From fb56db605f0bf5613485ba48c169a78507e5f68e Mon Sep 17 00:00:00 2001
From: Daddy32 <daddy@autistici.org>
Date: Fri, 12 Dec 2025 18:25:12 +0100
Subject: [PATCH] Tighten rope links and expose render type per scene

---
 main.js | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 57 insertions(+), 4 deletions(-)

diff --git a/main.js b/main.js
index 9d2b96c..bd35e3e 100644
--- a/main.js
+++ b/main.js
@@ -17,7 +17,14 @@
     minChain: 3,
     palette: ["#ff595e", "#ffca3a", "#8ac926", "#1982c4", "#6a4c93"],
     ballRadius: 18,
-    link: { stiffness: 0.6, lengthScale: 0.5, damping: 0.08, lineWidth: 3 },
+    link: {
+      stiffness: 0.85,
+      lengthScale: 1.05, // max stretch factor; slack below this
+      damping: 0.08,
+      lineWidth: 3,
+      rope: true,
+      renderType: "line",
+    },
   };
 
   const scenes = [
@@ -30,7 +37,14 @@
         minChain: 3,
         palette: ["#ff595e", "#ffca3a", "#8ac926", "#1982c4", "#6a4c93"],
         ballRadius: 38,
-        link: { stiffness: 0.6, lengthScale: 0.5, damping: 0.08, lineWidth: 3 },
+        link: {
+          stiffness: 0.85,
+          lengthScale: 1.05,
+          damping: 0.08,
+          lineWidth: 3,
+          rope: true,
+          renderType: "line",
+        },
       },
       createBodies: (w, h) => [
         Bodies.rectangle(w / 2, h + 40, w, 80, {
@@ -58,7 +72,14 @@
         minChain: 3,
         palette: ["#fb7185", "#fbbf24", "#34d399", "#38bdf8"],
         ballRadius: 22,
-        link: { stiffness: 0.6, lengthScale: 1.2, damping: 0.01, lineWidth: 4 },
+        link: {
+          stiffness: 0.6,
+          lengthScale: 1,
+          damping: 0.01,
+          lineWidth: 4,
+          rope: false,
+          renderType: "spring",
+        },
       },
       createBodies: (w, h) => [
         Bodies.rectangle(w / 2, h + 50, w, 100, {
@@ -90,7 +111,14 @@
         minChain: 3,
         palette: ["#e879f9", "#38bdf8", "#f97316", "#22c55e"],
         ballRadius: 16,
-        link: { stiffness: 1, lengthScale: 0.85, damping: 0.15, lineWidth: 3 },
+        link: {
+          stiffness: 1,
+          lengthScale: 0.85,
+          damping: 0.15,
+          lineWidth: 3,
+          rope: false,
+          renderType: "line",
+        },
       },
       createBodies: (w, h) => {
         const bodies = [
@@ -368,8 +396,15 @@
       render: {
         strokeStyle: chain.color,
         lineWidth: linkCfg.lineWidth ?? 3,
+        type: linkCfg.renderType || "line",
       },
     });
+    constraint.plugin = {
+      restLength: dist * (linkCfg.lengthScale ?? 1),
+      rope: linkCfg.rope ?? false,
+      baseStiffness: linkCfg.stiffness ?? 0.9,
+      maxLength: dist * (linkCfg.lengthScale ?? 1),
+    };
     chain.constraints.push(constraint);
     chain.bodies.push(body);
     setHighlight(body, true);
@@ -565,6 +600,24 @@
     });
   });
 
+  Events.on(engine, "beforeUpdate", () => {
+    // Rope-like constraint handling: allow shortening without push-back, tension when stretched.
+    chain.constraints.forEach((c) => {
+      if (!c.plugin || !c.plugin.rope) return;
+      const current = Vector.magnitude(
+        Vector.sub(c.bodyA.position, c.bodyB.position),
+      );
+      const maxLen = c.plugin.maxLength ?? c.length;
+      if (current <= maxLen) {
+        c.length = current;
+        c.stiffness = 0;
+      } else {
+        c.length = maxLen;
+        c.stiffness = c.plugin.baseStiffness ?? c.stiffness;
+      }
+    });
+  });
+
   Events.on(render, "afterRender", () => {
     if (!chain.active || !chain.pointer || chain.bodies.length === 0) return;
     const last = chain.bodies[chain.bodies.length - 1];