Fences join like walls, fence designs, draw runs corner by corner

Joints: line_joint (util.rhai) applies the house-wall rules to fences and
site walls, so pieces never overlap and the depth sort stays clean.
- A corner is closed: the thicker piece (or, if equal, the one along
  world x) runs through, and the other stops at its face.
- On a straight run, two pieces share one post.
- At a T, the stem stops at the other piece's face without a post of its
  own.
- A fence that ends at a site or house wall stops at the wall's face.

Fence designs (prop style): mesh, wooden boards, steel bars, mesh on a
stone base, cobble wall, and brick wall with pillars. Board, stone and
brick joints are drawn on the face turned to the viewer. Brick pillars
are separate sprites.

Studio: line prefabs (walls, fences, hedges, roads) can be drawn as a
run by clicking corner after corner. Double-click or Enter ends the run,
clicking the first corner closes it, and Backspace drops the last
corner. A run is one undo step. A drag still draws one piece. Corners
and ends snap onto the ends and lines of the pieces they meet, and a
marker shows where the next corner will snap.

The house demo gets a brick front wall with gate pillars and wooden side
fences in place of the old east fence, which ran over the road. Tests
cover every design's corners, Ts, straight runs and wall stops, with no
depth-sort cycles in any rotation, plus site walls. check_studio draws
and closes a fence run, undoes it in one step, snaps a dragged spur,
and picks a design.

studio/studio.js

@@ -111,6 +111,97 @@
     return [{ pts: planePts(worldOf(sm.host, sm.u - sm.hw, 0), worldOf(sm.host, sm.u + sm.hw, 0), sm.z + z0, sm.z + z0 + h), cls: "st-plane" }];
   }
 
