C / C++ Graphics Programming with OpenGL & OpenSceneGraph

C/C++ Graphics Programming IS&T Spring 2011

C / C++ Graphics Programming withC / C++ Graphics Programming with OpenGL & OpenSceneGraph OpenGL & OpenSceneGraph

Erik [email protected]


C / C++ Graphics ProgrammingC / C++ Graphics Programming OpenGL

– Program from scratch– Access to all graphics card features– Available on virtually all platforms

OpenSceneGraph– Higher level, built on OpenGL– Program using scene graph paradigm– Lots of utility functions


Tutorial OverviewTutorial Overview C.G. Paradigm – models, lighting, transforms, etc. OpenGL

– Overview of OpenGL– Window/events (freeglut)– Hands-on

OpenSceneGraph– Overview– Hands-on


Human view of physical worldHuman view of physical world


Human view of imageHuman view of image


Computer graphics paradigmComputer graphics paradigm


C.G. paradigm with lightC.G. paradigm with light


C.G. basic calculationC.G. basic calculation


Result is a digital imageResult is a digital image


Resulting imageResulting image


Model geometry – two cuboidsModel geometry – two cuboids


Model geometry - Model geometry - approximationapproximation


Polygonal modelsPolygonal models


Overview: lights, cameras, …Overview: lights, cameras, …


Coordinate SystemsCoordinate Systems


Camera View (Frustum)Camera View (Frustum)


Get examples; build one, build Get examples; build one, build allallLog on to katana% cp –r /scratch/ogltut .% cd ogltut% make ex_green_tri% ./ex_green_tri% make all(note that after tutorial, examples will be available via the web, but not in the location above. Go to http://scv.bu.edu/documentation/presentations/intro_to_OpenGL/ogltut )


ExampleExample

In ex_green_tri.c

void mydraw(void){ glColor3f( 0.0, 1.0, 0.0); glBegin(GL_POLYGON); glVertex3f( 0.0, 0.0, -5.0); glVertex3f( 1.0, 0.0, -5.0); glVertex3f( 1.0, 2.0, -5.0); glEnd();}


RGB color spaceRGB color space

glColor3f( 0.0, 1.0, 0.0); gives green

Colorsas RGB (red, green, blue)as RGBA (red, green, blue, alpha)

Light is additive, exampleswhite = (1.0, 1.0, 1.0);yellow = (1.0, 1.0, 0.0);


OpenGL functionsOpenGL functions

% man glColor

void glColor3d( GLdouble red, GLdouble green, GLdouble blue )void glColor3s( GLshort red, GLshort green, GLshort blue )void glColor3ub( GLubyte red, GLubyte green, GLubyte blue )void glColor4d( GLdouble red, GLdouble green, GLdouble blue, GLdouble alpha )


Try this yourself -Try this yourself -

% cp ex_green_tri.c play.c

(A)Make the triangle magenta (purple)solution: soln_magenta_tri.c

(B) Then make it into a rectanglesolution: soln_magenta_rect.c

(C) Then make the vertices different colorssolution: soln_multicolor_rect.c


OpenGL – primitivesOpenGL – primitives


OpenGL – primitive exampleOpenGL – primitive example

Let’s look at ex_quad.c


Stepping back: the main loopStepping back: the main loop

int main(int argc, char **argv){ int i; glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); glutCreateWindow("ex_quad"); glutDisplayFunc(display); init(); glutMainLoop(); return 0;}


GLUT - The OpenGL Utility Toolkit

Actually, we are using freeglut, a completely OpenSourced alternative to the OpenGL Utility Toolkit (GLUT

Allows creation and management of windows containing OpenGL contexts on a wide range of platforms

Provides event management: read mouse, keyboard and joystick functions.

An 'idle' routine and timers A simple, cascading pop-up menu facility Utility routines to generate various solid and wire frame objects Support for bitmap and stroke fonts Miscellaneous window management functions Freeglut does not require glutMainLoop() !


