OpenSceneGraph

Katia Oleinik: koleinik@bu.edu

based on materials from http://www.openscenegraph.org/

Agenda:• Introduction to OpenSceneGraph• Hardware requirements• Overview of OSG structure• First example – displaying a model• Building primitives• Transformations• Using OpenGL primitives• Texture• Special nodes

Introduction to OpenSceneGraph

OpenSceneGraph

• an open source 3D graphics API (application programming interface)• used for

- visual simulation, - computer games,- scientific visualization, - modeling,- training, etc.

OpenSceneGraph

• written in C++ (encourages object oriented programming);• runs on a number of operating systems, including:

- MS Windows- Max OS X- Linux- IRIX- Solaris- Sony Playstation

uses OpenGL for rendering (allows for high performance graphics);supports the standard template library (STL);

Introduction to OpenSceneGraph

OpenSceneGraph 3.0 Features:

• Support for performance increasing featureso View frustum, small feature and occlusion cullingo Level of detail (LOD)o State sorting and lazy state updatingo OpenGL latest extensionso Multi-threading and database optimization

• Support for OpenGL, from 1.1 through 2.0 including the latest extensions• Support for OpenGL Shading Language• Support for a wide range of 2D image and 3D database formats• Loaders available for OpenFlight, TerraPage, OBJ, 3DS, JPEG, PNG and GeoTIFF• Particle effects• Support for anti-aliased TrueType text• Multi-threaded and configurable support for multiple CPU/multiple GPU machines

Introduction to OpenSceneGraph

OpenSceneGraph 3.0 latest updates:

• Support for Windows MS Visual Studio• Support for Android on tablets and phones• Support for IOS (iPhone OS) on tablets and phones• Improvements to osgVolume class enabling high quality volume rendering

Introduction to OpenSceneGraph

FightGear Flight Simulator

FightGear Flight Simulator

FightGear Flight Simulator

Hardware requirements

Processor• OSG runs on most contemporary CPUs. • OSG is thread-safe and can take advantage of multi-processor and

dual core architectures. • OSG runs on both 32- and 64-bit processors.

Graphics• OSG requires graphics hardware with robust OpenGL support• 256 MB of graphics RAM – good starting point

RAM• 1GB – good enough for many application, but you might need more,

depending on your datasetDisc

• Depends on your data requirements

Overview of OSG structure

Matrix

Matrix

Overview of OSG structure

Root

Transformation

Geode

Drawable

Transformation

Geode

Drawable

Geode

Drawable

First example – displaying a model

• ex_simple_viewer.cpp

// load the nodes from the command line arguments.

osg::Node* model = osgDB::readNodeFile(argv[1]);

// initialize the viewer and set the scene to render

osgViewer::Viewer viewer;viewer.setSceneData(model);

// run viewer

return viewer.run();

Root Node

First example – displaying a model

• ex_simple_viewer.cpp: compiling, linking and running

To compile and link% make ex_simple_viewer

To run the viewer% ex_simple_viewer cow.obj

First button – rotate the modelSecond button – translateThird button – scale

Press “q” (“Esc” for Windows) button to exit

First example – displaying a model

• ex_viewer_args.cpp

// call argument parser

osg::ArgumentParser arguments (&argc, argv);std::string filename;

// define the argument line option

arguments.read("--model", filename);

// load the nodes from the command line arguments

osg::Node* model = osgDB::readNodeFile(filename);

First example – displaying a model

• ex_viewer_args.cpp: running

To compile and link% make ex_viewer_args

To run the viewer% ex_viewer_args –-model cow.obj

Try a few different models:dumptruck.osgteapot.osg

First example – displaying a model

• Input OSG model file structureGeode { name "teapot.osg" nodeMask 0xffffffff cullingActive TRUE num_drawables 1 Geometry { DataVariance STATIC useDisplayList FALSE useVertexBufferObjects TRUE PrimitiveSets 1 { DrawArrays TRIANGLES 0 9744 }