+  // ------------------------------------------------------------ drawing runs of walls and fences
+  // Line prefabs (walls, fences, hedges, roads) are drawn corner by corner. Corners snap onto the
+  // ends and lines of the pieces already there, so the scripts join them (line_joint in util.rhai).
+  var chain = null;   // a run being drawn: { m, z, pts: [[x, y], ...] }
+  // metres per screen pixel around a pointer event
+  function pxM(e) { var a = S.view.toWorld(e.clientX, e.clientY, 0), b = S.view.toWorld(e.clientX + 10, e.clientY, 0); return Math.hypot(b[0] - a[0], b[1] - a[1]) / 10; }
+  function linePieces(z) {
+    return S.doc.objects.filter(function (o) { var m = prefab(o.type); return !o.hidden && m && m.shape === "line" && Math.abs((o.z || 0) - z) < 0.5; }).map(function (o) {
+      var L = (+propOf(o, "w") || 0) / 2;
+      return { o: o, a: worldOf(o, -L, 0), b: worldOf(o, L, 0), ax: qOf(o.rot) % 2 === 0 };
+    });
+  }
+  // where a corner goes for pointer world point w: with `from` (the previous corner) the piece keeps
+  // to x or y and its far end snaps onto an end or the line of a piece it meets (or the run's own
+  // corners), else onto the grid; without, onto the nearest end, else onto a line, else the grid
+  function snapCorner(w, z, from, R) {
+    var pcs = linePieces(z), own = chain ? chain.pts : [], best = null, i;
+    if (!from) {
+      pcs.forEach(function (p) {
+        [p.a, p.b].forEach(function (q) { var d = Math.hypot(q[0] - w[0], q[1] - w[1]); if (d < R && (!best || d < best.d)) best = { d: d, p: q }; });
+      });
+      if (best) return [r3(best.p[0]), r3(best.p[1])];
+      pcs.forEach(function (p) {
+        var l = localOf(p.o, w[0], w[1]), L = (+propOf(p.o, "w") || 0) / 2;
+        if (Math.abs(l[0]) <= L && Math.abs(l[1]) < R && (!best || Math.abs(l[1]) < best.d)) best = { d: Math.abs(l[1]), p: worldOf(p.o, Math.max(-L, Math.min(L, snap(l[0]))), 0) };
+      });
+      return best ? [r3(best.p[0]), r3(best.p[1])] : [snap(w[0]), snap(w[1])];
+    }
+    var ax = Math.abs(w[0] - from[0]) >= Math.abs(w[1] - from[1]), k = ax ? 0 : 1, lk = 1 - k;
+    var f = w[k], fix = from[lk], cands = [];
+    pcs.forEach(function (p) {
+      if (p.ax === ax) {
+        // in line with this piece: its ends
+        if (Math.abs(p.a[lk] - fix) < 0.01) { cands.push(p.a[k]); cands.push(p.b[k]); }
+      } else {
+        // across this piece: its centre line, where it spans our line
+        var lo = Math.min(p.a[lk], p.b[lk]), hi = Math.max(p.a[lk], p.b[lk]);
+        if (fix >= lo - 1e-6 && fix <= hi + 1e-6) cands.push(p.a[k]);
+      }
+    });
+    for (i = 0; i < own.length; i++) if (Math.abs(own[i][lk] - fix) < 0.01) cands.push(own[i][k]);
+    cands.forEach(function (c) { var d = Math.abs(c - f); if (Math.abs(c - from[k]) > 0.05 && d < R && (!best || d < best.d)) best = { d: d, c: c }; });
+    var out = [0, 0];
+    out[k] = r3(best ? best.c : snap(f)); out[lk] = fix;
+    return out;
+  }
+  // the preview of one piece from p to q: its footprint, and its face when it has a height
+  function pieceGhost(m, p, q, z) {
+    var th = +(defOf(m, "t") || defOf(m, "d")) || 0.3, h = +defOf(m, "h") || 0, ax = Math.abs(q[1] - p[1]) < 1e-9;
+    var x0 = Math.min(p[0], q[0]), x1 = Math.max(p[0], q[0]), y0 = Math.min(p[1], q[1]), y1 = Math.max(p[1], q[1]);
+    var out = [{ pts: ax ? rectPts(x0, y0 - th / 2, x1, y0 + th / 2, z) : rectPts(x0 - th / 2, y0, x0 + th / 2, y1, z) }];
+    if (h > 0) out.push({ pts: planePts(p, q, z, z + h), cls: "st-plane" });
+    return out;
+  }
+  function cornerMark(p, z) { return { pts: rectPts(p[0] - 0.18, p[1] - 0.18, p[0] + 0.18, p[1] + 0.18, z), cls: "st-plane" }; }
+  function runLength(pts) { var L = 0; for (var i = 1; i < pts.length; i++) L += Math.hypot(pts[i][0] - pts[i - 1][0], pts[i][1] - pts[i - 1][1]); return L; }
+  function drawChain(e) {
+    var c = chain, last = c.pts[c.pts.length - 1], q = snapCorner(worldAt(e, c.z), c.z, last, 12 * pxM(e)), polys = [], i;
+    for (i = 1; i < c.pts.length; i++) Array.prototype.push.apply(polys, pieceGhost(c.m, c.pts[i - 1], c.pts[i], c.z));
+    if (Math.hypot(q[0] - last[0], q[1] - last[1]) > 0.05) Array.prototype.push.apply(polys, pieceGhost(c.m, last, q, c.z));
+    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);
+    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  ·  " +
+      (closes ? "click to close the run" : "click the next corner · double-click or Enter to finish · click the first corner to close") + " · Backspace undoes a corner · Esc cancels");
+  }
+  // the pieces of a run as add ops (pieces longer than the prefab allows are split)
+  function runOps(m, pts, z) {
+    var ops = [], max = +((m.props || []).filter(function (d) { return d.key === "w"; })[0] || {}).max || 1e9;
+    for (var i = 1; i < pts.length; i++) {
+      var p = pts[i - 1], q = pts[i], L = Math.hypot(q[0] - p[0], q[1] - p[1]), n = Math.ceil(L / max - 1e-9), ax = Math.abs(q[1] - p[1]) < 1e-9;
+      if (L < 0.05) continue;
+      for (var j = 0; j < n; j++) {
