Merge pull request #4104 from AndrewMeadows/inertia

store density in EntityItem instead of mass

examples/html/entityProperties.html

@@ -114,7 +114,7 @@
             var elGravityY = document.getElementById("property-grav-y");
             var elGravityZ = document.getElementById("property-grav-z");
 
-            var elMass = document.getElementById("property-mass");
+            var elDensity = document.getElementById("property-density");
             var elIgnoreForCollisions = document.getElementById("property-ignore-for-collisions");
             var elCollisionsWillMove = document.getElementById("property-collisions-will-move");
             var elLifetime = document.getElementById("property-lifetime");
@@ -219,7 +219,7 @@
                             elGravityY.value = properties.gravity.y.toFixed(2);
                             elGravityZ.value = properties.gravity.z.toFixed(2);
 
-                            elMass.value = properties.mass.toFixed(2);
+                            elDensity.value = properties.density.toFixed(2);
                             elIgnoreForCollisions.checked = properties.ignoreForCollisions;
                             elCollisionsWillMove.checked = properties.collisionsWillMove;
                             elLifetime.value = properties.lifetime;
@@ -356,7 +356,7 @@
             elGravityY.addEventListener('change', gravityChangeFunction);
             elGravityZ.addEventListener('change', gravityChangeFunction);
 
-            elMass.addEventListener('change', createEmitNumberPropertyUpdateFunction('mass'));
+            elDensity.addEventListener('change', createEmitNumberPropertyUpdateFunction('density'));
             elIgnoreForCollisions.addEventListener('change', createEmitCheckedPropertyUpdateFunction('ignoreForCollisions'));
             elCollisionsWillMove.addEventListener('change', createEmitCheckedPropertyUpdateFunction('collisionsWillMove'));
             elLifetime.addEventListener('change', createEmitNumberPropertyUpdateFunction('lifetime'));
@@ -616,9 +616,9 @@
         </tr>
 
         <tr>
-            <td class="label">Mass</td>
+            <td class="label">Density</td>
             <td>
-                <input type='number' id="property-mass"></input>
+                <input type='number' id="property-density"></input>
             </td>
         </tr>
 

examples/libraries/ToolTip.js

@@ -68,7 +68,7 @@ function Tooltip() {
             text += "Lifetime: " + properties.lifetime + "\n"
         }
         text += "Age: " + properties.ageAsText + "\n"
-        text += "Mass: " + properties.mass + "\n"
+        text += "Density: " + properties.density + "\n"
         text += "Script: " + properties.script + "\n"
 
 

examples/libraries/entityPropertyDialogBox.js

@@ -164,7 +164,7 @@ EntityPropertyDialogBox = (function () {
 
         array.push({ label: "Collisions:", type: "header" });
         index++;
-        array.push({ label: "Mass:", value: properties.mass.toFixed(decimals) });
+        array.push({ label: "Density:", value: properties.density.toFixed(decimals) });
         index++;
         array.push({ label: "Ignore for Collisions:", type: "checkbox", value: properties.ignoreForCollisions });
         index++;
@@ -353,7 +353,7 @@ EntityPropertyDialogBox = (function () {
             properties.gravity.z = array[index++].value;
 
             index++; // skip header
-            properties.mass = array[index++].value;
+            properties.density = array[index++].value;
             properties.ignoreForCollisions = array[index++].value;
             properties.collisionsWillMove = array[index++].value;
 

libraries/entities/src/EntityCollisionSystem.cpp

@@ -134,8 +134,8 @@ void EntityCollisionSystem::updateCollisionWithEntities(EntityItem* entityA) {
                 glm::vec3 axis = glm::normalize(penetration);
                 glm::vec3 axialVelocity = glm::dot(relativeVelocity, axis) * axis;
 
-                float massA = entityA->getMass();
+                float massA = entityA->computeMass();
-                float massB = entityB->getMass();
+                float massB = entityB->computeMass();
                 float totalMass = massA + massB;
                 float massRatioA = (2.0f * massB / totalMass);
                 float massRatioB = (2.0f * massA / totalMass);

libraries/entities/src/EntityItem.cpp

@@ -37,10 +37,10 @@ void EntityItem::initFromEntityItemID(const EntityItemID& entityItemID) {
 
