1. Lecture 02: OpenGL (Fixed-Function)
COMP 175: Computer Graphics
January 29, 2016

2. Note on Event-Based Programming
What is event-based programming?
Infinite loop until user clicks on “exit”
During that time, the system reacts to events
Keyboard, mouse
Network traffic
Threads
The most relevant for visualization/graphics are:
Repaint event
Idle event

3. What is OpenGL? Conceptual Graphics Framework
Graphics Library can be Direct3D, Java3D, OpenGL, etc.
It is a software API that controls the functions of a piece of hardware – the graphics card.
Can we run OpenGL programs remotely? (e.g., use linux.cs.tufts.edu remotely through SSH and X-tunneling?)
Graphics
System/
GPU
Application
Model
(database)
Software
Hardware
program
Library

4. In Immediate-Mode Fixed-Function mode, OpenGL acts as a state machine.
Graphics Library
In Immediate-Mode Fixed-Function mode, OpenGL acts as a state machine.
What is a state machine?
Every variable is a “global variable”
For example, the current color
You need to keep track of the states… Or query the graphics card if you forget
Which, of course, is slow

5. State Variables Pseudo code: SetState (LineStyle, DASHED);
SetState (LineColor, RED);
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
SetState (LineColor, BLUE);
DrawLine ( PtStart = (x2,y2), PtEnd = (x3,y3) );
SetState (LineStyle, SOLID);
DrawLine ( PtStart = (x3,y3), PtEnd = (x1,y1) );
What color and shape?
What color and shape?
What color and shape?

6. State Variables Pseudo code: SetState (LineStyle, DASHED);
SetState (LineColor, RED);
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
SetState (LineColor, BLUE);
DrawLine ( PtStart = (x2,y2), PtEnd = (x3,y3) );
SetState (LineStyle, SOLID);
DrawLine ( PtStart = (x3,y3), PtEnd = (x1,y1) );
What color and shape?
What color and shape?
What color and shape?

7. State Variables – Pros and Cons
What if…?
function DrawDashedTriangle (pt1,pt2,p3) {
SetState( LineStyle, DASHED );
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 ); }
What color is the triangle?
Pros:??
Cons:??

8. State Variables – Pros and Cons
What if…?
function DrawDashedTriangle (pt1,pt2,p3) {
SetState( LineStyle, DASHED );
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 ); }
What color is the triangle?
Pros: trickle down effect, caller can control the subroutine’s behavior
Cons: the color is undefined! Who set my color?!

9. State Variables – Pros and Cons
What’s right and what’s wrong with this?
function DrawTriangle (pt1,pt2,p3,
int origColor, int curColor,
int origStyle, int curStyle ) {
SetState( LineStyle, curStyle );
SetState(LineColor, curColor);
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 );
SetState( LineStyle, origStyle );
SetState(LineColor, origColor); }

10. Still A Pain, but Cleaner…
Bundles and unsets…
function DrawRedDashedTriangle(pt1,pt2,p3){
PushAttributeState();
SetState( LineStyle, DASHED );
SetState( LineColor, RED );
...
PopAttributeState(); }
This eliminates the state variable problem.

11. Another Example What does this function do?
//using idleFunc as the main render loop
void idleFunc () {
glTranslate3f (1, 0, 0);
glBegin(GL_POINTS);
glVertex3f (0, 0, 0);
glEnd(); }
Where is the point showing up?
How do I get that value?

12. What if I forget to set some state?
Forgetting the State?
What if I forget to set some state?
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
What if I set the wrong state?
SetState(LineStyle, );
DrawLine( PtStart=pt1, PtStart=p2 );
What if I forget the state a variable is in?

13. Forgetting the State? What if I forget to set some state?
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
OpenGL provides some good default values. For example, for color, it’s set to (1,1,1,1) – non transparent white
How do I know if something worked?
SetState(LineStyle, );
DrawLine( PtStart=pt1, PtStart=p2 );
You don’t. Since it’s not clear if some configuration of states will send OpenGL spinning, if you suspect an error from OpenGL, call
Glenum glGetError(void)
What if I forget the state a variable is in?
You should use this sparingly… But you can use
void glGetBooleanv(Glenum paraname, Glboolean* params)
void glGetFixedv(Glenum paraname, Glfixed* params)
void glGetFloatv(Glenum paraname, Glfloat* params)
void glGetIntegerv(Glenum paraname, Glint* params)

14. Programming Strategies?
What do you think is the best way to deal with the state machine and maintain state variables?
How to access local variables (that correspond to state variables)?
Efficiency considerations?
How do you think the programming with a state machine affects multi-threaded applications?

