Started experimenting with Bullet

git-svn-id: https://openmw.svn.sourceforge.net/svnroot/openmw/trunk@46 ea6a568a-9f4f-0410-981a-c910a81bb256

Makefile

@@ -8,14 +8,18 @@ DMD=gdmd -version=Posix
 # Some extra flags for niftool and bsatool
 NIFFLAGS=-debug=warnstd -debug=check -debug=statecheck -debug=strict -debug=verbose
 
-# Compiler settings for Ogre + OIS. Change as needed.
+# Compiler settings for Ogre + OIS.
 CF_OIS=$(shell pkg-config --cflags OGRE OIS)
 OGCC=$(CXX) $(CXXFLAGS) $(CF_OIS)
 
-# Compiler settings for ffmpeg. Change as needed.
+# Compiler settings for ffmpeg.
 CF_FFMPEG=$(shell pkg-config --cflags libavcodec libavformat)
 AVGCC=$(CXX) $(CXXFLAGS) $(CF_FFMPEG)
 
+# Settings for Bullet
+CF_BULLET=-Iinclude/bullet
+BGCC=$(CXX) $(CXXFLAGS) $(CF_BULLET)
+
 # Ogre C++ files, on the form ogre/cpp_X.cpp. Only the first file is
 # passed to the compiler, the rest are dependencies.
 ogre_cpp=ogre framelistener interface overlay bsaarchive
@@ -23,10 +27,14 @@ ogre_cpp=ogre framelistener interface overlay bsaarchive
 # FFmpeg files, in the form sound/cpp_X.cpp.
 avcodec_cpp=avcodec
 
-## No modifications should be required below this line. ##
+# Bullet cpp files
+bullet_cpp=bullet
+
+#### No modifications should be required below this line. ####
 
 ogre_cpp_files=$(ogre_cpp:%=ogre/cpp_%.cpp)
 avcodec_cpp_files=$(avcodec_cpp:%=sound/cpp_%.cpp)
+bullet_cpp_files=$(bullet_cpp:%=bullet/cpp_%.cpp)
 
 # All object files needed by openmw and esmtool
 src := $(wildcard */*.d)
@@ -47,7 +55,7 @@ obj_nif := $(src_nif:%.d=nifobjs/%.o)
 all: openmw esmtool niftool bsatool bored
 
 # Only build C++ sources. Used when building from DSSS.
-cpp: cpp_ogre.o cpp_avcodec.o
+cpp: cpp_ogre.o cpp_avcodec.o cpp_bullet.o
 
 cpp_ogre.o: $(ogre_cpp_files)
 	$(OGCC) -c $<
@@ -55,6 +63,9 @@ cpp_ogre.o: $(ogre_cpp_files)
 cpp_avcodec.o: $(avcodec_cpp_files)
 	$(AVGCC) -c $<
 
+cpp_bullet.o: $(bullet_cpp_files)
+	$(BGCC) -c $<
+
 objs/%.o: %.d
 	dirname $@ | xargs mkdir -p
 	$(DMD) -c $< -of$@
@@ -63,8 +74,8 @@ nifobjs/%.o: %.d
 	dirname $@ | xargs mkdir -p
 	$(DMD) $(NIFFLAGS) -c $< -of$@
 
-openmw: openmw.d cpp_ogre.o cpp_avcodec.o $(obj)
+openmw: openmw.d cpp_ogre.o cpp_avcodec.o cpp_bullet.o $(obj)
-	$(DMD) $^ -of$@ -L-lopenal -L-lOgreMain -L-lOIS -L-lavcodec -L-lavformat
+	$(DMD) $^ -of$@ -L-lopenal -L-lOgreMain -L-lOIS -L-lavcodec -L-lavformat bullet/libBulletDynamics.a bullet/libBulletCollision.a bullet/libLinearMath.a
 
 esmtool: esmtool.d cpp_ogre.o cpp_avcodec.o $(obj)
 	$(DMD) $^ -of$@ -L-lopenal -L-lOgreMain -L-lOIS -L-lavcodec -L-lavformat