     _position = ENTITY_ITEM_ZERO_VEC3;
     _dimensions = ENTITY_ITEM_DEFAULT_DIMENSIONS;
+    _density = ENTITY_ITEM_DEFAULT_DENSITY;
     _rotation = ENTITY_ITEM_DEFAULT_ROTATION;
     _glowLevel = ENTITY_ITEM_DEFAULT_GLOW_LEVEL;
     _localRenderAlpha = ENTITY_ITEM_DEFAULT_LOCAL_RENDER_ALPHA;
-    _mass = ENTITY_ITEM_DEFAULT_MASS;
     _velocity = ENTITY_ITEM_DEFAULT_VELOCITY;
     _gravity = ENTITY_ITEM_DEFAULT_GRAVITY;
     _damping = ENTITY_ITEM_DEFAULT_DAMPING;
@@ -103,7 +103,7 @@ EntityPropertyFlags EntityItem::getEntityProperties(EncodeBitstreamParams& param
     requestedProperties += PROP_POSITION;
     requestedProperties += PROP_DIMENSIONS; // NOTE: PROP_RADIUS obsolete
     requestedProperties += PROP_ROTATION;
-    requestedProperties += PROP_MASS;
+    requestedProperties += PROP_DENSITY;
     requestedProperties += PROP_VELOCITY;
     requestedProperties += PROP_GRAVITY;
     requestedProperties += PROP_DAMPING;
@@ -219,7 +219,7 @@ OctreeElement::AppendState EntityItem::appendEntityData(OctreePacketData* packet
         }
 
         APPEND_ENTITY_PROPERTY(PROP_ROTATION, appendValue, getRotation());
-        APPEND_ENTITY_PROPERTY(PROP_MASS, appendValue, getMass());
+        APPEND_ENTITY_PROPERTY(PROP_DENSITY, appendValue, getDensity());
         APPEND_ENTITY_PROPERTY(PROP_VELOCITY, appendValue, getVelocity());
         APPEND_ENTITY_PROPERTY(PROP_GRAVITY, appendValue, getGravity());
         APPEND_ENTITY_PROPERTY(PROP_DAMPING, appendValue, getDamping());
@@ -495,7 +495,7 @@ int EntityItem::readEntityDataFromBuffer(const unsigned char* data, int bytesLef
         }
                 
         READ_ENTITY_PROPERTY_QUAT_SETTER(PROP_ROTATION, updateRotation);
-        READ_ENTITY_PROPERTY_SETTER(PROP_MASS, float, updateMass);
+        READ_ENTITY_PROPERTY_SETTER(PROP_DENSITY, float, updateDensity);
         READ_ENTITY_PROPERTY_SETTER(PROP_VELOCITY, glm::vec3, updateVelocity);
         READ_ENTITY_PROPERTY_SETTER(PROP_GRAVITY, glm::vec3, updateGravity);
         READ_ENTITY_PROPERTY(PROP_DAMPING, float, _damping);
@@ -555,6 +555,44 @@ void EntityItem::adjustEditPacketForClockSkew(unsigned char* editPacketBuffer, s
     }
 }
 
+float EntityItem::computeMass() const { 
+    // NOTE: we group the operations here in and attempt to reduce floating point error.
+    return ((_density * (_volumeMultiplier * _dimensions.x)) * _dimensions.y) * _dimensions.z;
+}
+
+void EntityItem::setDensity(float density) {
+    _density = glm::max(glm::min(density, ENTITY_ITEM_MAX_DENSITY), ENTITY_ITEM_MIN_DENSITY);
+}
+
+void EntityItem::updateDensity(float density) {
+    const float MIN_DENSITY_CHANGE_FACTOR = 0.001f; // 0.1 percent
+    float newDensity = glm::max(glm::min(density, ENTITY_ITEM_MAX_DENSITY), ENTITY_ITEM_MIN_DENSITY);
+    if (fabsf(_density - newDensity) / _density > MIN_DENSITY_CHANGE_FACTOR) {
+        _density = newDensity;
+        _dirtyFlags |= EntityItem::DIRTY_MASS;
+    }
+}
+
+void EntityItem::setMass(float mass) {
+    // Setting the mass actually changes the _density (at fixed volume), however
+    // we must protect the density range to help maintain stability of physics simulation
+    // therefore this method might not accept the mass that is supplied.
+
+    // NOTE: when computing the volume we group the _volumeMultiplier (typically a very large number, due
+    // to the TREE_SCALE transformation) with the first dimension component (typically a very small number) 
+    // in an attempt to reduce floating point error of the final result.
+    float volume = (_volumeMultiplier * _dimensions.x) * _dimensions.y * _dimensions.z;
+
+    // compute new density
+    const float MIN_VOLUME = 1.0e-6f; // 0.001mm^3
+    if (volume < 1.0e-6f) {
+        // avoid divide by zero
+        _density = glm::min(mass / MIN_VOLUME, ENTITY_ITEM_MAX_DENSITY);
+    } else {
+        _density = glm::max(glm::min(mass / volume, ENTITY_ITEM_MAX_DENSITY), ENTITY_ITEM_MIN_DENSITY);
+    }
+}
+
 const float ENTITY_ITEM_EPSILON_VELOCITY_LENGTH = 0.001f / (float)TREE_SCALE;
 