VertexArray Vec3Array 9744 { 0.367875 -0 0.237053 0.375 -0 0.225 0.365248 0.086895 0.225

..... } ColorBinding OVERALL ColorArray Vec4Array 1 { 1 1 1 1 } }}

Building geometric primitives

• ex_simple_cone.cpp

// Create a vector to represent the "center of the cone"Vec3 vcen(xcen, ycen, zcen);osg::Cone* cone = new Cone(vcen, radius, height);

// Create a drawable object based on the coneosg::ShapeDrawable *drawable = new ShapeDrawable(cone);

// create a new geode (root node)

osg::Geode* geode = new Geode();geode->addDrawable(drawable);

Root Node

Geode

Drawable

cone

Building geometric primitives

• Improving ex_simple_cone.cpp

// Create a vector to represent the "center of the cone"osg:: Vec3 vcen(xcen, ycen, zcen);osg::Cone* cone = new Cone(vcen, radius, height);

// Create a drawable object based on the coneosg:: ShapeDrawable *drawable = new ShapeDrawable(cone);drawable->setColor(osg::Vec4(1.0f, 0.0f, 0.0f, 1.0f));

// create a new geode osg:: Geode* geode = new Geode();geode->addDrawable(drawable);

// create a root nodeosg::Group *root = new osg::Group();root->addChild(geode);

Root Node

Geode

Drawable

cone

Building geometric primitives

To compile and link% make ex_simple_cone

To run the viewer% ex_simple_cone

• ex_simple_cone.cpp

Building geometric primitives

OSG comes with a number of primitives

Box Sphere Cone Cylinder Capsule Special shapes (e.g. InfinitePlane)

• ex_simple_cone.cpp

Matrix

Matrix

Building geometric primitives• ex_arrow.cpp

// Create a cone and a cylinderGeode *make_cone( float xcen, …){}Geode *make_cylinder( float xcen, …){}

// create an arrow, as a transform node MatrixTransform* arrow = new MatrixTransform;arrow->setMatrix(Matrix::scale(1.0, 1.0, 1.0));arrow->addChild(cone); arrow->addChild(cylinder);

// add the arrow to the upper transformMatrixTransform* mt = new MatrixTransform();mt->setMatrix( Matrix::rotate(inDegrees(30.0), 1.0, 0.0, 0.0));mt->addChild(arrow);

// create a root nodeosg::Group *root = new osg::Group();root->addChild(mt);

Root Node

cone

cylinder

Transform

Transform

Building geometric primitives• Exercise Building 3 arrows

Matrix

Root Node

Transform

Matrix

cone

cylinder

TransformMatrix

cone

cylinder

TransformMatrix

cone

cylinder

Transform

Building geometric primitives• Exercise: Building 3 arrows

Group *make_vec_arrow(float shaft_radius, float total_length, float r, float g, float b)

{ float cone_radius = 2*shaft_radius; float cone_height = cone_radius; float shaft_length = total_length - cone_height; osg::Geode *cylinder = make_cylinder(0.0, 0.0, shaft_length/2.0, shaft_radius, shaft_length, r,g,b,1.0); osg::Geode *cone = make_cone(0.0, 0.0, shaft_length + cone_height/4.0, cone_radius, cone_height, r, g, b, 1.0); osg::Group* vec_arrow = new Group; vec_arrow->addChild(cylinder); vec_arrow->addChild(cone);

return vec_arrow;}

osg::Group *red_arrow = make_vec_arrow(…);osg::MatrixTransform* xaxis = new MatrixTransform;xaxis->addChild(red_arrow);xaxis->setMatrix(…);

