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 Post subject: Debug Drawer
PostPosted: Fri Dec 30, 2016 7:08 am 

Joined: Fri Dec 30, 2016 6:18 am
Posts: 3

i am beginner for bullet, i am implementing collision detection between Aircraft and Terrain.i added Aircraft and Terrain as collision objects to collision world.while detecting collision i want to find which part of Aircraft is touching the terrain, for this i found that we can use "debug draw class" for debugging but i don't know how to use ?

anyone can provide some sample working code for debug draw class ?

 Post subject: Re: Debug Drawer
PostPosted: Fri Dec 30, 2016 12:18 pm 

Joined: Thu Dec 08, 2016 11:46 pm
Posts: 5
I think the most important factors for answering your question are missing: (a) What language you're using, and (b) What graphics library you're using. But let's see what we can do because it *is* a little confusing at first and the wiki isn't terribly helpful here today. I am using C++ and Ogre3d 2.1 graphics.

The first thing to note is that btIDebugDraw isn't magic. It won't just draw the shapes for you *somehow* (dumb, but this was my first impression for some reason).

You need to make a class that derives from btIDebugDraw. Bullet will store your debug drawer object like this: btDynamicsWorld::setDebugDrawer( my_custom_dbg_drawer ). Then, after btDynamicsWorld::stepSimulation(), call btDynamicsWorld::debugDrawWorld(). During that function, Bullet will call btIDebugDraw::drawLine(), btIDebugDraw::drawTriangle(), btIDebugDraw::drawContactPoint(), btIDebugDraw::draw3dText(), etc on your DebugDrawer, filling my_custom_dbg_drawer with all of the information you need to build the visuals. I then use an Ogre3d FrameListener to draw the debug shapes every frame, based on the info I got from the btIDebugDraw::drawWhatever() calls. Mine is a Singleton class; here's how I set it up:

DebugDrawer dbg_drawer = &DebugDrawer::getSingleton();   // DebugDrawer derives btIDebugDraw, see below for my definition
dbg_drawer->setDebugMode( btIDebugDraw::DBG_DrawWireframe + btIDebugDraw::DBG_DrawContactPoints + btIDebugDraw::DBG_DrawConstraints + btIDebugDraw::DBG_DrawConstraintLimits );
dbg_drawer->debugPhysics( false );
bt_app.getWorld()->setDebugDrawer( dbg_drawer );
show_debug_drawer = true;
DebugDrawer::getSingleton().debugPhysics( show_debug_drawer );

I have copy-pasted my DebugDrawer mostly from Ogre3d Forums Thread: [2.1] btOgre. Note that it also derives from Ogre::FrameListener, which allows Ogre to call DebugDrawer::frameStarted() and DebugDrawer::frameEnded() during each frame, and that's where I do my actual drawing. Each graphics library will have its own way of calling frames and drawing polygons. I want to say that BulletPhysics ships with an OpenGL btIDebugDraw implementation, but I couldn't quickly find it. Try Thread: btIDebugDraw with OpenGL 4.4 - [SOLVED].

class DebugDrawer: public btIDebugDraw, public Ogre::FrameListener{
   static DebugDrawer &getSingleton(){
      static DebugDrawer instance;
      return instance;
   void init(){
      sceneManager = Ogre::Root::getSingletonPtr()->getSceneManager( "SceneManager" );   // Dangerous!  Shouldn't this grab <the first scenemanager>?
      isDebuggingPhysics = false;

      Ogre::HlmsManager *hlms_man = Ogre::Root::getSingletonPtr()->getHlmsManager();
      Ogre::HlmsUnlit *unlit_hlms = static_cast<Ogre::HlmsUnlit*>(hlms_man->getHlms( Ogre::HLMS_UNLIT ));
      Ogre::String datablockName = "DebugLineMat";
      Ogre::HlmsUnlitDatablock *datablock = static_cast<Ogre::HlmsUnlitDatablock*>(unlit_hlms->createDatablock( datablockName,
         Ogre::HlmsParamVec() ));

      vertexCount = 1000000;

      Ogre::Root *root = Ogre::Root::getSingletonPtr();
      Ogre::RenderSystem *renderSystem = root->getRenderSystem();
      Ogre::VaoManager *vaoManager = renderSystem->getVaoManager();

      Ogre::MeshPtr mesh = Ogre::MeshManager::getSingleton().createManual( "PhysicsDebuggingMesh", Ogre::ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME );

      Ogre::SubMesh *subMesh = mesh->createSubMesh();

      Ogre::VertexElement2Vec vertexElements;
      vertexElements.push_back( Ogre::VertexElement2( Ogre::VET_FLOAT3, Ogre::VES_POSITION ) );
      vertexElements.push_back( Ogre::VertexElement2( Ogre::VET_FLOAT3, Ogre::VES_DIFFUSE ) );

      size_t vertexSize = vaoManager->calculateVertexSize( vertexElements );