 // TODO: we probably want to change this to make "down" be the direction of the entity's gravity vector
@@ -771,7 +809,7 @@ EntityItemProperties EntityItem::getProperties() const {
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(position, getPositionInMeters);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(dimensions, getDimensionsInMeters); // NOTE: radius is obsolete
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(rotation, getRotation);
-    COPY_ENTITY_PROPERTY_TO_PROPERTIES(mass, getMass);
+    COPY_ENTITY_PROPERTY_TO_PROPERTIES(density, getDensity);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(velocity, getVelocityInMeters);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(gravity, getGravityInMeters);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(damping, getDamping);
@@ -799,7 +837,7 @@ bool EntityItem::setProperties(const EntityItemProperties& properties) {
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(position, updatePositionInMeters); // this will call recalculate collision shape if needed
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(dimensions, updateDimensionsInMeters); // NOTE: radius is obsolete
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(rotation, updateRotation);
-    SET_ENTITY_PROPERTY_FROM_PROPERTIES(mass, updateMass);
+    SET_ENTITY_PROPERTY_FROM_PROPERTIES(density, updateDensity);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(velocity, updateVelocityInMeters);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(gravity, updateGravityInMeters);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(damping, updateDamping);
@@ -999,7 +1037,6 @@ void EntityItem::recalculateCollisionShape() {
 
 const float MIN_POSITION_DELTA = 0.0001f;
 const float MIN_ALIGNMENT_DOT = 0.9999f;
-const float MIN_MASS_DELTA = 0.001f;
 const float MIN_VELOCITY_DELTA = 0.01f;
 const float MIN_DAMPING_DELTA = 0.001f;
 const float MIN_GRAVITY_DELTA = 0.001f;
@@ -1047,9 +1084,29 @@ void EntityItem::updateRotation(const glm::quat& rotation) {
     }
 }
 
-void EntityItem::updateMass(float value) {
+void EntityItem::updateMass(float mass) {
-    if (fabsf(_mass - value) > MIN_MASS_DELTA) {
+    // Setting the mass actually changes the _density (at fixed volume), however
-        _mass = value;
+    // we must protect the density range to help maintain stability of physics simulation
+    // therefore this method might not accept the mass that is supplied.
+
+    // NOTE: when computing the volume we group the _volumeMultiplier (typically a very large number, due
+    // to the TREE_SCALE transformation) with the first dimension component (typically a very small number) 
+    // in an attempt to reduce floating point error of the final result.
+    float volume = (_volumeMultiplier * _dimensions.x) * _dimensions.y * _dimensions.z;
+
+    // compute new density
+    float newDensity = _density;
+    const float MIN_VOLUME = 1.0e-6f; // 0.001mm^3
+    if (volume < 1.0e-6f) {
+        // avoid divide by zero
+        newDensity = glm::min(mass / MIN_VOLUME, ENTITY_ITEM_MAX_DENSITY);
+    } else {
+        newDensity = glm::max(glm::min(mass / volume, ENTITY_ITEM_MAX_DENSITY), ENTITY_ITEM_MIN_DENSITY);
+    }
+
+    const float MIN_DENSITY_CHANGE_FACTOR = 0.001f; // 0.1 percent
+    if (fabsf(_density - newDensity) / _density > MIN_DENSITY_CHANGE_FACTOR) {
+        _density = newDensity;
         _dirtyFlags |= EntityItem::DIRTY_MASS;
     }
 }

libraries/entities/src/EntityItem.h

@@ -171,8 +171,11 @@ public:
     float getLocalRenderAlpha() const { return _localRenderAlpha; }
     void setLocalRenderAlpha(float localRenderAlpha) { _localRenderAlpha = localRenderAlpha; }
 
