1. C / C++ Graphics Programming with OpenGL & OpenSceneGraph
Erik Brisson
C/C++ Graphics Programming IS&T Spring 2011

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

3. C/C++ Graphics Programming IS&T Spring 2011
Tutorial Overview
C.G. Paradigm – models, lighting, transforms, etc.
OpenGL
Overview of OpenGL
Window/events (freeglut)
Hands-on
OpenSceneGraph
Overview
C/C++ Graphics Programming IS&T Spring 2011

4. Human view of physical world
We will encounter waves in many contexts in nature. Energy and matter closely related (deep physics) Frequency and amplitude
Waves hit objects and reflected/bounced in complex ways
C/C++ Graphics Programming IS&T Spring 2011

5. C/C++ Graphics Programming IS&T Spring 2011
Human view of image
We will encounter waves in many contexts in nature. Energy and matter closely related (deep physics) Frequency and amplitude
Waves hit objects and reflected/bounced in complex ways
C/C++ Graphics Programming IS&T Spring 2011

6. Computer graphics paradigm
When can change when it passes through materials, e.g. colored filters
Plane = flat sheet/surface
C/C++ Graphics Programming IS&T Spring 2011

7. C/C++ Graphics Programming IS&T Spring 2011
C.G. paradigm with light
C/C++ Graphics Programming IS&T Spring 2011

8. C/C++ Graphics Programming IS&T Spring 2011
C.G. basic calculation
C/C++ Graphics Programming IS&T Spring 2011

9. Result is a digital image
C/C++ Graphics Programming IS&T Spring 2011

10. C/C++ Graphics Programming IS&T Spring 2011
Resulting image
How we see in 3D
Multiple depth cues: Lighting/shading, shadows, reflections, movement
Stereopsis from two eyes (binocular vision) is fundamental. Principles of stereopsis know to Euclid (~300 BC)
Demo with Rubik’s cube
C/C++ Graphics Programming IS&T Spring 2011

11. Model geometry – two cuboids
How we see in 3D
Multiple depth cues: Lighting/shading, shadows, reflections, movement
Stereopsis from two eyes (binocular vision) is fundamental. Principles of stereopsis know to Euclid (~300 BC)
Demo with Rubik’s cube
C/C++ Graphics Programming IS&T Spring 2011

12. Model geometry - approximation
How we see in 3D
Multiple depth cues: Lighting/shading, shadows, reflections, movement
Stereopsis from two eyes (binocular vision) is fundamental. Principles of stereopsis know to Euclid (~300 BC)
Demo with Rubik’s cube
C/C++ Graphics Programming IS&T Spring 2011

13. C/C++ Graphics Programming IS&T Spring 2011
Polygonal models
C/C++ Graphics Programming IS&T Spring 2011 13

14. Overview: lights, cameras, …
C/C++ Graphics Programming IS&T Spring 2011 14

15. C/C++ Graphics Programming IS&T Spring 2011
Coordinate Systems
C/C++ Graphics Programming IS&T Spring 2011 15

16. C/C++ Graphics Programming IS&T Spring 2011
Camera View (Frustum)
C/C++ Graphics Programming IS&T Spring 2011 16

17. Get examples; build one, build all
Log 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 )
C/C++ Graphics Programming IS&T Spring 2011

18. C/C++ Graphics Programming IS&T Spring 2011
Example
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(); }
C/C++ Graphics Programming IS&T Spring 2011 18

19. C/C++ Graphics Programming IS&T Spring 2011
RGB color space
glColor3f( 0.0, 1.0, 0.0); gives green
Colors
as RGB (red, green, blue)
as RGBA (red, green, blue, alpha)
Light is additive, examples
white = (1.0, 1.0, 1.0);
yellow = (1.0, 1.0, 0.0);
C/C++ Graphics Programming IS&T Spring 2011 19

20. C/C++ Graphics Programming IS&T Spring 2011
OpenGL 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 blue,
GLdouble alpha )
C/C++ Graphics Programming IS&T Spring 2011 20