bullet/bindings.d

@@ -0,0 +1,43 @@
+/*
+  OpenMW - The completely unofficial reimplementation of Morrowind
+  Copyright (C) 2008  Nicolay Korslund
+  Email: < korslund@gmail.com >
+  WWW: http://openmw.snaptoad.com/
+
+  This file (bindings.d) is part of the OpenMW package.
+
+  OpenMW is distributed as free software: you can redistribute it
+  and/or modify it under the terms of the GNU General Public License
+  version 3, as published by the Free Software Foundation.
+
+  This program is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  version 3 along with this program. If not, see
+  http://www.gnu.org/licenses/ .
+
+ */
+
+module bullet.bindings;
+
+/*
+ * This module is the interface between D and the C++ code that
+ * handles Bullet.
+ */
+
+extern(C):
+
+// Initialize the dynamic world. Returns non-zero if an error occurs.
+int cpp_initBullet();
+void cpp_timeStep(float delta);
+void cpp_cleanupBullet();
+
+// Insert a debug collision object
+void cpp_insertBox(float x, float y, float z);
+
+// Move the player's collision shape
+int cpp_movePlayerCollision(float x, float y, float z,
+                            float dx, float dy, float dz);

bullet/bullet.d

@@ -0,0 +1,11 @@
+module bullet.bullet;
+
+import bullet.bindings;
+
+void initBullet()
+{
+  if(cpp_initBullet())
+    throw new Exception("Bullet setup failed");
+}
+
+void cleanupBullet() { cpp_cleanupBullet(); }