-    float getMass() const { return _mass; }
+    void setDensity(float density);
-    void setMass(float value) { _mass = value; }
+    float computeMass() const;
+    void setMass(float mass);
+
+    float getDensity() const { return _density; }
 
     const glm::vec3& getVelocity() const { return _velocity; } /// velocity in domain scale units (0.0-1.0) per second
     glm::vec3 getVelocityInMeters() const { return _velocity * (float) TREE_SCALE; } /// get velocity in meters
@@ -260,6 +263,7 @@ public:
     void updateDimensions(const glm::vec3& value);
     void updateDimensionsInMeters(const glm::vec3& value);
     void updateRotation(const glm::quat& rotation);
+    void updateDensity(float value);
     void updateMass(float value);
     void updateVelocity(const glm::vec3& value);
     void updateVelocityInMeters(const glm::vec3& value);
@@ -303,7 +307,12 @@ protected:
     glm::quat _rotation;
     float _glowLevel;
     float _localRenderAlpha;
-    float _mass;
+    float _density = ENTITY_ITEM_DEFAULT_DENSITY; // kg/m^3
+    // NOTE: _volumeMultiplier is used to compute volume:
+    // volume = _volumeMultiplier * _dimensions.x * _dimensions.y * _dimensions.z  =  m^3
+    // DANGER: due to the size of TREE_SCALE the _volumeMultiplier is always a large number, and therefore 
+    // will tend to introduce floating point error.  We must keep this in mind when using it.
+    float _volumeMultiplier = (float)TREE_SCALE * (float)TREE_SCALE * (float)TREE_SCALE;
     glm::vec3 _velocity;
     glm::vec3 _gravity;
     float _damping;

libraries/entities/src/EntityItemProperties.cpp

@@ -30,7 +30,7 @@ EntityItemProperties::EntityItemProperties() :
     CONSTRUCT_PROPERTY(position, 0),
     CONSTRUCT_PROPERTY(dimensions, ENTITY_ITEM_DEFAULT_DIMENSIONS),
     CONSTRUCT_PROPERTY(rotation, ENTITY_ITEM_DEFAULT_ROTATION),
-    CONSTRUCT_PROPERTY(mass, ENTITY_ITEM_DEFAULT_MASS),
+    CONSTRUCT_PROPERTY(density, ENTITY_ITEM_DEFAULT_DENSITY),
     CONSTRUCT_PROPERTY(velocity, ENTITY_ITEM_DEFAULT_VELOCITY),
     CONSTRUCT_PROPERTY(gravity, ENTITY_ITEM_DEFAULT_GRAVITY),
     CONSTRUCT_PROPERTY(damping, ENTITY_ITEM_DEFAULT_DAMPING),
@@ -175,7 +175,7 @@ EntityPropertyFlags EntityItemProperties::getChangedProperties() const {
     CHECK_PROPERTY_CHANGE(PROP_DIMENSIONS, dimensions);
     CHECK_PROPERTY_CHANGE(PROP_POSITION, position);
     CHECK_PROPERTY_CHANGE(PROP_ROTATION, rotation);
-    CHECK_PROPERTY_CHANGE(PROP_MASS, mass);
+    CHECK_PROPERTY_CHANGE(PROP_DENSITY, density);
     CHECK_PROPERTY_CHANGE(PROP_VELOCITY, velocity);
     CHECK_PROPERTY_CHANGE(PROP_GRAVITY, gravity);
     CHECK_PROPERTY_CHANGE(PROP_DAMPING, damping);
@@ -232,7 +232,7 @@ QScriptValue EntityItemProperties::copyToScriptValue(QScriptEngine* engine) cons
     COPY_PROPERTY_TO_QSCRIPTVALUE_VEC3(velocity);
     COPY_PROPERTY_TO_QSCRIPTVALUE_VEC3(gravity);
     COPY_PROPERTY_TO_QSCRIPTVALUE(damping);
-    COPY_PROPERTY_TO_QSCRIPTVALUE(mass);
+    COPY_PROPERTY_TO_QSCRIPTVALUE(density);
     COPY_PROPERTY_TO_QSCRIPTVALUE(lifetime);
     COPY_PROPERTY_TO_QSCRIPTVALUE_GETTER(age, getAge()); // gettable, but not settable
     COPY_PROPERTY_TO_QSCRIPTVALUE_GETTER(ageAsText, formatSecondsElapsed(getAge())); // gettable, but not settable
@@ -310,7 +310,7 @@ void EntityItemProperties::copyFromScriptValue(const QScriptValue& object) {
     COPY_PROPERTY_FROM_QSCRIPTVALUE_VEC3(position, setPosition);
     COPY_PROPERTY_FROM_QSCRIPTVALUE_VEC3(dimensions, setDimensions);
     COPY_PROPERTY_FROM_QSCRIPTVALUE_QUAT(rotation, setRotation);
-    COPY_PROPERTY_FROM_QSCRIPTVALUE_FLOAT(mass, setMass);
+    COPY_PROPERTY_FROM_QSCRIPTVALUE_FLOAT(density, setDensity);
     COPY_PROPERTY_FROM_QSCRIPTVALUE_VEC3(velocity, setVelocity);
     COPY_PROPERTY_FROM_QSCRIPTVALUE_VEC3(gravity, setGravity);
     COPY_PROPERTY_FROM_QSCRIPTVALUE_FLOAT(damping, setDamping);
@@ -479,7 +479,7 @@ bool EntityItemProperties::encodeEntityEditPacket(PacketType command, EntityItem
             APPEND_ENTITY_PROPERTY(PROP_POSITION, appendPosition, properties.getPosition());
             APPEND_ENTITY_PROPERTY(PROP_DIMENSIONS, appendValue, properties.getDimensions()); // NOTE: PROP_RADIUS obsolete
             APPEND_ENTITY_PROPERTY(PROP_ROTATION, appendValue, properties.getRotation());
-            APPEND_ENTITY_PROPERTY(PROP_MASS, appendValue, properties.getMass());
+            APPEND_ENTITY_PROPERTY(PROP_DENSITY, appendValue, properties.getDensity());
             APPEND_ENTITY_PROPERTY(PROP_VELOCITY, appendValue, properties.getVelocity());
             APPEND_ENTITY_PROPERTY(PROP_GRAVITY, appendValue, properties.getGravity());
             APPEND_ENTITY_PROPERTY(PROP_DAMPING, appendValue, properties.getDamping());
@@ -700,7 +700,7 @@ bool EntityItemProperties::decodeEntityEditPacket(const unsigned char* data, int
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_POSITION, glm::vec3, setPosition);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_DIMENSIONS, glm::vec3, setDimensions);  // NOTE: PROP_RADIUS obsolete
     READ_ENTITY_PROPERTY_QUAT_TO_PROPERTIES(PROP_ROTATION, setRotation);
-    READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_MASS, float, setMass);
+    READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_DENSITY, float, setDensity);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_VELOCITY, glm::vec3, setVelocity);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_GRAVITY, glm::vec3, setGravity);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_DAMPING, float, setDamping);
@@ -781,7 +781,7 @@ void EntityItemProperties::markAllChanged() {
     _positionChanged = true;
     _dimensionsChanged = true;
     _rotationChanged = true;
-    _massChanged = true;
+    _densityChanged = true;
     _velocityChanged = true;
     _gravityChanged = true;
     _dampingChanged = true;