21. C/C++ Graphics Programming IS&T Spring 2011
Try this yourself -
% cp ex_green_tri.c play.c
Make the triangle magenta (purple)
solution: soln_magenta_tri.c
(B) Then make it into a rectangle
solution: soln_magenta_rect.c
(C) Then make the vertices different colors
solution: soln_multicolor_rect.c
C/C++ Graphics Programming IS&T Spring 2011 21

22. C/C++ Graphics Programming IS&T Spring 2011
OpenGL – primitives
C/C++ Graphics Programming IS&T Spring 2011 22

23. OpenGL – primitive example
Let’s look at ex_quad.c
C/C++ Graphics Programming IS&T Spring 2011 23

24. Stepping 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; }
C/C++ Graphics Programming IS&T Spring 2011 24

25. 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() !
C/C++ Graphics Programming IS&T Spring 2011

26. 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++; }
C/C++ Graphics Programming IS&T Spring 2011

27. Better way: OpenGL transformations
void mydraw(void) [ex_translate.c] { static float time = 0.0; float xoffset; time = glutGet(GLUT_ELAPSED_TIME) / ; xoffset = sin((double)(M_PI*time)); glPushMatrix(); glTranslatef(xoffset, 0.0, 0.0); drawstuff(); glPopMatrix(); glutPostRedisplay(); }
C/C++ Graphics Programming IS&T Spring 2011 27

28. Rotation using OpenGL transform
void mydraw(void) [ex_rotate.c] { static float time = 0.0; float xoffset; time = glutGet(GLUT_ELAPSED_TIME) / ; xoffset = sin((double)(M_PI*time)); glPushMatrix(); glTranslatef(xoffset, 0.0, 0.0); drawstuff(); glPopMatrix(); glutPostRedisplay(); }
C/C++ Graphics Programming IS&T Spring 2011 28

29. Translation and rotation in 2D
(B) Rotate
by 45 degrees
Translate
by (7.0, 4.0)
(A) Translate
by (5.0, 1.0)
C/C++ Graphics Programming IS&T Spring 2011

30. Composition of transformations
Rotate 45 degrees CCW Translate (2, 0)
C/C++ Graphics Programming IS&T Spring 2011

31. Composition of transformations
Translate (2, 0) Rotate 45 degrees CCW
C/C++ Graphics Programming IS&T Spring 2011

32. C/C++ Graphics Programming IS&T Spring 2011
Compare
Rotate first
Then translate
Translate first
Then rotate
C/C++ Graphics Programming IS&T Spring 2011

33. BPC: Art and Computation – Spring 2007
Rotations in 3D
BPC: Art and Computation – Spring 2007

34. BPC: Art and Computation – Spring 2007
Translations in 3D
Sphere
translated by
(-3.0, 2.0, -4.5)
Blue cube
(2.0, 0.0, -4.0)
rotated 60 deg
around y-axis
Purple cube
(0.0, 0.0, 0.0)
BPC: Art and Computation – Spring 2007

35. BPC: Art and Computation – Spring 2007
Camera location setup
gluLookat(xeye, yeye, zeye, xat, yat, zat, xup, yup, zup)
BPC: Art and Computation – Spring 2007

36. Camera perspective setup
BPC: Art and Computation – Spring 2007

37. Full view / transform pipeline
C/C++ Graphics Programming IS&T Spring 2011

38. C/C++ Graphics Programming IS&T Spring 2011
Your 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.
C/C++ Graphics Programming IS&T Spring 2011

39. Other transformations - scaling
C/C++ Graphics Programming IS&T Spring 2011

40. Multiple transformations
Example in ex_multi_transform.c
C/C++ Graphics Programming IS&T Spring 2011

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

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

43. BPC: Art and Computation – Spring 2007
Back to lighting
We will encounter waves in many contexts in nature. Energy and matter closely related (deep physics) Frequency and amplitude
Waves hit objects and reflected/bounced in complex ways
V_eye = (4, 1, 10) - (5, 2, 3)
= (-1, -1, 7)
V_light = (3, 7, 2) – (5, 2, 3)
= (-2, 5, -1)
V_eye = P_eye - P
V_light = P_light - P
BPC: Art and Computation – Spring 2007