Building geometric primitives• Reusing the geometry

Matrix

Root Node

Transform

MatrixTransform

MatrixTransform

MatrixTransform

Geode 3Geode 2Geode 1

GeometryVertices

FacesColors

Using OpenGL primitives• PrimitiveSet Class

21

4

30

Points2

1 4

3

Lines

4

32

10LineStrip

4

32

10LineLoop

Polygon

0 1

2

3

4

Triangles0 1

2

Quads

3

0

2

1

0 2 4

1 3 5

TriangleStrip

13

5 7

0 2 46

QuadStrip

0

1 2

3

4

56

TriangleFan

Using OpenGL primitives• PrimitiveSet Class

Group

Geode

Geometry

Vertices Faces Colors Texture

osg::Group *root = new osg::Group();

…

osg::Geode* primGeode = new osg::Geode();root->addChild(primGeode);

…

osg::Geometry* primGeom = new osg::Geometry();primGeode->addDrawable(primGeom);

…

viewer.setSceneData(root)

Using OpenGL primitives• PrimitiveSet Class

osg::Vec3Array* pyramidVertices = new osg::Vec3Array;pyramidVertices->push_back( osg::Vec3( 0, 0, 0) ); // front left pyramidVertices->push_back( osg::Vec3(10, 0, 0) ); // front right pyramidVertices->push_back( osg::Vec3(10,10, 0) ); // back right pyramidVertices->push_back( osg::Vec3( 0,10, 0) ); // back left pyramidVertices->push_back( osg::Vec3( 5, 5,10) ); // peak

// create primitives: quad for the baseosg::DrawElementsUInt* pyramidBase = new osg::DrawElementsUInt(osg::PrimitiveSet::QUADS, 0);pyramidBase->push_back(3);pyramidBase->push_back(2);pyramidBase->push_back(1);pyramidBase->push_back(0);

// create primitives: triangles for the sides osg::DrawElementsUInt* pyramidFaceOne = new osg::DrawElementsUInt(osg::PrimitiveSet::TRIANGLES, 0);pyramidFaceOne->push_back(0);pyramidFaceOne->push_back(1);pyramidFaceOne->push_back(4);

Using OpenGL primitives• PrimitiveSet Class

// assign all primitives to the Geometry nodeosg::Geometry* pyramidGeometry = new osg::Geometry();pyramidGeometry->setVertexArray( pyramidVertices );pyramidGeometry->addPrimitiveSet(pyramidBase);pyramidGeometry->addPrimitiveSet(pyramidFaceOne);pyramidGeometry->addPrimitiveSet(pyramidFaceTwo);pyramidGeometry->addPrimitiveSet(pyramidFaceThree);pyramidGeometry->addPrimitiveSet(pyramidFaceFour);

// create a geode and add the geometry to the geodeosg::Geode* pyramidGeode = new osg::Geode();pyramidGeode->addDrawable(pyramidGeometry);

// Create a root node and add the geodeosg::Group* root = new osg::Group();root->addChild(pyramidGeode);

Root Node

Geode

geometry

Using OpenGL primitives• PrimitiveSet Class

// create an array of colorsosg::Vec4Array* colors = new osg::Vec4Array;colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 1.0f) ); //index 0 redcolors->push_back(osg::Vec4(0.0f, 1.0f, 0.0f, 1.0f) ); //index 1 greencolors->push_back(osg::Vec4(0.0f, 0.0f, 1.0f, 1.0f) ); //index 2 bluecolors->push_back(osg::Vec4(1.0f, 1.0f, 1.0f, 1.0f) ); //index 3 white

// create an index arrayosg::TemplateIndexArray <unsigned int, osg::Array::UIntArrayType,4,4> *colorIndexArray;colorIndexArray = new osg::TemplateIndexArray<unsigned int, osg::Array::UIntArrayType,4,4>;colorIndexArray->push_back(0); // vertex 0 assigned color array element 0colorIndexArray->push_back(1); // vertex 1 assigned color array element 1colorIndexArray->push_back(2); // vertex 2 assigned color array element 2colorIndexArray->push_back(3); // vertex 3 assigned color array element 3colorIndexArray->push_back(0); // vertex 4 assigned color array element 0

