From d58db2e6f2c010f3298ab9d5942282fa31a1eb19 Mon Sep 17 00:00:00 2001
From: Daniel Chappuis <chappuis.daniel>
Date: Thu, 27 Jun 2013 19:53:13 +0200
Subject: [PATCH] Remove the gravity from the rigid body external force and
 allow the user to enable/disable the gravity for each body

---
 src/body/RigidBody.cpp       |  3 ++-
 src/body/RigidBody.h         | 19 +++++++++++++++++++
 src/engine/DynamicsWorld.cpp | 32 ++++++++------------------------
 src/engine/DynamicsWorld.h   |  3 ---
 4 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/src/body/RigidBody.cpp b/src/body/RigidBody.cpp
index 40139aff..5b2022bd 100644
--- a/src/body/RigidBody.cpp
+++ b/src/body/RigidBody.cpp
@@ -35,7 +35,8 @@ using namespace reactphysics3d;
                       CollisionShape *collisionShape, bodyindex id)
            : CollisionBody(transform, collisionShape, id), mInertiaTensorLocal(inertiaTensorLocal),
              mMass(mass), mInertiaTensorLocalInverse(inertiaTensorLocal.getInverse()),
-             mMassInverse(decimal(1.0) / mass), mFrictionCoefficient(DEFAULT_FRICTION_COEFFICIENT) {
+             mMassInverse(decimal(1.0) / mass), mFrictionCoefficient(DEFAULT_FRICTION_COEFFICIENT),
+             mIsGravityEnabled(true) {
 
     mRestitution = decimal(1.0);
 
diff --git a/src/body/RigidBody.h b/src/body/RigidBody.h
index 1f340961..66a3f70c 100644
--- a/src/body/RigidBody.h
+++ b/src/body/RigidBody.h
@@ -79,6 +79,9 @@ class RigidBody : public CollisionBody {
         /// Friction coefficient
         decimal mFrictionCoefficient;
 
+        /// True if the gravity needs to be applied to this rigid body
+        bool mIsGravityEnabled;
+
         // -------------------- Methods -------------------- //
 
         /// Private copy-constructor
@@ -160,6 +163,12 @@ class RigidBody : public CollisionBody {
 
         /// Set the friction coefficient
         void setFrictionCoefficient(decimal frictionCoefficient);
+
+        /// Return true if the gravity needs to be applied to this rigid body
+        bool isGravityEnabled() const;
+
+        /// Set the variable to know if the gravity is applied to this rigid body
+        void enableGravity(bool isEnabled);
 };
 
 // Method that return the mass of the body
@@ -288,6 +297,16 @@ inline void RigidBody::setFrictionCoefficient(decimal frictionCoefficient) {
     mFrictionCoefficient = frictionCoefficient;
 }
 
+// Return true if the gravity needs to be applied to this rigid body
+inline bool RigidBody::isGravityEnabled() const {
+    return mIsGravityEnabled;
+}
+
+// Set the variable to know if the gravity is applied to this rigid body
+inline void RigidBody::enableGravity(bool isEnabled) {
+    mIsGravityEnabled = isEnabled;
+}
+
 }
 
  #endif
diff --git a/src/engine/DynamicsWorld.cpp b/src/engine/DynamicsWorld.cpp
index 5a7062e0..27a8fc12 100644
--- a/src/engine/DynamicsWorld.cpp
+++ b/src/engine/DynamicsWorld.cpp
@@ -88,9 +88,6 @@ void DynamicsWorld::update() {
     // Compute the time since the last update() call and update the timer
     mTimer.update();
 
-    // Apply the gravity force to all bodies
-    applyGravity();
-
     // While the time accumulator is not empty
     while(mTimer.isPossibleToTakeStep()) {
 
@@ -253,6 +250,14 @@ void DynamicsWorld::integrateRigidBodiesVelocities() {
             mConstrainedAngularVelocities[i] = rigidBody->getAngularVelocity() +
                     dt * rigidBody->getInertiaTensorInverseWorld() * rigidBody->getExternalTorque();
 
+            // If the gravity has to be applied to this rigid body
+            if (rigidBody->isGravityEnabled() && mIsGravityOn) {
+
+                // Integrate the gravity force
+                mConstrainedLinearVelocities[i] += dt * rigidBody->getMassInverse() *
+                                                   rigidBody->getMass() * mGravity;
+            }
+
             // Update the old Transform of the body
             rigidBody->updateOldTransform();
         }
@@ -376,27 +381,6 @@ void DynamicsWorld::cleanupConstrainedVelocitiesArray() {
     mMapBodyToConstrainedVelocityIndex.clear();
 }
 
-// Apply the gravity force to all bodies of the physics world
-void DynamicsWorld::applyGravity() {
-
-    PROFILE("DynamicsWorld::applyGravity()");
-
-    // For each body of the physics world
-    set<RigidBody*>::iterator it;
-    for (it = getRigidBodiesBeginIterator(); it != getRigidBodiesEndIterator(); ++it) {
-
-        RigidBody* rigidBody = dynamic_cast<RigidBody*>(*it);
-        assert(rigidBody != NULL);
-   
-        // If the gravity force is on
-        if(mIsGravityOn) {
-
-            // Apply the current gravity force to the body
-            rigidBody->setExternalForce(rigidBody->getMass() * mGravity);
-        }
-    }
-}
-
 // Create a rigid body into the physics world
 RigidBody* DynamicsWorld::createRigidBody(const Transform& transform, decimal mass,
                                           const Matrix3x3& inertiaTensorLocal,
diff --git a/src/engine/DynamicsWorld.h b/src/engine/DynamicsWorld.h
index d5412971..f911bd08 100644
--- a/src/engine/DynamicsWorld.h
+++ b/src/engine/DynamicsWorld.h
@@ -133,9 +133,6 @@ class DynamicsWorld : public CollisionWorld {
         /// Cleanup the constrained velocities array at each step
         void cleanupConstrainedVelocitiesArray();
 
-        /// Apply the gravity force to all bodies
-        void applyGravity();
-
         /// Reset the boolean movement variable of each body
         void resetBodiesMovementVariable();