allow zero-mass kinematic rigid bodies

stephengold · May 18, 2023 · 58f3c53 · 58f3c53
1 parent 13a42bb
commit 58f3c53
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Showing 2 changed files with 22 additions and 26 deletions.
diff --git a/src/main/java/com/jme3/bullet/objects/PhysicsRigidBody.java b/src/main/java/com/jme3/bullet/objects/PhysicsRigidBody.java
@@ -620,9 +620,7 @@ assert getInternalType(objectId) == PcoType.rigid :
             }
         }
 
-        if (mass != massForStatic) {
-            setKinematic(kinematic);
-        }
+        setKinematic(kinematic);
 
         postRebuild();
 
@@ -836,12 +834,6 @@ public void setInverseInertiaLocal(Vector3f inverseInertia) {
      * (default=false)
      */
     public void setKinematic(boolean kinematic) {
-        if (mass == massForStatic) {
-            throw new IllegalStateException(
-                    "Cannot set/clear kinematic mode on a static body!");
-        }
-        assert !isStatic();
-
         this.kinematic = kinematic;
         long objectId = nativeId();
         setKinematic(objectId, kinematic);
@@ -1101,7 +1093,7 @@ public Vector3f totalAppliedTorque(Vector3f storeResult) {
      */
     protected void postRebuild() {
         int flags = collisionFlags();
-        if (mass == massForStatic) {
+        if (mass == massForStatic && !kinematic) {
             flags |= CollisionFlag.STATIC_OBJECT;
         } else {
             flags &= ~CollisionFlag.STATIC_OBJECT;
@@ -1178,17 +1170,17 @@ public void setGravity(Vector3f acceleration) {
     }
 
     /**
-     * Alter this body's mass. Bodies with mass=0 are static. For dynamic
-     * bodies, it is best to keep the mass on the order of 1.
+     * Alter this body's mass. Static bodies have mass=0. For dynamic bodies, it
+     * is best to keep the mass on the order of 1.
      *
-     * @param mass the desired mass (&gt;0) or 0 for a static body (default=1)
+     * @param mass the desired mass (&ge;0, default=1)
      */
     @Override
     public void setMass(float mass) {
         Validate.nonNegative(mass, "mass");
         CollisionShape shape = getCollisionShape();
         assert shape != null;
-        if (mass != massForStatic) {
+        if (mass > massForStatic && !kinematic) {
             validateDynamicShape(shape);
         }
         assert hasAssignedNativeObject();
@@ -1208,7 +1200,7 @@ public void setMass(float mass) {
         updateMassProps(objectId, shape.nativeId(), mass);
 
         int flags = collisionFlags();
-        if (mass == massForStatic) {
+        if (mass == massForStatic && !kinematic) {
             flags |= CollisionFlag.STATIC_OBJECT;
         } else {
             flags &= ~CollisionFlag.STATIC_OBJECT;
@@ -1238,10 +1230,6 @@ public void setPhysicsLocation(Vector3f location) {
      * @return true if the flags are equal, otherwise false
      */
     private boolean checkKinematicFlag() {
-        if (mass == massForStatic) {
-            return true; // TODO
-        }
-
         int flags = collisionFlags();
         boolean nativeKinematicFlag
                 = (flags & CollisionFlag.KINEMATIC_OBJECT) != 0x0;

diff --git a/src/main/native/glue/com_jme3_bullet_objects_PhysicsRigidBody.cpp b/src/main/native/glue/com_jme3_bullet_objects_PhysicsRigidBody.cpp
@@ -663,21 +663,29 @@ JNIEXPORT void JNICALL Java_com_jme3_bullet_objects_PhysicsRigidBody_setKinemati
     btRigidBody * const pBody = reinterpret_cast<btRigidBody *> (bodyId);
     NULL_CHK(pEnv, pBody, "The btRigidBody does not exist.",);
     ASSERT_CHK(pEnv, pBody->getInternalType() & btCollisionObject::CO_RIGID_BODY,);
-    ASSERT_CHK(pEnv, !pBody->isStaticObject(),);
 
     int flags = pBody->getCollisionFlags();
     bool oldValue = pBody->isKinematicObject();
 
-    if (value && !oldValue) { // dynamic -> kinematic
-        flags = flags | btCollisionObject::CF_KINEMATIC_OBJECT;
+    if (value && !oldValue) { // dynamic/static -> kinematic
+        flags &= ~btCollisionObject::CF_STATIC_OBJECT;
+        flags |= btCollisionObject::CF_KINEMATIC_OBJECT;
         pBody->setCollisionFlags(flags);
+
         pBody->setActivationState(DISABLE_DEACTIVATION);
 
-    } else if (oldValue && !value) { // kinematic -> dynamic
-        flags = flags & ~btCollisionObject::CF_KINEMATIC_OBJECT;
+    } else if (oldValue && !value) { // kinematic -> dynamic/static
+        bool zeroMass = (pBody->getMass() == btScalar(0.0));
+        if (zeroMass) {
+            flags |= btCollisionObject::CF_STATIC_OBJECT;
+        }
+        flags &= ~btCollisionObject::CF_KINEMATIC_OBJECT;
         pBody->setCollisionFlags(flags);
-        pBody->activate(true);
-        pBody->forceActivationState(ACTIVE_TAG);
+
+        if (!zeroMass) {
+            pBody->activate(true);
+            pBody->forceActivationState(ACTIVE_TAG);
+        }
     }
 }