libraries/entities/src/EntityItemProperties.h

@@ -42,7 +42,7 @@ enum EntityPropertyList {
     PROP_RADIUS, // NOTE: PROP_RADIUS is obsolete and only included in old format streams
     PROP_DIMENSIONS = PROP_RADIUS,
     PROP_ROTATION,
-    PROP_MASS,
+    PROP_DENSITY,
     PROP_VELOCITY,
     PROP_GRAVITY,
     PROP_DAMPING,
@@ -145,7 +145,7 @@ public:
     DEFINE_PROPERTY_REF_WITH_SETTER(PROP_POSITION, Position, position, glm::vec3);
     DEFINE_PROPERTY_REF(PROP_DIMENSIONS, Dimensions, dimensions, glm::vec3);
     DEFINE_PROPERTY_REF(PROP_ROTATION, Rotation, rotation, glm::quat);
-    DEFINE_PROPERTY(PROP_MASS, Mass, mass, float);
+    DEFINE_PROPERTY(PROP_DENSITY, Density, density, float);
     DEFINE_PROPERTY_REF(PROP_VELOCITY, Velocity, velocity, glm::vec3);
     DEFINE_PROPERTY_REF(PROP_GRAVITY, Gravity, gravity, glm::vec3);
     DEFINE_PROPERTY(PROP_DAMPING, Damping, damping, float);

libraries/entities/src/EntityItemPropertiesDefaults.h

@@ -36,8 +36,14 @@ const float ENTITY_ITEM_IMMORTAL_LIFETIME = -1.0f; /// special lifetime which me
 const float ENTITY_ITEM_DEFAULT_LIFETIME = ENTITY_ITEM_IMMORTAL_LIFETIME;
 
 const glm::quat ENTITY_ITEM_DEFAULT_ROTATION;
-const glm::vec3 ENTITY_ITEM_DEFAULT_DIMENSIONS = glm::vec3(0.1f) / (float)TREE_SCALE;
+const float ENTITY_ITEM_DEFAULT_WIDTH = 0.1f;
-const float ENTITY_ITEM_DEFAULT_MASS = 1.0f;
+const glm::vec3 ENTITY_ITEM_DEFAULT_DIMENSIONS = glm::vec3(ENTITY_ITEM_DEFAULT_WIDTH) / (float)TREE_SCALE;
+const float ENTITY_ITEM_DEFAULT_VOLUME = ENTITY_ITEM_DEFAULT_WIDTH * ENTITY_ITEM_DEFAULT_WIDTH * ENTITY_ITEM_DEFAULT_WIDTH;
+
+const float ENTITY_ITEM_MAX_DENSITY = 10000.0f; // kg/m^3 density of silver
+const float ENTITY_ITEM_MIN_DENSITY = 100.0f; // kg/m^3 density of balsa wood
+const float ENTITY_ITEM_DEFAULT_DENSITY = 1000.0f;   // density of water
+const float ENTITY_ITEM_DEFAULT_MASS = ENTITY_ITEM_DEFAULT_DENSITY * ENTITY_ITEM_DEFAULT_VOLUME;
 
