (e.draw)(e)
+  }
+
+  set-ctx(c => {
+    c.y = calc.min(..c.sync.bottoms)
+    c.remove("sync")
     return c
   })
 })