// assign the arrays to the geometrypyramidGeometry->setColorArray(colors);pyramidGeometry->setColorIndices(colorIndexArray);pyramidGeometry->setColorBinding(osg::Geometry::BIND_PER_VERTEX);

Transformations

OSG allows for hierarchies of transformation node. Such structure makes it much easier to control the motions of each limb, part or the whole body.

transform

transform transform

transform

geode

geodegeode

transform

transform

transform

transform

geode

geode

geode

geode geode

Transformations

OSG MatrixTransform Class:

// direct transformation specificationtransform->getMatrix();transform->setMatrix();

// set identityIdentity();

// navigationosg::Matrix mt1 = osg::Matrix::Translate(x, y, z);osg::Matrix mt2 = osg::Matrix::Rotate(angle, x, y, z);osg::Matrix mt3 = osg::Matrix:: Scale(x, y, z);

// for multiplying matricesosg::Matrix resultMat = mt1 * t2 * mt3;

// invert matrixosg::Matrix::Invert();

AddingTexture

// initialize texture classosg::Texture2D* texture = new osg::Texture2D;texture->setDataVariance(osg::Object::DYNAMIC);

// load the texture image from the file: osg::Image* texImage = osgDB::readImageFile(texture_file);if (! texImage){ std::cout << " couldn't find texture, quiting." << std::endl; return -1;}

// Assign the texture to the image we read from file: texture->setImage(texImage);

// Create a new StateSet with default settings: osg::StateSet* stateTex = new osg::StateSet();

// Assign texture unit 0 of our new StateSet to the texture // enable the texture.stateTex->setTextureAttributeAndModes(0,texture,osg::StateAttribute::ON);

// Associate this state set with the Geode that contains// the primitive: geode->setStateSet(stateTex);

Any file format supported by the plugins

AddingTexture

// Add parsing texture option from a command line

// call argument parserosg::ArgumentParser arguments (&argc, argv);std::string filename;

// define the argument line optionarguments.read("--texture", texfilename);

osg::Texture2D* texture = new osg::Texture2D;texture->setDataVariance(osg::Object::DYNAMIC);

// load the texture image from the file: osg::Image* texImage = osgDB::readImageFile(texture_file);if (! texImage){ std::cout << " couldn't find texture, quiting." << std::endl; return -1;}…

• Exercise: Reading texture from the command line

Special Nodes

Switch node - Node for switching between different states of an object

LOD node - Rendering Optimization node

Billboard node – rendering optimization node

Text node – node for presenting text on the screen

Special Nodes

LOD (“level of detail” node - Rendering Optimization node

This node “switches” based on the distance from the viewer to the object.

It works like a regular group node: load.addChild(detailedNode);

Set the visible range from the viewer to the object:load.setRange(childNumber, near, far);

Special Nodes

LOD lod = new LOD();

Lod.addChild(detailedNode);Lod.setRange(0, 0, 10);

Lod.addChild(NotSodetailedNode);Lod.setRange(1, 10, 100);

Lod.addChild(CorseNode);Lod.setRange(2, 100, 1000);

Lod.addChild(NoDetailNode);Lod.setRange(2,1000,10000);

For up-to-date information on the project, in-depth details on how to compile and run libraries and examples, see the documentation on the OpenSceneGraph website: http://www.openscenegraph.org For support subscribe to OSG public mailing list: http://www.openscenegraph.org/projects/osg/wiki/MailingLists

or forum: http://forum.openscenegraph.org

Contact me: Katia Oleinik: koleinik@bu.edu

Tutorial presentations and examples online:www.bu.edu/tech/research/training/presentations/list/

Online evaluation:http://scv.bu.edu/survey/tutorial_evaluation.html

Autodesk Maya

Resources

• BU Scientific Computing and Visualization:

http://www.bu.edu/tech/research/scv/

• OpenSceneGraph: http://www.openscenegraph.org/