15. For Example
How many parameters do you have to pass to render an object?
void render () {
obj1->drawSelf(myMouse, myScreenSize, myTimer, ...);
obj2->drawSelf(myMouse, myScreenSize, myTimer, ...);
obj3->drawSelf(myMouse, myScreenSize, myTimer, ...); }
How do you enforce that there is only one instance of myMouse, myScreenSize, myTimer in code?

16. Use mutual references. For example:
Possible Answers?
Use global variables
Use mutual references. For example:
void setChild (CWidget* child) {
myChild = child;
child->setParent(this); }
MyMouse* getMouse() {
return myMouse;
void setParent (PWidget* parent) {
myParent = parent; }
void doStuff ()
MyMouse mouse =
myParent->getMouse();
doStuffWithMouse (mouse);

17. One possible answer is to use Singletons
Possible Answers?
Problems:
Need to guarantee a single instance of the states
Don’t want to pass a billion parameters during the execution of every child object
Don’t want the child to have to call parent->parent->parent->parent->getProperties();
One possible answer is to use Singletons

18. Singleton Example
//h file class Singleton { public: static Singleton* Instance(); ~Singleton(); int getValue(); private: Singleton(); int m_value; static Singleton* sm_instance; };
//c++ file
Singleton* Singleton::sm_instance = NULL;
Singleton::Singleton() { }
Singleton::~Singleton() {
Singleton* Singleton::Instance() {
if (Singleton::sm_instance == NULL) {
Singleton::sm_insta nce = new Singleton();
return Singleton::sm_instance;
int Singleton::getValue() {
return m_value;
//main.cpp file int main (int argc, char** argv) { //blah blah blah Singleton* singletonObj = Singleton::Instance(); delete singletonObj; return 0; }

19. Programming Strategies?
What do you think is the best way to deal with the state machine and maintain state variables?
How to access local variables (that correspond to state variables)?
Efficiency considerations?
How do you think the programming with a state machine affects multi-threaded applications?

20. Multi-Threading and OpenGL
Thread A
Thread B
void drawRedDashedTriangle() { pushAttributes(); setColor (RED); setStyle (DASHED); drawLine (pt1+d, pt2+d); drawLine (pt2+d, pt3+d); drawLine (pt3+d, pt1+d); d++; popAttributes(); }
void drawBlueSolidTriangle() { pushAttributes(); setColor (BLUE); setStyle (SOLID); drawLine (pt4-p, pt5-p); drawLine (pt5-p, pt6-p); drawLine (pt6-p, pt4-p); p--; popAttributes(); }

21. Multi-Threading and OpenGL
Thread A
Thread B
void drawRedDashedTriangle() { mutex.lock(); pushAttributes(); setColor (RED); setStyle (DASHED); drawLine (pt1+d, pt2+d); drawLine (pt2+d, pt3+d); drawLine (pt3+d, pt1+d); d++; popAttributes(); mutex.unlock(); }
void drawBlueSolidTriangle() { mutex.lock(); pushAttributes(); setColor (BLUE); setStyle (SOLID); drawLine (pt4-p, pt5-p); drawLine (pt5-p, pt6-p); drawLine (pt6-p, pt4-p); p--; popAttributes(); mutex.unlock(); }

22. Questions?

23. Typical OpenGL Application

24. Example
Here we use GLUT, which is a basic GL window implementation that is on all platforms.
Pros: cross-platform, command line, easy to use
Cons: no GUI support (no buttons, menus, etc.)

25. Example OpenGL Application
int main( int argc, char** argv ) { glutInit( &argc, argv ); // Boilerplate initialization glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); glutInitWindowPosition( 50, 50 ); //upper left glutInitWindowSize( 640, 480 ); // width, height, in pixels glutCreateWindow( "OpenGL Example" ); // window title glViewport( /* lower left corner of the viewport */ 0, 0, /* width, height of the viewport */ 640, 480 ); //lower left
What’s going on here?

26. Example OpenGL Application
int main( int argc, char** argv ) { glutInit( &argc, argv ); // Boilerplate initialization glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
#define GLUT_RGB 0
#define GLUT_RGBA GLUT_RGB
#define GLUT_INDEX 1
#define GLUT_SINGLE 0
#define GLUT_DOUBLE 2
#define GLUT_ACCUM 4
#define GLUT_ALPHA 8
#define GLUT_DEPTH 16
#define GLUT_STENCIL 32
#if {GLUT_API_VERSION >= 2}
#define GLUT_MULTISAMPLE 128
#define GLUT_STEREO 256
#endif
#if {GLUT_API_VERSION >= 3}
#define GLUT_LUMINANCE 512
What is a Bit Mask?

