Improve avatar movement, added Physics.cpp for routines to help with physics calculations

interface/src/Avatar.cpp

@@ -16,12 +16,14 @@
 #include "Hand.h"
 #include "Head.h"
 #include "Log.h"
+#include "Physics.h"
 #include "ui/TextRenderer.h"
 #include <NodeList.h>
 #include <NodeTypes.h>
 #include <PacketHeaders.h>
 #include <OculusManager.h>
 
+
 using namespace std;
 
 const bool  BALLS_ON                      = false;
@@ -553,21 +555,13 @@ void Avatar::simulate(float deltaTime, Transmitter* transmitter) {
         _bodyYawDelta   *= bodySpinMomentum;
         _bodyRollDelta  *= bodySpinMomentum;
         
-        // Decay velocity.  If velocity is really low, increase decay to simulate static friction
-        const float VELOCITY_DECAY_UNDER_THRUST = 0.2;
-        const float VELOCITY_FAST_DECAY = 0.6;
-        const float VELOCITY_SLOW_DECAY = 3.0;
-        const float VELOCITY_FAST_THRESHOLD = 2.0f;
-        float decayConstant, decay;
-        if (glm::length(_thrust) > 0.f) {
-            decayConstant = VELOCITY_DECAY_UNDER_THRUST;
-        } else if (glm::length(_velocity) > VELOCITY_FAST_THRESHOLD) {
-            decayConstant = VELOCITY_FAST_DECAY;
-        } else {
-            decayConstant = VELOCITY_SLOW_DECAY;
-        }             
-        decay = glm::clamp(1.0f - decayConstant * deltaTime, 0.0f, 1.0f);
-        _velocity *= decay;
+        const float MAX_STATIC_FRICTION_VELOCITY = 0.25f;
+        const float STATIC_FRICTION_STRENGTH = 20.f;
+        applyStaticFriction(deltaTime, _velocity, MAX_STATIC_FRICTION_VELOCITY, STATIC_FRICTION_STRENGTH);
+        
+        const float LINEAR_DAMPING_STRENGTH = 0.2f;
+        const float SQUARED_DAMPING_STRENGTH = 0.1f;
+        applyDamping(deltaTime, _velocity, LINEAR_DAMPING_STRENGTH, SQUARED_DAMPING_STRENGTH);
                 
         //pitch and roll the body as a function of forward speed and turning delta
         const float BODY_PITCH_WHILE_WALKING      = -20.0;

interface/src/Physics.cpp

@@ -0,0 +1,40 @@
+//
+//  Physics.cpp
+//  hifi
+//
+//  Created by Philip on July 11, 2013
+//
+//  Routines to help with doing virtual world physics
+//
+
+#include <glm/glm.hpp>
+#include <SharedUtil.h>
+
+#include "Util.h"
+#include "world.h"
+#include "Physics.h"
+
+//
+//  Applies static friction:  maxVelocity is the largest velocity for which there
+//  there is friction, and strength is the amount of friction force applied to reduce
+//  velocity. 
+// 
+void applyStaticFriction(float deltaTime, glm::vec3& velocity, float maxVelocity, float strength) {
+    float v = glm::length(velocity);
+    if (v < maxVelocity) {
+        velocity *= glm::clamp((1.0f - deltaTime * strength * (1.f - v / maxVelocity)), 0.0f, 1.0f);
+    }
+}
+
+//
+//  Applies velocity damping, with a strength value for linear and squared velocity damping
+//
+
+void applyDamping(float deltaTime, glm::vec3& velocity, float linearStrength, float squaredStrength) {
+    if (squaredStrength == 0.f) {
+        velocity *= glm::clamp(1.f - deltaTime * linearStrength, 0.f, 1.f);
+    } else {
+        velocity *= glm::clamp(1.f - deltaTime * (linearStrength + glm::length(velocity) * squaredStrength), 0.f, 1.f);
+    }
+}
+

interface/src/Physics.h

@@ -0,0 +1,15 @@
+//
+//  Balls.h
+//  hifi
+//
+//  Created by Philip on 4/25/13.
+//
+//
+
+#ifndef hifi_Physics_h
+#define hifi_Physics_h
+
+void applyStaticFriction(float deltaTime, glm::vec3& velocity, float maxVelocity, float strength);
+void applyDamping(float deltaTime, glm::vec3& velocity, float linearStrength, float squaredStrength);
+
+#endif