From daf26af006ee0de5a5597dc91e3d81d196e5dde5 Mon Sep 17 00:00:00 2001
From: liabru <liabru@brm.io>
Date: Tue, 25 Apr 2017 23:48:37 +0100
Subject: [PATCH] implemented constraint warming

---
 src/constraint/Constraint.js | 28 +++++++++++++++++++++++++---
 src/core/Engine.js           |  1 +
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/constraint/Constraint.js b/src/constraint/Constraint.js
index 730e2f0..627353a 100644
--- a/src/constraint/Constraint.js
+++ b/src/constraint/Constraint.js
@@ -72,6 +72,27 @@ var Common = require('../core/Common');
         return constraint;
     };
 
+    /**
+     * Prepares for solving by constraint warming.
+     * @private
+     * @method preSolveAll
+     * @param {body[]} bodies
+     */
+    Constraint.preSolveAll = function(bodies) {
+        for (var i = 0; i < bodies.length; i += 1) {
+            var body = bodies[i],
+                impulse = body.constraintImpulse;
+
+            if (body.isStatic || (impulse.x === 0 && impulse.y === 0 && impulse.angle === 0)) {
+                continue;
+            }
+
+            body.position.x += impulse.x;
+            body.position.y += impulse.y;
+            body.angle += impulse.angle;
+        }
+    };
+
     /**
      * Solves all constraints in a list of collisions.
      * @private
@@ -247,9 +268,10 @@ var Common = require('../core/Common');
                 Bounds.update(part.bounds, part.vertices, body.velocity);
             }
 
-            impulse.angle = 0;
-            impulse.x = 0;
-            impulse.y = 0;
+            // dampen the cached impulse for warming next step
+            impulse.angle *= Constraint._warming;
+            impulse.x *= Constraint._warming;
+            impulse.y *= Constraint._warming;
         }
     };
 
diff --git a/src/core/Engine.js b/src/core/Engine.js
index 33885e9..42c9de1 100644
--- a/src/core/Engine.js
+++ b/src/core/Engine.js
@@ -150,6 +150,7 @@ var Body = require('../body/Body');
         _bodiesUpdate(allBodies, delta, timing.timeScale, correction, world.bounds);
 
         // update all constraints
+        Constraint.preSolveAll(allBodies);
         for (i = 0; i < engine.constraintIterations; i++) {
             Constraint.solveAll(allConstraints, timing.timeScale);
         }