27. Quick Word on Bit Masking…
Let’s say I have a bit string to store the current state of my variables: 1001
Making the state:
int myState = (var1 | var4)
Checking the state: If I want to ask if variable 1 is on:
if (myState & var1 > 0)
Lastly, on image-based bit masking…
*Note: the black pixels represent “transparent pixels”

28. Example OpenGL Application
int main( int argc, char** argv ) { glutInit( &argc, argv ); // Boilerplate initialization glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH ); glutInitWindowPosition( 50, 50 ); //upper left glutInitWindowSize( 640, 480 ); // width, height, in pixels glutCreateWindow( "OpenGL Example" ); // window title glViewport( /* lower left corner of the viewport */ 0, 0, /* width, height of the viewport */ 640, 480 ); //lower left
Careful!!

30. Example OpenGL Application
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }
Asks OpenGL to render with smooth (Gouraud) shading. Other option is GL_FLAT

31. Example OpenGL Application
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }
Asks OpenGL to render fill the polygons but only in the front-facing side
Options are GL_BACK, GL_FRONT_AND_BACK, and GL_POINT, GL_LINE, GL_FILL

32. Example OpenGL Application
void setupLighting() {
glEnable (GL_LIGHTING);
glEnable (GL_LIGHT0);
GLfloat whiteColor[] =
{0.25f, 0.25f, 0.25f, 1.0f};
glLightfv (GL_LIGHT0, GL_AMBIENT,
whiteColor);
//directional (diffuse) light
GLfloat whiteFull[] =
{1.0f, 1.0f, 1.0f, 1.0f};
GLfloat lightPos[] =
{-1.0f, 1.0f, 1.0f, 0.0f};
glLightfv(GL_LIGHT0, GL_DIFFUSE,
whiteFull);
glLightfv(GL_LIGHT0, GL_POSITION,
lightPos);
GLfloat grey[] =
{0.1f, 0.1f, 0.1f, 1.0f};
glMaterialfv(GL_FRONT, GL_DIFFUSE,
grey); //reflect 10% diffuse
glMaterialfv(GL_FRONT, GL_AMBIENT,
whiteFull);}//reflect full ambient
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }

33. Example OpenGL Application
void setupCamera(int w, int h) {
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
//left, right, bottom, top
gluOrtho(-1, 1, -1, 1);
//same as: (adds near, far)
//glOrtho(-1,1,-1,1,-1,1);
//or perspective transform
//gluPerspective(
// 45, //y-axis field of view
// ((float)w/(float)h),
// ratio of FOV(x) to FOV(y)
// 0.02,
//distance to near clip plane
// 1000
//distance to far clip plane
// );
glMatrixMode (GL_MODELVIEW); }
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }

34. Example OpenGL Application
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }
void registerCallbacks() {
glutReshapeFunc (myReshape);
glutKeyboardFunc (myKeyboard);
glutMouseFunc (myMouseClick);
glutMotionFunc (myMouseMove);
glutDisplayFunc (myDisplay);
glutIdleFunc (myIdle); }

35. Example OpenGL Application
void myReshape(GLint width, GLint height) { //called when the window is resized glViewport(0, 0, width, height); setupCamera(width, height); } void myKeyboard (unsigned car key, int x, int y) { //called on keyboard event switch (key) { case ‘a’: someGlobalVariable = 1; :
void registerCallbacks() {
glutReshapeFunc (myReshape);
glutKeyboardFunc (myKeyboard);
glutMouseFunc (myMouseClick);
glutMotionFunc (myMouseMove);
glutDisplayFunc (myDisplay);
glutIdleFunc (myIdle); }

36. Example OpenGL Application
void myMouseClick(int button, int state, int x, int y) { //called when a mouse click occurs if (button == GLUT_LEFT_BUTTON) { if (state == GLUT_DOWN) { globalVariableMouseDown = true; } else { globalVariableMouseDown = false; void myMouseMove (int x, int y) { //called when a mouse move occurs if (globalVariableMouseDown==true) { //dragging occurs
void registerCallbacks() {
glutReshapeFunc (myReshape);
glutKeyboardFunc (myKeyboard);
glutMouseFunc (myMouseClick);
glutMotionFunc (myMouseMove);
glutDisplayFunc (myDisplay);
glutIdleFunc (myIdle); }