Example of changes in display()

Run ex_quad_motion

void mydraw(void){ static int nframe = 0; float xoffset; xoffset = sin((double)nframe/240.0); drawstuff(xoffset); nframe++;}


Better way: OpenGL transformations

void mydraw(void) [ex_translate.c]{ static float time = 0.0; float xoffset; time = glutGet(GLUT_ELAPSED_TIME) / 1000.0; xoffset = sin((double)(M_PI*time)); glPushMatrix(); glTranslatef(xoffset, 0.0, 0.0); drawstuff(); glPopMatrix(); glutPostRedisplay();}


Rotation using OpenGL transform

void mydraw(void) [ex_rotate.c]{ static float time = 0.0; float xoffset; time = glutGet(GLUT_ELAPSED_TIME) / 1000.0; xoffset = sin((double)(M_PI*time)); glPushMatrix(); glTranslatef(xoffset, 0.0, 0.0); drawstuff(); glPopMatrix(); glutPostRedisplay();}


Translation and rotation in 2DTranslation and rotation in 2D

(B) Rotate (B) Rotate by 45 degreesby 45 degrees TranslateTranslate by (7.0, 4.0)by (7.0, 4.0)

(A) Translate(A) Translate by (5.0, 1.0)by (5.0, 1.0)


Composition of transformationsComposition of transformations

Rotate 45 degrees CCW Translate (2, 0) Rotate 45 degrees CCW Translate (2, 0)


Composition of transformationsComposition of transformations

Translate (2, 0) Rotate 45 degrees CCW Translate (2, 0) Rotate 45 degrees CCW


CompareCompare

Rotate firstRotate firstThen translateThen translate

Translate firstTranslate firstThen rotateThen rotate

BPC: Art and Computation – Spring 2007 33

Rotations in 3DRotations in 3D


Translations in 3DTranslations in 3DSphereSphere translated bytranslated by (-3.0, 2.0, -4.5)(-3.0, 2.0, -4.5) Blue cubeBlue cube translated bytranslated by (2.0, 0.0, -4.0)(2.0, 0.0, -4.0) rotated 60 degrotated 60 deg around y-axisaround y-axis

Purple cubePurple cube translated bytranslated by (0.0, 0.0, 0.0)(0.0, 0.0, 0.0)


Camera location setupCamera location setupgluLookat(xeye, yeye, zeye, xat, yat, zat, xup, yup, zup)


Camera perspective setupCamera perspective setup


Full view / transform pipeline


Your turnYour turn Modify ex_lookat.c so that you can so the sphere through

the hole in the torus.

Now change it so that “z” is up.


Other transformations - scalingOther transformations - scaling


Multiple transformations Example in ex_multi_transform.c


Transform Exercise

Modify ex_multi_transform.c so that there are bouncing tetrahedra on all four corners of the platform.

Solution: soln_four_bounce.c


Transform Challenge

Modify ex_rotate.c so strips rotate about the vertical axis going through x=2.0 and z = 0.0

Solution: soln_rotate_challenge.c


Back to lightingBack to lighting

V_eye = P_eye - PV_light = P_light - P

V_eye = (4, 1, 10) - (5, 2, 3) = (-1, -1, 7)V_light = (3, 7, 2) – (5, 2, 3) = (-2, 5, -1)


Unit shading vectorsUnit shading vectors

n = surface normal vectoru_light = unit vector to light pointu_eye = unit vector to view point


ShadingShadingambient

diffuse

specular


Shading at vertices, Shading at vertices, interpolationinterpolation


Flat shading vs Gouraud Flat shading vs Gouraud shadingshading


C.G. example - texture mapC.G. example - texture map


Texture map fullTexture map full

++


OpenGL Helpful MaterialsOpenGL Helpful Materials http://www.opengl.org http://www.freeglut.org Examples from this tutorial

– http://scv.bu.edu/documentation/presentations/intro_to_OpenGL/ogltut

Examples from opengl.org– http://scv.bu.edu/documentation/presentations/

intro_to_OpenGL/opengl.org_examples/ Many books on OpenGL


OpenSceneGraphOpenSceneGraph

Open source OpenGL based Similar to SGI Performer Many utility functions

– Notably, 3-D file readers


Get examples; build allGet examples; build all

Log on to katana% cp –r /scratch/osgtut .% cd osgtut% make all

(note that after tutorial, examples will be available via the web, but not in the location above. On the web: http://scv.bu.edu/documentation/presentations/intro_to_OSG/osgtut )