 const glm::vec3 ENTITY_ITEM_DEFAULT_VELOCITY = ENTITY_ITEM_ZERO_VEC3;
 const glm::vec3 ENTITY_ITEM_DEFAULT_ANGULAR_VELOCITY = ENTITY_ITEM_ZERO_VEC3;

libraries/entities/src/SphereEntityItem.cpp

@@ -32,6 +32,10 @@ SphereEntityItem::SphereEntityItem(const EntityItemID& entityItemID, const Entit
 { 
     _type = EntityTypes::Sphere;
     setProperties(properties);
+    // NOTE: _volumeMultiplier is used to compute volume:
+    // volume = _volumeMultiplier * _dimensions.x * _dimensions.y * _dimensions.z
+    // The formula below looks funny because _dimension.xyz = diameter rather than radius.
+    _volumeMultiplier *= PI / 6.0f;
 }
 
 EntityItemProperties SphereEntityItem::getProperties() const {

libraries/physics/src/EntityMotionState.cpp

@@ -109,7 +109,7 @@ void EntityMotionState::updateObjectEasy(uint32_t flags, uint32_t frame) {
     _body->setDamping(_linearDamping, _angularDamping);
 
     if (flags & EntityItem::DIRTY_MASS) {
-        float mass = getMass();
+        float mass = _entity->computeMass();
         btVector3 inertia(0.0f, 0.0f, 0.0f);
         _body->getCollisionShape()->calculateLocalInertia(mass, inertia);
         _body->setMassProps(mass, inertia);
@@ -137,8 +137,12 @@ void EntityMotionState::updateObjectVelocities() {
 #endif // USE_BULLET_PHYSICS
 }
 
-void EntityMotionState::computeShapeInfo(ShapeInfo& info) {
+void EntityMotionState::computeShapeInfo(ShapeInfo& shapeInfo) {
-    _entity->computeShapeInfo(info);
+    _entity->computeShapeInfo(shapeInfo);
+}
+
+float EntityMotionState::computeMass(const ShapeInfo& shapeInfo) const {
+    return _entity->computeMass();
 }
 
 void EntityMotionState::sendUpdate(OctreeEditPacketSender* packetSender, uint32_t frame) {

libraries/physics/src/EntityMotionState.h

@@ -57,7 +57,8 @@ public:
     void updateObjectEasy(uint32_t flags, uint32_t frame);
     void updateObjectVelocities();
 
-    void computeShapeInfo(ShapeInfo& info);
+    void computeShapeInfo(ShapeInfo& shapeInfo);
+    float computeMass(const ShapeInfo& shapeInfo) const;
 
     void sendUpdate(OctreeEditPacketSender* packetSender, uint32_t frame);
 

libraries/physics/src/ObjectMotionState.cpp

@@ -44,13 +44,10 @@ const glm::vec3& ObjectMotionState::getWorldOffset() {
 
 
 ObjectMotionState::ObjectMotionState() : 
-    _density(DEFAULT_DENSITY), 
-    _volume(DEFAULT_VOLUME), 
     _friction(DEFAULT_FRICTION), 
     _restitution(DEFAULT_RESTITUTION), 
     _linearDamping(0.0f),
     _angularDamping(0.0f),
-    _wasInWorld(false),
     _motionType(MOTION_TYPE_STATIC),
     _body(NULL),
     _sentMoving(false),
@@ -69,10 +66,6 @@ ObjectMotionState::~ObjectMotionState() {
     assert(_body == NULL);
 }
 
-void ObjectMotionState::setDensity(float density) {
-    _density = btMax(btMin(fabsf(density), MAX_DENSITY), MIN_DENSITY);
-}
-
 void ObjectMotionState::setFriction(float friction) {
     _friction = btMax(btMin(fabsf(friction), MAX_FRICTION), 0.0f);
 }
@@ -89,10 +82,6 @@ void ObjectMotionState::setAngularDamping(float damping) {
     _angularDamping = btMax(btMin(fabsf(damping), 1.0f), 0.0f);
 }
 