37. Example OpenGL Application
void display(void) { //called when the window needs to paint itself glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); drawMyStuff(); glutSwapBuffers(); numberOfFrames++; } void myIdle (void) { //called ALL THE TIME!! DWORD time_now = GetTickCount(); float diff = (float)(time_now-last_check_time)/1000.0; if (diff > 1.0) { float frameRate = numberOfFrames / (float)diff; numberOfFrames = 0; last_check_time = time_now; glutPostRedisplay();
void registerCallbacks() {
glutReshapeFunc (myReshape);
glutKeyboardFunc (myKeyboard);
glutMouseFunc (myMouseClick);
glutMotionFunc (myMouseMove);
glutDisplayFunc (myDisplay);
glutIdleFunc (myIdle); }

38. Example OpenGL Application
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop(); }
No turning back at this point, we enter the infinite loop!

39. Typical OpenGL Application

40. Questions?

41. Drawing Primitives
void drawMyStuff(void) { glBegin (...); //glColor3f(1.0f, 1.0f, 1.0f); //glNormal3f(0.0f, 0.0f, 1.0f); glVertex3f(1.0f, 1.0f, 1.0f); glVertex3f(1.0f, 2.0f, 1.0f); : glEnd(); }

42. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

43. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

44. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

45. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

46. void glFrontFace (GLenum mode) mode can be either GL_CW or GL_CCW
Ordering of Vertices
void glFrontFace (GLenum  mode)
mode can be either GL_CW or GL_CCW
GL_CCW is the default

47. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

48. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

49. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

50. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON

51. OpenGL Primitives
GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON
1. Must be convex
2. Cannot intersect

52. Color Blending
glColor3f (1.0, 0.0f, 0.0f); glBegin(GL_TRIANGLES); glVertex3f(-1.0f, -0.5f, -4.0f); // A glVertex3f( 1.0f, -0.5f, -4.0f); // B glVertex3f( 0.0f, 0.5f, -4.0f); // C glEnd();

53. Color Blending
glBegin(GL_TRIANGLES); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0f, -0.5f, -4.0f); // A glColor3f(0.0f, 1.0f, 0.0f); glVertex3f( 1.0f, -0.5f, -4.0f); // B glColor3f(0.0f, 0.0f, 1.0f); glVertex3f( 0.0f, 0.5f, -4.0f); // C glEnd();

54. GL Shade Model
glShadeModel( GL_FLAT ); glBegin(GL_TRIANGLES); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0f, -0.5f, -4.0f); // A glColor3f(0.0f, 1.0f, 0.0f); glVertex3f( 1.0f, -0.5f, -4.0f); // B glColor3f(0.0f, 0.0f, 1.0f); glVertex3f( 0.0f, 0.5f, -4.0f); // C glEnd();

55. GL Normal
The direction where the face of the triangle points towards
Unit vector
Or call ( glEnable(GL_NORMALIZE); )

56. GL Normal
These two have the same number of quads…
What is the difference?

57. GL Normal

58. GL Normal glNormal3f(nx, ny, nz); glBegin(GL_QUADS);
glVertex3f(x1, y1, z1);
glVertex3f(x2, y2, z2);
glVertex3f(x3, y3, z3);
glVertex3f(x4, y4, z4);
glEnd();

59. GL Normal glBegin(GL_QUADS); glNormal3f(nx1, ny1, nz1);
glVertex3f(x1, y1, z1);
glNormal3f(nx2, ny2, nz2);
glVertex3f(x2, y2, z2);
glNormal3f(nx3, ny3, nz3);
glVertex3f(x3, y3, z3);
glNormal3f(nx4, ny4, nz4);
glVertex3f(x4, y4, z4);
glEnd();

60. Data transport from CPU to GPU
Note on Display List
Data transport from CPU to GPU
Consider the example before…
At 60fps, there’s a lot redundancy
How to make it more efficient?

61. Data transport from CPU to GPU
Note on Display List
Data transport from CPU to GPU
Consider the example before…
How to make it more efficient?
Push things onto the GPU memory…
Display List
Vertex Buffer Objects (VBO)
etc.
Cost of readability (e.g.,

62. Questions?

63. Don’t Forget!!!!
For the Windows users, download Visual Studio from Tufts UIT (which is free)
Two ways to do this:
If you have a CS unix account, go to:
click on “userguide”, then login.
Click on “Access to Microsoft Software Downloads (msdnaa)” under “Software”
If you don’t have a CS account, go to:
click on “students” (on top)
Register (if necessary)