Debug Drawer

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Posts: 4
Joined: Fri Dec 30, 2016 6:18 am

Debug Drawer

Post by jayasimha » Fri Dec 30, 2016 7:08 am


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 ?

Posts: 5
Joined: Thu Dec 08, 2016 11:46 pm

Re: Debug Drawer

Post by skosh2 » Fri Dec 30, 2016 12:18 pm

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:

Code: Select all

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].

Code: Select all

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!).

Posts: 4
Joined: Fri Dec 30, 2016 6:18 am

Re: Debug Drawer

Post by jayasimha » Sat Dec 31, 2016 11:01 am

Thank you i am Coding in c++ only and bullet Version also same

Posts: 2
Joined: Sat Feb 25, 2017 9:29 am

Re: Debug Drawer

Post by virginialuther12 » Sat Feb 25, 2017 9:55 am

Thank you

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