Setting environment variablesSetting environment variables

Instead of using “run_osg” can do this:

% setenv OSG_NOTIFY_LEVEL FATAL% setenv LD_LIBRARY_PATH \ /usr/local/OpenSceneGraph/lib % ex_cone


First osg exampleFirst osg example Try running: % run_osg ex_simple_viewer cow.obj ex_simple_viewer.cpp // load the nodes from the commandline arguments. osg::Node* model = osgDB::readNodeFile(argv[1]);

// initialize the viewer and set the scene to render osgViewer::Viewer viewer; viewer.setSceneData(model); viewer.setCameraManipulator(new osgGA::TrackballManipulator());

// normal viewer usage. return viewer.run();


A few improvementsA few improvements ex_simple_viewer_better.cpp // tilt the scene to give better default eye position rootnode->setMatrix(osg::Matrix::rotate (osg::inDegrees(30.0f),1.0f,0.0f,0.0f));

// run optimization over the scene graph osgUtil::Optimizer optimzer; optimzer.optimize(rootnode);


Example, making geometryExample, making geometry ex_cone.cpp // Create a vector to represent the "center of the cone" Vec3 vcen(xcen, ycen, zcen); Cone* cone = new Cone(vcen, radius, height);

// Create a drawable object based on the cone ShapeDrawable *drawable = new ShapeDrawable(cone); drawable->setColor(Vec4(color[0], color[1], color[2], color[3])); Geode* geode = new Geode(); geode->addDrawable(drawable);


Example, combining geometryExample, combining geometry ex_arrow.cpp

MatrixTransform* arrow = new MatrixTransform;arrow->setMatrix(Matrix::scale(1.0, 1.0, 1.0));arrow->addChild(cone);arrow->addChild(cylinder);


Your turnYour turn % cp ex_arrow.c play_long_arrow.cpp Modify to make the arrow twice as long % make play_long_arrow Solution: soln_long_arrow.cpp


A bit more about scaling & transformsA bit more about scaling & transforms


Solving this scaling problemSolving this scaling problem ex_vec_arrow.cppmake_vec_arrow(shaft_radius, total_length, r, g, b)

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


ExerciseExercise % cp ex_vec_arrow.c play_axes.cpp Modify play_axes.cpp to display three unit-length arrows

at the origin – First is RED point in the +X direction– Second is GREEN point in the +Y direction– Third is BLUE point in the +Z direction

% make play_axes.cpp Solution: soln_axes.cpp


ExerciseExercise % cp ex_animated_arrow.c play_two_animated_arrows.cpp Modify play_two_animated_arrows.cpp so that the cyan

(blue-green) arrow is tangent to (pointing in) the direction of motion

% make play_two_animated_arrows.cpp Solution: soln_two_animated_arrows.cpp


““Cloning”Cloning” ex_twin_arrows.cpp

transform1 = new MatrixTransform(Matrix::translate(2, 2, 0));transform1->addChild(arrow);transform2 = new MatrixTransform(Matrix::translate(-2, -2, 0));transform2->addChild(arrow);rootnode->addChild(transform1);rootnode->addChild(transform2);


ExerciseExercise Modify the last example, so that you can animate the

PositionAttitudeTransform “arrow” and see what happens … Solution is left to you


OpenSceneGraph resourcesOpenSceneGraph resources http://www.openscenegraph.org

– http://www.openscenegraph.org/documentation/OpenSceneGraphReferenceDocs/

Examples– katana: /usr/local/OpenSceneGraph/examples– http://scv.bu.edu/documentation/presentations/intro_to_OSG/

osgtut Books

– OpenSceneGraph Quick Start Guide– OpenSceneGraph Reference Guides

New book– OpenSceneGraph 3.0: Beginner's Guide


SCV relatedSCV related Please fill out an online evaluation of this tutorial:

scv.bu.edu/survey/spring11tut_survey.html- or a paper one (I have copies)

System [email protected], [email protected]

Web-based tutorials www.bu.edu/tech/research/tutorials

Consultation by appointmentErik Brisson ([email protected])

C / C++ Graphics Programming with OpenGL & OpenSceneGraph

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