bullet/cpp_bullet.cpp

@@ -0,0 +1,196 @@
+#include "btBulletCollisionCommon.h"
+
+#include <iostream>
+
+using namespace std;
+
+btDefaultCollisionConfiguration* m_collisionConfiguration;
+btCollisionDispatcher *m_dispatcher;
+btBroadphaseInterface *m_broadphase;
+//btSequentialImpulseConstraintSolver* m_solver;
+//btDynamicsWorld *m_dynamicsWorld;
+btCollisionWorld *m_collisionWorld;
+
+//btCollisionObject* m_playerObject;
+btConvexShape *playerShape;
+
+extern "C" int32_t cpp_initBullet()
+{
+  // Set up basic objects
+  m_collisionConfiguration = new btDefaultCollisionConfiguration();
+  m_dispatcher = new btCollisionDispatcher(m_collisionConfiguration);
+  m_broadphase = new btDbvtBroadphase();
+  m_collisionWorld =
+    new btCollisionWorld(m_dispatcher, m_broadphase,
+                         m_collisionConfiguration);
+
+  /*m_solver = new btSequentialImpulseConstraintSolver;
+  m_dynamicsWorld =
+    new btDiscreteDynamicsWorld(m_dispatcher, m_broadphase,
+                                m_solver, m_collisionConfiguration);
+  m_dynamicsWorld->setGravity(btVector3(0,-10,0));
+  */
+
+  // Create player collision object
+  //playerShape = new btCylinderShape(btVector3(50, 50, 50));
+  playerShape = new btSphereShape(50);
+
+  /*
+  m_playerObject = new btCollisionObject ();
+  m_playerObject->setCollisionShape (m_shape);
+  m_playerObject->setCollisionFlags (btCollisionObject::CF_NO_CONTACT_RESPONSE);
+  */
+
+  /*
+  // Dynamic shapes:
+
+  // Re-using the same collision is better for memory usage and
+  // performance.
+
+  btCollisionShape* colShape = new btBoxShape(btVector3(1,1,1));
+  //btCollisionShape* colShape = new btSphereShape(btScalar(1.));
+  //m_collisionShapes.push_back(colShape);
+
+  // Create Dynamic Objects
+  btTransform startTransform;
+  startTransform.setIdentity();
+
+  mass = 1.f;
+
+  colShape->calculateLocalInertia(mass,localInertia);
+
+///create 125 (5x5x5) dynamic objects
+#define ARRAY_SIZE_X 5
+#define ARRAY_SIZE_Y 5
+#define ARRAY_SIZE_Z 5
+
+#define START_POS_X -5
+#define START_POS_Y -5
+#define START_POS_Z -3
+
+  float start_x = START_POS_X - ARRAY_SIZE_X/2;
+  float start_y = START_POS_Y;
+  float start_z = START_POS_Z - ARRAY_SIZE_Z/2;
+
+  for (int k=0;k<ARRAY_SIZE_Y;k++)
+    for (int i=0;i<ARRAY_SIZE_X;i++)
+      for(int j = 0;j<ARRAY_SIZE_Z;j++)
+        {
+          startTransform.setOrigin(btVector3(2.0*i + start_x,
+                                             10+2.0*k + start_y,
+                                             2.0*j + start_z));
+
+          btDefaultMotionState* myMotionState =
+            new btDefaultMotionState(startTransform);
+
+          btRigidBody::btRigidBodyConstructionInfo
+            rbInfo(mass,myMotionState,colShape,localInertia);
+
+          btRigidBody* body = new btRigidBody(rbInfo);
+          body->setActivationState(ISLAND_SLEEPING);
+
+          m_dynamicsWorld->addRigidBody(body);
+          body->setActivationState(ISLAND_SLEEPING);
+        }
+  */
+  return 0;
+}
+
+extern "C" int32_t cpp_movePlayerCollision(float x, float y, float z,
+                                        float dx, float dy, float dz)
+{
+  btTransform start, end;
+  start.setIdentity();
+  end.setIdentity();
+
+  // The sweep test moves the shape from the old position to the
+  // new. The 0.1 offset in one of the coordinates is to make sure a
+  // sweep is performed even when the player does not move.
+  start.setOrigin(btVector3(x, y, z));
+  end.setOrigin(btVector3(x+dx,y+dy,z+dz));
+
+  btCollisionWorld::ClosestConvexResultCallback cb(btVector3(0,0,0),
+                                            btVector3(0,0,0));
+
+  m_collisionWorld->convexSweepTest(playerShape, start, end, cb);
+
+  if(cb.hasHit()) return 1;
+  else return 0;
+}
+
+extern "C" void cpp_insertBox(float x, float y, float z)
+{
+  btCollisionShape* groundShape =
+    new btSphereShape(50);
+    //new btBoxShape(btVector3(100,100,100));
+
+  btTransform groundTransform;
+  groundTransform.setIdentity();
+  groundTransform.setOrigin(btVector3(x,y,z));
+
+  btCollisionObject *obj = new btCollisionObject;
+  obj->setCollisionShape(groundShape);
+  obj->setWorldTransform(groundTransform);
+
+  m_collisionWorld->addCollisionObject(obj);
+
+  /*
+  m_collisionWorld->addCollisionObject(obj,
+      btBroadphaseProxy::DebrisFilter,  // ??
+      btBroadphaseProxy::StaticFilter); // Only static objects
+
+  /*
+  btDefaultMotionState* myMotionState =
+    new btDefaultMotionState(groundTransform);
+
+  btRigidBody::btRigidBodyConstructionInfo
+    rbInfo(0, myMotionState, groundShape, btVector3(0,0,0));
+
+  btRigidBody* body = new btRigidBody(rbInfo);
+
+  // Add the body to the dynamics world
+  m_dynamicsWorld->addRigidBody(body);
+  */
+}
+
+/*
+extern "C" void cpp_timeStep(float delta)
+{
+  // TODO: Find what unit Bullet uses here
+  m_dynamicsWorld->stepSimulation(delta / 1000.f);
+}
+*/
+
+// Cleanup in the reverse order of creation/initialization
+extern "C" void cpp_cleanupBullet()
+{
+  // Remove the rigidbodies from the dynamics world and delete them
+  for (int i=m_collisionWorld->getNumCollisionObjects()-1; i>=0 ;i--)
+    {
+      btCollisionObject* obj = m_collisionWorld->getCollisionObjectArray()[i];
+      /*
+      btRigidBody* body = btRigidBody::upcast(obj);
+
+      if (body && body->getMotionState())
+        delete body->getMotionState();
+      */
+
+      m_collisionWorld->removeCollisionObject( obj );
+      delete obj;
+    }
+
+  // Delete collision shapes
+  /*
+  for (int j=0;j<m_collisionShapes.size();j++)
+    {
+      btCollisionShape* shape = m_collisionShapes[j];
+      delete shape;
+    }
+  */
+
+  delete m_collisionWorld;
+  //delete m_solver;
+  delete m_broadphase;
+  delete m_dispatcher;
+  delete m_collisionConfiguration;
+}

core/resource.d

@@ -334,8 +334,6 @@ struct ResourceManager
         assert(ti.bsaFile == -1);
       }
 