-void ObjectMotionState::setVolume(float volume) {
-    _volume = btMax(btMin(fabsf(volume), MAX_VOLUME), MIN_VOLUME);
-}
-
 void ObjectMotionState::setVelocity(const glm::vec3& velocity) const {
     _body->setLinearVelocity(glmToBullet(velocity));
 }

libraries/physics/src/ObjectMotionState.h

@@ -60,18 +60,15 @@ public:
     virtual void updateObjectEasy(uint32_t flags, uint32_t frame) = 0;
     virtual void updateObjectVelocities() = 0;
 
-    virtual void computeShapeInfo(ShapeInfo& info) = 0;
-
     virtual MotionType getMotionType() const { return _motionType; }
 
-    void setDensity(float density);
+    virtual void computeShapeInfo(ShapeInfo& info) = 0;
+    virtual float computeMass(const ShapeInfo& shapeInfo) const = 0;
+
     void setFriction(float friction);
     void setRestitution(float restitution);
     void setLinearDamping(float damping);
     void setAngularDamping(float damping);
-    void setVolume(float volume);
-
-    float getMass() const { return _volume * _density; }
 
     void setVelocity(const glm::vec3& velocity) const;
     void setAngularVelocity(const glm::vec3& velocity) const;
@@ -92,13 +89,12 @@ public:
 
     friend class PhysicsEngine;
 protected:
-    float _density;
+    // TODO: move these materials properties to EntityItem
-    float _volume;
     float _friction;
     float _restitution;
     float _linearDamping;
     float _angularDamping;
-    bool _wasInWorld;
+
     MotionType _motionType;
 
     // _body has NO setters -- it is only changed by PhysicsEngine

libraries/physics/src/PhysicsEngine.cpp

@@ -246,9 +246,9 @@ void PhysicsEngine::stepSimulation() {
 
 bool PhysicsEngine::addObject(ObjectMotionState* motionState) {
     assert(motionState);
-    ShapeInfo info;
+    ShapeInfo shapeInfo;
-    motionState->computeShapeInfo(info);
+    motionState->computeShapeInfo(shapeInfo);
-    btCollisionShape* shape = _shapeManager.getShape(info);
+    btCollisionShape* shape = _shapeManager.getShape(shapeInfo);
     if (shape) {
         btVector3 inertia(0.0f, 0.0f, 0.0f);
         float mass = 0.0f;
@@ -263,7 +263,7 @@ bool PhysicsEngine::addObject(ObjectMotionState* motionState) {
                 break;
             }
             case MOTION_TYPE_DYNAMIC: {
-                mass = motionState->getMass();
+                mass = motionState->computeMass(shapeInfo);
                 shape->calculateLocalInertia(mass, inertia);
                 body = new btRigidBody(mass, motionState, shape, inertia);
                 body->updateInertiaTensor();
@@ -301,10 +301,10 @@ bool PhysicsEngine::removeObject(ObjectMotionState* motionState) {
     btRigidBody* body = motionState->_body;
     if (body) {
         const btCollisionShape* shape = body->getCollisionShape();
-        ShapeInfo info;
+        ShapeInfo shapeInfo;
-        ShapeInfoUtil::collectInfoFromShape(shape, info);
+        ShapeInfoUtil::collectInfoFromShape(shape, shapeInfo);
         _dynamicsWorld->removeRigidBody(body);
-        _shapeManager.releaseShape(info);
+        _shapeManager.releaseShape(shapeInfo);
         delete body;
         motionState->_body = NULL;
         return true;
@@ -320,20 +320,31 @@ void PhysicsEngine::updateObjectHard(btRigidBody* body, ObjectMotionState* motio
     _dynamicsWorld->removeRigidBody(body);
 
