Routes: movers along waypoints (roadmap 8)

New route prefab (routes.rhai): cars, buses, motorbikes, cyclists, people,
deer or elephants move along waypoints, round a loop or there and back.
Each way keeps to the left of the line (or right), corners are rounded
into pieces of at most 45 degrees; there-and-back routes become loops with
U-turns, so the two directions never share a strip.

Engine: Prim::Travel / sprite.begin_travel / script travel(a, b, dur,
windows) ... end(): the mover is drawn at a piece's start and slides to
its end while it is on that piece, hidden otherwise. The renderer writes
keyframes per piece (named by a hash of their content) into one <style>
per view. Each piece is its own sprite with the lane strip as its sort
extent (ext_reset), mitred at the corners, so movers pass in front of and
behind trees, lamps and houses. Movers that look alike and never meet on
a piece share one drawing. iso-travel pauses (not hides) in still,
reduced-motion and ghosted views.

Studio: meta shape "path" draws point by point (snapping like runs) and
saves one object with pts; ending on the first point closes the loop.
MCP: pts in the object schema, route guidance.

Demos: streets gets traffic round the block, a bus, motorbikes, cyclists
and strolling people (replacing the one-axis cars); country gets cars on
the lane.

Tests: Rust 79 (each mover on exactly one piece at every moment, in every
rotation), Studio 125, web 99.