-    ti.ml = null;
-
     textureLookup[ti.name] = ti;
 
     return ti;
@@ -447,7 +445,6 @@ struct TextureResource
   int bsaFile;	// If set to -1, the file is in the file system
   int bsaIndex;
   char[] type;  // Texture format, eg "tga" or "dds";
-  ManualLoader ml;
 
   public:
 
@@ -460,11 +457,13 @@ struct TextureResource
     return bsaIndex == -1;
   }
 
+  /*KILLME
   // Returns true if resource is loaded
   bool isLoaded()
   {
     return ml != null;
   }
+  */
 }
 
 // OLD STUFF
@@ -495,11 +494,5 @@ struct TextureResource
 
       writefln(" Done\n");
     }
-
-  void killBSAs()
-    {
-      foreach(BSAFile f; archives)
-	delete f;
-    }
 }
 +/

dsss.conf

@@ -4,7 +4,7 @@
 
 [openmw.d]
 # Add libraries and the two C++ object files
-buildflags = -llOgreMain -llopenal -llOIS -llavcodec -llavformat cpp_ogre.o cpp_avcodec.o
+buildflags = -llOgreMain -llopenal -llOIS -llavcodec -llavformat cpp_ogre.o cpp_avcodec.o cpp_bullet.o bullet/libBulletDynamics.a bullet/libBulletCollision.a bullet/libLinearMath.a
 
 # Make sure the C++ object files are built first
 version(Windows) {
@@ -34,7 +34,7 @@ prebuild += dsss clean niftool
 [esmtool.d]
 # Because of interdepencies between the ESM code and the resource
 # manager, we have to include all the C++ stuff.
-buildflags = -llOgreMain -llopenal -llOIS -llavcodec -llavformat cpp_ogre.o cpp_avcodec.o
+buildflags = -llOgreMain -llopenal -llOIS -llavcodec -llavformat cpp_ogre.o cpp_avcodec.o cpp_bullet.o bullet/libBulletDynamics.a bullet/libBulletCollision.a bullet/libLinearMath.a
 
 
 

esm/filereader.d

@@ -557,6 +557,13 @@ struct TES3File
       file.seekCur(leftSub);
     }
 
+  // Check the name and size before skipping
+  void skipHNSub(char[] name, uint size)
+  {
+    getSubNameIs(name);
+    skipHSubSize(size);
+  }
+
   // These read an entire sub-record, including the header. They also
   // adjust and check leftSub and leftRecord variables through calling
   // getSubHeader().

esm/loadcell.d

@@ -123,9 +123,9 @@ struct ExteriorCell
 
 struct ExtCellHash
 {
-  // This is a pretty good hash, gives no collisions at all for
+  // This is a pretty good hash, gives no collisions for all of
-  // Morrowind.esm and a table size of 2048, and very few collisions
+  // Morrowind.esm when the table size is 2048, and it gives very few
-  // overall. Not that it matters of course.
+  // collisions overall. Not that it matters that much.
   static uint hash(uint val)
   {
     uint res = cast(ushort)val;
@@ -304,8 +304,7 @@ struct Land
     // Save file position
     getContext(context);
 
-    // TODO: We don't decode these yet. Se ESLand.h from
+    // Skip these here. Load the actual data when the cell is loaded.
-    // Morrowindremake for a lot of hints.
     if(isNextSub("VNML")) skipHSubSize(12675);
     if(isNextSub("VHGT")) skipHSubSize(4232);
     if(isNextSub("WNAM")) skipHSubSize(81);
@@ -342,7 +341,8 @@ struct PathGrid
     assert(state == LoadState.Unloaded);
 
     readHNExact(&data, data.sizeof, "DATA");
-    getHNString("NAME"); // Cell name, we don't really need it.
+    getHNString("NAME"); // Cell name, we don't really need it so just
+                         // ignore it.
 