     if (flags & EntityItem::DIRTY_SHAPE) {
+        // MASS bit should be set whenever SHAPE is set
+        assert(flags & EntityItem::DIRTY_MASS);
+
+        // get new shape
         btCollisionShape* oldShape = body->getCollisionShape();
-        ShapeInfo info;
+        ShapeInfo shapeInfo;
-        motionState->computeShapeInfo(info);
+        motionState->computeShapeInfo(shapeInfo);
-        btCollisionShape* newShape = _shapeManager.getShape(info);
+        btCollisionShape* newShape = _shapeManager.getShape(shapeInfo);
         if (newShape != oldShape) {
+            // BUG: if shape doesn't change but density does then we won't compute new mass properties
+            // TODO: fix this BUG by replacing DIRTY_MASS with DIRTY_DENSITY and then fix logic accordingly.
             body->setCollisionShape(newShape);
             _shapeManager.releaseShape(oldShape);
+
+            // compute mass properties
+            float mass = motionState->computeMass(shapeInfo);
+            btVector3 inertia(0.0f, 0.0f, 0.0f);
+            body->getCollisionShape()->calculateLocalInertia(mass, inertia);
+            body->setMassProps(mass, inertia);
+            body->updateInertiaTensor();
         } else {
             // whoops, shape hasn't changed after all so we must release the reference
             // that was created when looking it up
             _shapeManager.releaseShape(newShape);
         }
-        // MASS bit should be set whenever SHAPE is set
-        assert(flags & EntityItem::DIRTY_MASS);
     }
     bool easyUpdate = flags & EASY_DIRTY_PHYSICS_FLAGS;
     if (easyUpdate) {
@@ -356,9 +367,11 @@ void PhysicsEngine::updateObjectHard(btRigidBody* body, ObjectMotionState* motio
             int collisionFlags = body->getCollisionFlags() & ~(btCollisionObject::CF_KINEMATIC_OBJECT | btCollisionObject::CF_STATIC_OBJECT);
             body->setCollisionFlags(collisionFlags);
             if (! (flags & EntityItem::DIRTY_MASS)) {
-                // always update mass properties when going dynamic (unless it's already been done)
+                // always update mass properties when going dynamic (unless it's already been done above)
+                ShapeInfo shapeInfo;
+                motionState->computeShapeInfo(shapeInfo);
+                float mass = motionState->computeMass(shapeInfo);
                 btVector3 inertia(0.0f, 0.0f, 0.0f);
-                float mass = motionState->getMass();
                 body->getCollisionShape()->calculateLocalInertia(mass, inertia);
                 body->setMassProps(mass, inertia);
                 body->updateInertiaTensor();

libraries/shared/src/ShapeInfo.cpp

@@ -24,18 +24,21 @@ void ShapeInfo::clear() {
 void ShapeInfo::setBox(const glm::vec3& halfExtents) {
     _type = BOX_SHAPE;
     _data.clear();
+    // _data[0] = < halfX, halfY, halfZ >
     _data.push_back(halfExtents);
 }
 
 void ShapeInfo::setSphere(float radius) {
     _type = SPHERE_SHAPE;
     _data.clear();
+    // _data[0] = < radius, radius, radius >
     _data.push_back(glm::vec3(radius));
 }
 
 void ShapeInfo::setCylinder(float radius, float halfHeight) {
     _type = CYLINDER_SHAPE;
     _data.clear();
+    // _data[0] = < radius, halfHeight, radius >
     // NOTE: default cylinder has (UpAxis = 1) axis along yAxis and radius stored in X
     _data.push_back(glm::vec3(radius, halfHeight, radius));
 }
@@ -43,6 +46,7 @@ void ShapeInfo::setCylinder(float radius, float halfHeight) {
 void ShapeInfo::setCapsule(float radius, float halfHeight) {
     _type = CAPSULE_SHAPE;
     _data.clear();
+    // _data[0] = < radius, halfHeight, radius >
     _data.push_back(glm::vec3(radius, halfHeight, radius));
 }
 
@@ -58,3 +62,34 @@ glm::vec3 ShapeInfo::getBoundingBoxDiagonal() const {
     }
     return glm::vec3(0.0f);
 }
+
+float ShapeInfo::computeVolume() const {
+    const float DEFAULT_VOLUME = 1.0f;
+    float volume = DEFAULT_VOLUME;
+    switch(_type) {
+        case BOX_SHAPE: {
+            // factor of 8.0 because the components of _data[0] are all halfExtents
+            volume = 8.0f * _data[0].x * _data[0].y * _data[0].z;
+            break;
+        }
+        case SPHERE_SHAPE: {
+            float radius = _data[0].x;
+            volume = 4.0f * PI * radius * radius * radius / 3.0f;
+            break;
+        }
+        case CYLINDER_SHAPE: {
+            float radius = _data[0].x;
+            volume = PI * radius * radius * 2.0f * _data[0].y;
+            break;
+        }
+        case CAPSULE_SHAPE: {
+            float radius = _data[0].x;
+            volume = PI * radius * radius * (2.0f * _data[0].y + 4.0f * radius / 3.0f);
+            break;
+        }
+        default:
+            break;
+    }
+    assert(volume > 0.0f);
+    return volume;
+}

libraries/shared/src/ShapeInfo.h

@@ -32,6 +32,7 @@ public:
     const QVector<glm::vec3>& getData() const { return _data; }
 
     glm::vec3 getBoundingBoxDiagonal() const;
+    float computeVolume() const;
 
 protected:
     int _type;