+        var t = (j + 0.5) / n, add = { op: "add", type: m.type, x: r3(p[0] + (q[0] - p[0]) * t), y: r3(p[1] + (q[1] - p[1]) * t), rot: ax ? 0 : 90, props: { w: clampProp(m, "w", L / n) } };
+        if (z) add.z = z;
+        ops.push(add);
+      }
+    }
+    return ops;
+  }
+  function finishChain(keep) {
+    var c = chain; chain = null; ghost(null);
+    if (!c) return;
+    var ops = runOps(c.m, c.pts, c.z);
+    if (ops.length) {
+      var L = runLength(c.pts);
+      opList(ops).then(function (r) { if (r) toast(c.m.label + ": " + ops.length + " piece" + (ops.length === 1 ? "" : "s") + ", " + L.toFixed(1) + " m · Ctrl+Z takes the run back"); });
+    }
+    if (keep) setPlacing(c.m.type); else setPlacing(null);
+  }
+
   // ------------------------------------------------------------ server state
   function takeState(r) {
     if (r.doc) S.doc = r.doc;
@@ -182,7 +273,8 @@
         down: function (e, hit) {
           if (S.placing) {
             var pm = pmeta(S.placing), z = placeZ(pm), a = worldAt(e, z);
-            tool = { m: pm, z: z, a: [snap(a[0]), snap(a[1])], b: null };
+            a = pm.shape === "line" ? snapCorner(a, z, chain ? chain.pts[chain.pts.length - 1] : null, 12 * pxM(e)) : [snap(a[0]), snap(a[1])];
+            tool = { m: pm, z: z, a: a, b: null };
             return true;
           }
           if (!hit.obj) return false;
@@ -226,7 +318,8 @@
           } else if (d.dx || d.dy) moveWith(d.id, d.dx, d.dy, d.carry);
           else S.view.refresh();
         },
-        cancel: function () { if (drag && drag.els) S.view.refresh(); drag = null; tool = null; ghost(null); }
+        cancel: function () { if (drag && drag.els) S.view.refresh(); drag = null; tool = null; ghost(null); },
+        dblclick: function (e) { if (!chain) return false; finishChain(e.shiftKey); return true; }
       }
     });
     window.__studio = { S: S, view: S.view, op: op, select: select, reloadAll: reloadAll, toast: toast, api: api, obj: obj, snapStep: snapStep, ready: true };
@@ -244,6 +337,8 @@
   // the hover preview while placing a window or door: where on which wall it goes
   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 || !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);
@@ -261,7 +356,8 @@
   }
   function drawTool(e) {
     var t = tool, m = t.m, w = worldAt(e, t.z), z = t.z, polys = [];
-    t.b = [snap(w[0]), snap(w[1])];
+    if (chain) { drawChain(e); return; }
+    t.b = m.shape === "line" ? snapCorner(w, z, t.a, 12 * pxM(e)) : [snap(w[0]), snap(w[1])];
     if (m.shape !== "line" && m.shape !== "rect") return;
     var g = toolGeom(t);
     if (g.line) {
@@ -283,6 +379,22 @@
   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") {
+      // 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));
+        if (Math.hypot(q[0] - last[0], q[1] - last[1]) < 0.05) return;
+        chain.pts.push(q);
+        if (chain.pts.length > 3 && Math.hypot(q[0] - chain.pts[0][0], q[1] - chain.pts[0][1]) < 1e-6) finishChain(keep);
+        else drawChain(e);
+        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);
+      opList(ops).then(function (r) { if (r) toast(m.label + " added" + (keep ? "" : " · Shift to draw several")); });
+      if (!keep) setPlacing(null);
+      return;
+    }
     if (m === ROOM) {
       if (!g || !g.ok) { toast("Drag a rectangle on the map to draw a room"); setPlacing(m.type); return; }
       var fm = prefab("floor"), ops = roomWalls(g.x0, g.y0, g.x1, g.y1, t.z);
@@ -326,7 +438,7 @@
     return out;
   }
   function setPlacing(kind) {
-    S.placing = kind; tool = null;
+    S.placing = kind; tool = null; chain = null;
     if (S.view) ghost(null);
     document.querySelector(".st-centre").classList.toggle("st-placing", !!kind);
     Array.prototype.forEach.call(document.querySelectorAll(".st-tile"), function (b) { b.setAttribute("aria-pressed", String(b.getAttribute("data-type") === kind)); });
@@ -335,7 +447,7 @@
       var m = pmeta(kind), lab = m ? m.label : kind;
       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: " + lab + " (a click gives the default length)  ·  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 === "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;
@@ -397,7 +509,9 @@
     var k = e.key, ctrl = e.ctrlKey || e.metaKey;
     if (ctrl && (k === "z" || k === "Z")) { if (e.shiftKey) redo(); else undo(); return true; }
     if (ctrl && (k === "y" || k === "Y")) { redo(); return true; }
-    if (k === "Escape") { if (S.placing) setPlacing(null); else select(null); return true; }
+    if (chain && k === "Enter") { finishChain(e.shiftKey); return true; }
+    if (chain && k === "Backspace") { chain.pts.pop(); if (!chain.pts.length) { chain = null; ghost(null); setPlacing(S.placing); } else ghost(null); return true; }
+    if (k === "Escape") { if (chain) { chain = null; ghost(null); setPlacing(S.placing); } else if (S.placing) setPlacing(null); else select(null); return true; }
     if (!S.sel) return false;
     if (k === "Delete" || k === "Backspace") { remove(S.sel); return true; }
     if (ctrl && (k === "d" || k === "D")) { duplicate(S.sel); return true; }