     // Remember this file position
     getContext(context);
@@ -352,7 +352,7 @@ struct PathGrid
       {
 	int size = skipHSub();
 	if(size != 16*data.s2)
-	  fail("Path grid table size");
+	  fail("Path grid table size mismatch");
       }
 
     // Size varies. Path grid chances? Connections? Multiples of 4

input/events.d

@@ -33,6 +33,8 @@ import core.config;
 import scene.soundlist;
 import scene.player;
 
+import bullet.bindings;
+
 import ogre.bindings;
 
 import input.keys;
@@ -246,6 +248,10 @@ void initializeInput()
     {
       cpp_moveCamera(position[0], position[1], position[2],
 		     rotation[0], rotation[1], rotation[2]);
+
+      // Insert a collision box close to the player
+      cpp_insertBox(position[0], position[1]+500, position[2]);
+      cpp_drawBox(position[0], position[1]+500, position[2]);
     }
 
   // TODO/FIXME: This should have been in config, but DMD's module
@@ -294,29 +300,41 @@ extern(C) int d_frameStarted(float time)
   if(pause) return 1;
 
   const float moveSpeed = 900;
+  float speed = moveSpeed * time;
 
   // Check if the movement keys are pressed
   float moveX = 0, moveY = 0, moveZ = 0;
+  float x, y, z;
 
-  if(isPressed(Keys.MoveLeft)) moveX -= moveSpeed;
+  if(isPressed(Keys.MoveLeft)) moveX -= speed;
-  if(isPressed(Keys.MoveRight)) moveX += moveSpeed;
+  if(isPressed(Keys.MoveRight)) moveX += speed;
-  if(isPressed(Keys.MoveForward)) moveZ -= moveSpeed;
+  if(isPressed(Keys.MoveForward)) moveZ -= speed;
-  if(isPressed(Keys.MoveBackward)) moveZ += moveSpeed;
+  if(isPressed(Keys.MoveBackward)) moveZ += speed;
-  if(isPressed(Keys.MoveUp)) moveY += moveSpeed;
+  if(isPressed(Keys.MoveUp)) moveY += speed;
-  if(isPressed(Keys.MoveDown)) moveY -= moveSpeed;
+  if(isPressed(Keys.MoveDown)) moveY -= speed;
 
-  // Move camera. We only support "ghost-mode" at the moment, so we
+  // Move the player. This is a temporary hack, we should do this more
-  // move without physics or collision detection.
+  // efficiently in C++.
-  cpp_moveCameraRel(moveX*time, moveY*time, moveZ*time);
+  if(moveX != 0 || moveY !=0 || moveZ != 0)
+    {
+      cpp_moveCameraRel(moveX, moveY, moveZ);
+      cpp_getCameraPos(&x, &y, &z);
+      bool nw = cpp_movePlayerCollision(x, y, z, moveX, moveY, moveZ) != 0;
+
+      if(nw != collides)
+        {
+          if(nw) writefln("Entered shape");
+          else writefln("Left shape");
+          collides = nw;
+        }
+    }
 
   sndCumTime += time;
   if(sndCumTime > sndRefresh)
     {
-      float x, y, z;
       float fx, fy, fz;
       float ux, uy, uz;
 
-      cpp_getCameraPos(&x, &y, &z);
       cpp_getCameraOrientation(&fx, &fy, &fz, &ux, &uy, &uz);
 
       soundScene.update(x,y,z,fx,fy,fz,ux,uy,uz);
@@ -326,3 +344,4 @@ extern(C) int d_frameStarted(float time)
   return 1;
 }
 
+bool collides = false;

ogre/bindings.d

@@ -45,9 +45,6 @@ import core.resource;
 // these directly in D code, only pass them back to the C++ code.
 typedef void* NodePtr;
 
-// Pointer to a manual loader class in C++.
-typedef void* ManualLoader;
-
 extern(C):
 
 // Do engine configuration. Returns 0 if we should continue, 1 if
@@ -152,3 +149,6 @@ void cpp_moveCameraRel(float x, float y, float z);
 
 // Do some debug action. Check the menu for today's specials!
 void cpp_debug(int i);
+
+// Insert a 100x100x100 axis-aligned cube at x,y,z
+void cpp_drawBox(float x, float y, float z);

ogre/cpp_framelistener.cpp

@@ -146,11 +146,13 @@ extern "C" void cpp_getCameraOrientation(float *fx, float *fy, float *fz,
   *uz = up[1];
 }
 