      Ogre::Real* vertexData = static_cast<Ogre::Real*>(OGRE_MALLOC_SIMD( vertexSize * vertexCount, Ogre::MEMCATEGORY_GEOMETRY ));

      Ogre::VertexBufferPackedVec vertexBuffers;

      pVertexBuffer = vaoManager->createVertexBuffer( vertexElements, vertexCount, Ogre::BT_DYNAMIC_PERSISTENT, vertexData, false );
      vertexBuffers.push_back( pVertexBuffer );

      Ogre::VertexArrayObject *vao = vaoManager->createVertexArrayObject( vertexBuffers, 0, Ogre::v1::RenderOperation::OT_LINE_LIST );

      subMesh->mVao[0].push_back( vao );
      subMesh->mVao[1].push_back( vao );

      mesh->_setBounds( Ogre::Aabb::BOX_INFINITE );

      item = sceneManager->createItem( mesh, Ogre::SCENE_DYNAMIC );
      item->setDatablock( datablock );
      item->setCastShadows( false );
      Ogre::SceneNode *sceneNode = sceneManager->getRootSceneNode( Ogre::SCENE_DYNAMIC )->createChildSceneNode( Ogre::SCENE_DYNAMIC );
      sceneNode->attachObject( item );

      debugModes = (DebugDrawModes)DBG_DrawWireframe;
   void deinit(){
      if( isDebuggingPhysics ) debugPhysics( false );
   void debugPhysics( bool enable ){
      isDebuggingPhysics = enable;
      if( isDebuggingPhysics ){
         item->setVisible( true );
         Ogre::Root::getSingleton().addFrameListener( this );
         item->setVisible( false );
         Ogre::Root::getSingleton().removeFrameListener( this );
   virtual void drawLine( const btVector3 &from, const btVector3 &to, const btVector3 &color ){
      if( !isDebuggingPhysics ) return;

      if( pVertexBuffer->isCurrentlyMapped() ){
         meshVertices[vertIndex++] = from.x();
         meshVertices[vertIndex++] = from.y();
         meshVertices[vertIndex++] = from.z();

         meshVertices[vertIndex++] = color.getX();
         meshVertices[vertIndex++] = color.getY();
         meshVertices[vertIndex++] = color.getZ();

         meshVertices[vertIndex++] = to.x();
         meshVertices[vertIndex++] = to.y();
         meshVertices[vertIndex++] = to.z();

         meshVertices[vertIndex++] = color.getX();
         meshVertices[vertIndex++] = color.getY();
         meshVertices[vertIndex++] = color.getZ();
   virtual void drawTriangle( const btVector3 &v0, const btVector3 &v1, const btVector3 &v2, const btVector3 &color, btScalar ){ (void)v0; (void)v1; (void)v2; (void)color; }
   virtual void drawContactPoint( const btVector3 &PointOnB, const btVector3 &normalOnB, btScalar distance, int lifeTime, const btVector3 &color ){ (void)PointOnB; (void)normalOnB; (void)distance; (void)lifeTime; (void)color; }
   virtual void reportErrorWarning( const char *warningString ){ (void)warningString; }
   virtual void draw3dText( const btVector3 &location, const char *textString ){ (void)location; (void)textString; }
   virtual void setDebugMode( int debugMode ){ debugModes = (DebugDrawModes)debugMode; }
   virtual int getDebugMode() const{ return debugModes; }

   bool frameStarted( const Ogre::FrameEvent& evt ){
      vertIndex = 0;
      meshVertices = reinterpret_cast<Ogre::Real*>(pVertexBuffer->map( 0, pVertexBuffer->getNumElements() ));
      return true;
   bool frameEnded( const Ogre::FrameEvent& evt ){
      if( pVertexBuffer->isCurrentlyMapped() ) pVertexBuffer->unmap( Ogre::UO_KEEP_PERSISTENT );
      return true;

   //DebugDrawer( DebugDrawer const& ); //don't implement!
   //void operator=( DebugDrawer const& ); //don't implement!

   Ogre::SceneManager* sceneManager;
   DebugDrawModes debugModes;

   bool isDebuggingPhysics;

   Ogre::VertexBufferPacked *pVertexBuffer;
   int vertexCount;
   Ogre::Item *item;
   Ogre::Real* meshVertices;
   int vertIndex;

See Thread: Pendulums Won't Swing! for a taste of what the DebugDrawer looks like on my machine (and let me know if you can help with constraints!).

 Post subject: Re: Debug Drawer
PostPosted: Sat Dec 31, 2016 11:01 am 

Joined: Fri Dec 30, 2016 6:18 am
Posts: 3
Thank you i am Coding in c++ only and bullet Version also same

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