44. BPC: Art and Computation – Spring 2007
Unit shading vectors
We will encounter waves in many contexts in nature. Energy and matter closely related (deep physics) Frequency and amplitude
Waves hit objects and reflected/bounced in complex ways
n = surface normal vector
u_light = unit vector to light point
u_eye = unit vector to view point
BPC: Art and Computation – Spring 2007

45. BPC: Art and Computation – Spring 2007
Shading
ambient
diffuse
specular
BPC: Art and Computation – Spring 2007

46. Shading at vertices, interpolation
BPC: Art and Computation – Spring 2007

47. Flat shading vs Gouraud shading
BPC: Art and Computation – Spring 2007

48. C.G. example - texture map
How we see in 3D
Multiple depth cues: Lighting/shading, shadows, reflections, movement
Stereopsis from two eyes (binocular vision) is fundamental. Principles of stereopsis know to Euclid (~300 BC)
Demo with Rubik’s cube
BPC: Art and Computation – Spring 2007

49. BPC: Art and Computation – Spring 2007
Texture map full +
How we see in 3D
Multiple depth cues: Lighting/shading, shadows, reflections, movement
Stereopsis from two eyes (binocular vision) is fundamental. Principles of stereopsis know to Euclid (~300 BC)
Demo with Rubik’s cube 
BPC: Art and Computation – Spring 2007

50. OpenGL Helpful Materials
Examples from this tutorial
Examples from opengl.org
Many books on OpenGL
C/C++ Graphics Programming IS&T Spring 2011

51. C/C++ Graphics Programming IS&T Spring 2011
OpenSceneGraph
Open source
OpenGL based
Similar to SGI Performer
Many utility functions
Notably, 3-D file readers
C/C++ Graphics Programming IS&T Spring 2011

52. Get 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: )
C/C++ Graphics Programming IS&T Spring 2011

53. Setting 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
C/C++ Graphics Programming IS&T Spring 2011

54. C/C++ Graphics Programming IS&T Spring 2011
First 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();
C/C++ Graphics Programming IS&T Spring 2011

55. C/C++ Graphics Programming IS&T Spring 2011
A 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);
C/C++ Graphics Programming IS&T Spring 2011

56. Example, 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);
C/C++ Graphics Programming IS&T Spring 2011

57. Example, 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);
C/C++ Graphics Programming IS&T Spring 2011

58. C/C++ Graphics Programming IS&T Spring 2011
Your 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
C/C++ Graphics Programming IS&T Spring 2011

59. A bit more about scaling & transforms
C/C++ Graphics Programming IS&T Spring 2011

60. Solving this scaling problem
ex_vec_arrow.cpp
make_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);
C/C++ Graphics Programming IS&T Spring 2011

61. C/C++ Graphics Programming IS&T Spring 2011
Exercise
% 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
C/C++ Graphics Programming IS&T Spring 2011

62. C/C++ Graphics Programming IS&T Spring 2011
Exercise
% 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
C/C++ Graphics Programming IS&T Spring 2011

63. C/C++ Graphics Programming IS&T Spring 2011
“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);
C/C++ Graphics Programming IS&T Spring 2011

64. C/C++ Graphics Programming IS&T Spring 2011
Exercise
Modify the last example, so that you can animate the PositionAttitudeTransform “arrow” and see what happens …
Solution is left to you
C/C++ Graphics Programming IS&T Spring 2011

65. OpenSceneGraph resources
Examples
katana: /usr/local/OpenSceneGraph/examples
Books
OpenSceneGraph Quick Start Guide
OpenSceneGraph Reference Guides
New book
OpenSceneGraph 3.0: Beginner's Guide
C/C++ Graphics Programming IS&T Spring 2011

66. C/C++ Graphics Programming IS&T Spring 2011
SCV 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 help
Web-based tutorials
Consultation by appointment
Erik Brisson
C/C++ Graphics Programming IS&T Spring 2011