-// Move and rotate camera in place. Transforms Morrowind coordinates
+// Move and rotate camera in place.
-// to OGRE coordinates.
 extern "C" void cpp_moveCamera(float x, float y, float z,
 			       float r1, float r2, float r3)
 {
+  // Transforms Morrowind coordinates to OGRE coordinates. The camera
+  // is not affected by the rotation of the root node, so we must
+  // transform this manually.
   mCamera->setPosition(Vector3(x,z,-y));
 
   // Rotation is probably not correct, but for now I have no reference

ogre/cpp_ogre.cpp

@@ -56,3 +56,23 @@ SceneNode *root;
 #include "cpp_bsaarchive.cpp"
 #include "cpp_interface.cpp"
 #include "cpp_overlay.cpp"
+
+// Testing
+extern "C" void cpp_drawBox(float x, float y, float z)
+{
+  // Create a plane aligned with the xy-plane.
+  /*
+    MeshManager::getSingleton().createPlane("box1",
+           ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME,
+           Plane(Vector3::UNIT_X, 0),
+	   100,100);
+    Entity *ent = mSceneMgr->createEntity( "box", "box1" );
+  */
+
+  Entity *ent = mSceneMgr->createEntity( "box", SceneManager::PT_SPHERE);
+  ent->setCastShadows(false);
+  SceneNode *nd = root->createChildSceneNode();
+  nd->attachObject(ent);
+  //nd->setScale(0.5, 0.5, 0.5);
+  nd->setPosition(x,y,z);
+}

openmw.d

@@ -31,6 +31,8 @@ import std.file;
 import ogre.ogre;
 import ogre.bindings;
 
+import bullet.bullet;
+
 import scene.celldata;
 import scene.soundlist;
 
@@ -219,10 +221,13 @@ void main(char[][] args)
     {
       // Warm up OGRE
       setupOgre();
-
-      // Clean up ogre when we're finished.
       scope(exit) cleanupOgre();
 
+      // Set up Bullet
+      initBullet();
+      scope(exit) cleanupBullet();
+
+
       if(cd.inCell)
 	{
 	  setAmbient(cd.ambi.ambient, cd.ambi.sunlight,

scene/celldata.d

@@ -39,7 +39,8 @@ import sound.audio;
 import scene.player;
 
 // Base properties common to all live objects. Currently extremely
-// sketchy.
+// sketchy. TODO: This will all be handled in Monster script at some
+// point.
 struct LiveObjectBase
 {
   // Should this stuff be in here?
@@ -92,7 +93,7 @@ struct LiveObjectBase
   // ??
   byte unam;
 
-  // Don't even get me started on script-related issues
+  // TODO: Scripts
 }
 
 // Generic version of a "live" object
@@ -223,6 +224,21 @@ class CellData
 
       loadReferences();
 
+      // TODO: Set up landscape system here.
+      /*
+      with(esFile)
+      {
+        restoreContext(exCell.land.context, reg);
+
+        // TODO: Not all of these will be present at all times
+        readHNExact(,12675, "VNML");
+        readHNExact(,4232, "VHGT");
+        readHNExact(,81, "WNAM");
+        readHNExact(,12675, "VCLR");
+        readHNExact(,512, "VTEX");
+      }
+      */
+
       const float cellWidth = 8192;
 
       // TODO/FIXME: This is temporary
@@ -243,7 +259,7 @@ class CellData
 
       esFile.restoreContext(inCell.context, reg);
 
-      // TODO: Read this crap in loadcell.d
+      // TODO: Read this in loadcell.d
       if(esFile.isNextSub("INTV") || esFile.isNextSub("WHGT"))
 	water = esFile.getHInt();
       //writefln("Water height: ", water);
@@ -555,12 +571,6 @@ class CellData
 		  }
 	      }
 	  }
-
-	// Skip this? Large chance that the same file will be used for
-	// the next cell load, and the rest of our system can handle
-	// that without closing or reopening the file.
-
-	//close(); // Close the file
       }
     }
 }
@@ -582,8 +592,9 @@ struct CellFreelist
     if(next) return list[--next];
 
     // Since these are reused, there's no waste in allocating on the
-    // stack here. Also, this is only semi-runtime (executed when
+    // heap here. Also, this is only semi-runtime (executed when
-    // loading a cell), thus a rare GC slow down is non-critical.
+    // loading a cell), thus an occational GC slow down is not
+    // critical.
     return new CellData(new RegionManager("CELL"));
   }