From c2535c6e656b2e838e08f918aca94db10b566653 Mon Sep 17 00:00:00 2001
From: Daddy32 <daddy@autistici.org>
Date: Fri, 12 Dec 2025 19:32:42 +0100
Subject: [PATCH] Limit chain preview to max link distance

---
 main.js | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/main.js b/main.js
index 71b717b..59c6bfc 100644
--- a/main.js
+++ b/main.js
@@ -25,6 +25,7 @@
       lineWidth: 3,
       rope: true,
       renderType: "line",
+      maxLengthMultiplier: 3.1,
     },
   };
 
@@ -45,6 +46,7 @@
           lineWidth: 3,
           rope: true,
           renderType: "line",
+          maxLengthMultiplier: 3.2,
         },
       },
       createBodies: (w, h) => [
@@ -91,6 +93,7 @@
           lineWidth: 4,
           rope: false,
           renderType: "spring",
+          maxLengthMultiplier: 6.7,
         },
       },
       createBodies: (w, h) => [
@@ -130,6 +133,7 @@
           lineWidth: 3,
           rope: false,
           renderType: "line",
+          maxLengthMultiplier: 16.8,
         },
       },
       createBodies: (w, h) => {
@@ -274,6 +278,15 @@
     pointer: null,
   };
 
+  const getMaxLinkDistance = () => {
+    const linkCfg = config.link || {};
+    if (Number.isFinite(linkCfg.maxLinkLength)) {
+      return linkCfg.maxLinkLength;
+    }
+    const mult = linkCfg.maxLengthMultiplier ?? 3;
+    return mult * config.ballRadius;
+  };
+
   const spawnBall = () => {
     if (gameOver) return;
     const color =
@@ -516,6 +529,11 @@
       return;
     }
     if (body.plugin.color !== chain.color) return;
+    const maxLinkDist = getMaxLinkDistance();
+    const dist = Vector.magnitude(
+      Vector.sub(chain.bodies[chain.bodies.length - 1].position, body.position),
+    );
+    if (dist > maxLinkDist) return;
     addToChain(body);
   };
 
@@ -644,13 +662,29 @@
     if (!chain.active || !chain.pointer || chain.bodies.length === 0) return;
     const last = chain.bodies[chain.bodies.length - 1];
     const ctx = render.context;
+    const maxLinkDist = getMaxLinkDistance();
+    const delta = Vector.sub(chain.pointer, last.position);
+    const dist = Vector.magnitude(delta);
+    // Pull back the preview line slightly so it does not suggest a link will land on a too-distant ball.
+    const previewMargin = config.ballRadius;
+    const cappedDist = Math.max(
+      0,
+      Math.min(dist, Math.max(0, maxLinkDist - previewMargin)),
+    );
+    const safeTarget =
+      dist > 0
+        ? Vector.add(
+            last.position,
+            Vector.mult(Vector.normalise(delta), cappedDist),
+          )
+        : chain.pointer;
     ctx.save();
     ctx.strokeStyle = chain.color || "#fff";
     ctx.lineWidth = 3;
     ctx.setLineDash([6, 6]);
     ctx.beginPath();
     ctx.moveTo(last.position.x, last.position.y);
-    ctx.lineTo(chain.pointer.x, chain.pointer.y);
+    ctx.lineTo(safeTarget.x, safeTarget.y);
     ctx.stroke();
     ctx.restore();
   });