studio/studio.js

@@ -209,6 +209,12 @@
     polys.push(cornerMark(c.pts[0], c.z));
     var closes = c.pts.length > 2 && Math.hypot(q[0] - c.pts[0][0], q[1] - c.pts[0][1]) < 1e-6;
     var n = c.pts.length - 1 + (Math.hypot(q[0] - last[0], q[1] - last[1]) > 0.05 ? 1 : 0);
+    if (c.m.shape === "path") {
+      ghost(polys, c.m.label + ": " + (n + 1) + " points, " + (runLength(c.pts) + Math.hypot(q[0] - last[0], q[1] - last[1])).toFixed(1) + " m  ·  " +
+        (closes ? "click to close the loop" : "click the next point · double-click or Enter to finish (there and back) · click the first point for a loop") +
+        " · diagonals at 45°, Ctrl: any angle · Backspace undoes a point · Esc cancels");
+      return;
+    }
     ghost(polys, c.m.label + ": " + n + " piece" + (n === 1 ? "" : "s") + ", " + (runLength(c.pts) + Math.hypot(q[0] - last[0], q[1] - last[1])).toFixed(1) + " m" +
       (c.m.corner ? ", corners rounded" : "") + "  ·  " +
       (closes ? "click to close the run" : "click the next corner · double-click or Enter to finish · click the first corner to close") +
@@ -223,6 +229,21 @@
     if (!m.directed) return ax ? 0 : 90;
     return ax ? (q[0] >= p[0] ? 0 : 180) : (q[1] >= p[1] ? 90 : 270);
   }
+  // prefabs drawn corner by corner: "line" pieces (walls, fences, roads: one object per piece) and
+  // "path" objects (routes: one object whose pts are the points clicked)
+  function isRun(m) { return !!m && (m.shape === "line" || m.shape === "path"); }
+  // the add op of a path object through world points: x, y in the middle of them, pts relative
+  // to it; ending on the first point closes it (props.closed, when the prefab has that prop)
+  function pathOp(m, pts, z) {
+    var p = pts.slice(), closed = p.length > 3 && Math.hypot(p[p.length - 1][0] - p[0][0], p[p.length - 1][1] - p[0][1]) < 1e-6;
+    if (closed) p.pop();
+    var xs = p.map(function (q) { return q[0]; }), ys = p.map(function (q) { return q[1]; });
+    var cx = r3((Math.min.apply(null, xs) + Math.max.apply(null, xs)) / 2), cy = r3((Math.min.apply(null, ys) + Math.max.apply(null, ys)) / 2);
+    var add = { op: "add", type: m.type, x: cx, y: cy, pts: p.map(function (q) { return [r3(q[0] - cx), r3(q[1] - cy)]; }), props: {} };
+    if ((m.props || []).some(function (d) { return d.key === "closed"; })) add.props.closed = closed;
+    if (z) add.z = z;
+    return add;
+  }
   // Ctrl (Cmd) frees the angle of the piece being drawn; directed lines (conveyors) keep to the axes
   function freeAngle(m, e) { return !!(e && (e.ctrlKey || e.metaKey) && !m.directed); }
   // the corners of a run rounded by the prefab's corner piece (roads: curves of up to its default
@@ -276,6 +297,14 @@
   function finishChain(keep) {
     var c = chain; chain = null; ghost(null);
     if (!c) return;
+    if (c.m.shape === "path") {
+      if (c.pts.length >= 2) {
+        var po = pathOp(c.m, c.pts, c.z), np = po.pts.length, closed = !!(po.props && po.props.closed);
+        op(po).then(function (r) { if (r) toast(c.m.label + ": " + np + " points, " + runLength(c.pts).toFixed(1) + " m" + (closed ? ", a loop" : ", there and back") + " · Ctrl+Z takes it back"); });
+      }
+      if (keep) setPlacing(c.m.type); else setPlacing(null);
+      return;
+    }
     var ops = runOps(c.m, c.pts, c.z);
     if (ops.length) {
       var L = runLength(c.pts);
@@ -363,7 +392,7 @@
         down: function (e, hit) {
           if (S.placing) {
             var pm = pmeta(S.placing), z = placeZ(pm), a = worldAt(e, z);
-            a = pm.shape === "line" ? snapCorner(a, z, chain ? chain.pts[chain.pts.length - 1] : null, 12 * pxM(e), freeAngle(pm, e)) : [snap(a[0]), snap(a[1])];
+            a = isRun(pm) ? snapCorner(a, z, chain ? chain.pts[chain.pts.length - 1] : null, 12 * pxM(e), freeAngle(pm, e)) : [snap(a[0]), snap(a[1])];
             tool = { m: pm, z: z, a: a, b: null };
             return true;
           }
@@ -443,7 +472,7 @@
   function hoverPlacing(e) {
     var m = pmeta(S.placing);
     if (chain) { drawChain(e); return; }
-    if (m && m.shape === "line") { var z0 = placeZ(m); ghost([cornerMark(snapCorner(worldAt(e, z0), z0, null, 12 * pxM(e)), z0)]); return; }
+    if (m && isRun(m)) { var z0 = placeZ(m); ghost([cornerMark(snapCorner(worldAt(e, z0), z0, null, 12 * pxM(e)), z0)]); return; }
     if (!m || !m.mount || !m.mount.length) return;
     var z = placeZ(m), sm = snapMount(m, worldAt(e, z), z, null, defOf(m, "w"));
     ghost(sm ? mountGhost(m, sm) : null);
@@ -452,7 +481,7 @@
   // diagonal by snapCorner), "rect" prefabs (and rooms) fill the rectangle
   function toolGeom(t) {
     var a = t.a, b = t.b || t.a, dx = b[0] - a[0], dy = b[1] - a[1];
-    if (t.m.shape === "line") {
+    if (isRun(t.m)) {
       var L = Math.hypot(dx, dy);
       return { line: true, len: L, a: a, b: b, x: (a[0] + b[0]) / 2, y: (a[1] + b[1]) / 2, ok: L >= 0.25, rot: lineRot(t.m, a, b) };
     }
@@ -462,8 +491,8 @@
   function drawTool(e) {
     var t = tool, m = t.m, w = worldAt(e, t.z), z = t.z, polys = [];
     if (chain) { drawChain(e); return; }
-    t.b = m.shape === "line" ? snapCorner(w, z, t.a, 12 * pxM(e), freeAngle(m, e)) : [snap(w[0]), snap(w[1])];
-    if (m.shape !== "line" && m.shape !== "rect") return;
+    t.b = isRun(m) ? snapCorner(w, z, t.a, 12 * pxM(e), freeAngle(m, e)) : [snap(w[0]), snap(w[1])];
+    if (!isRun(m) && m.shape !== "rect") return;
     var g = toolGeom(t);
     if (g.line) {
       polys = pieceGhost(m, g.a, g.b, z);
@@ -483,7 +512,7 @@
   function finishTool(t, e) {
     var m = t.m, keep = e.shiftKey, g = t.b ? toolGeom(t) : null, add;
     var at = worldAt(e, t.z), p = [snap(at[0]), snap(at[1])];
-    if (m.shape === "line") {
+    if (isRun(m)) {
       // a run: a click starts it, each click (or drag) adds a corner, the first corner closes it
       if (chain) {
         var last = chain.pts[chain.pts.length - 1], q = snapCorner(at, t.z, last, 12 * pxM(e), freeAngle(m, e));
@@ -494,7 +523,7 @@
         return;
       }
       if (!g || !g.ok) { chain = { m: m, z: t.z, pts: [t.a] }; drawChain(e); return; }
-      var ops = runOps(m, [t.a, t.b], t.z);
+      var ops = m.shape === "path" ? [pathOp(m, [t.a, t.b], t.z)] : runOps(m, [t.a, t.b], t.z);
       opList(ops).then(function (r) { if (r) toast(m.label + " added" + (keep ? "" : " · Shift to draw several")); });
       if (!keep) setPlacing(null);
       return;
@@ -552,6 +581,7 @@
       h.textContent = m === ROOM ? "Drag a rectangle on the map: a room (floor and walls)  ·  Esc to stop"
         : m && m.mount && m.mount.length ? "Click on a wall to place: " + lab + "  ·  Esc to stop"
         : m && m.shape === "line" ? "Drag along the map to draw one " + lab + ", or click corner after corner for a run (double-click or Enter ends it, the first corner closes it); ends snap onto walls and fences  ·  Esc to stop"
+        : m && m.shape === "path" ? "Click point after point on the map for the " + lab + " (double-click or Enter ends it; the first point again makes a loop); points snap onto road and wall ends  ·  Esc to stop"
         : m && m.shape === "rect" ? "Drag a rectangle on the map: " + lab + " (a click gives the default size)  ·  Esc to stop"
         : "Click on the map to place: " + lab + "  ·  Esc to stop";
       h.hidden = false;