1. Lecture 03 Overview of Computer Graphics Programming
CSC4820/6820 Computer Graphics Algorithms Ying Zhu Georgia State University
Lecture 03
Overview of Computer Graphics Programming

2. Creating 3D Graphics Content
Different ways to create graphics content
If you want to create non-interactive 3D animations
Use graphics modeling/animation tools: 3DS Max, Maya, Blender, etc.
If you want to create interactive 3D applications (game, training & simulation program)
A combination of both modeling/animation tools and programming
C/CPP + scene graph + OpenGL/D3D + Shader

3. Graphics Libraries (APIs)
3D graphics applications are built on top of graphics libraries
A collection of graphics routines that an application program can call
The APIs hide the underlying complexity of graphics hardware and/or lower level APIs
Large scale graphics applications are usually built on top of high level graphics APIs

4. Graphics Libraries (APIs)
High level APIs are implemented on top of low level graphics APIs
Low level APIs control graphics hardware through graphics drivers
Between low level graphics APIs and graphics drivers there are shader libraries

5. High Level Graphics APIs
Also known as Scene Graph APIs
Non-real-time oriented APIs
Java3D
VRML & X3D
Open Inventor
Renderman

6. High Level Graphics APIs
Real-time oriented APIs
3D graphics and game engines
Torque Game Engine
OGRE
OpenGL Performer
Open Scene Graph
OpenSG
Many proprietary high level APIs

7. Game Engines Game engine
Graphics API designed specifically for game development
Contains all non-content related functions/elements

8. Game Engine Game Architecture Gameplay Game engine Tools & Editor
Graphics Hardware

9. Modern Game Engine Features
Scene management
Culling,
Rendering
Bump mapping
Shadow
Collision
Decals AI
Particle systems, etc.
Shader management

10. Game Engines There are hundreds of game engines
Most popular game engines
Torque Game Engine (commercial)
OGRE (open source)
For a comprehensive list, check out

11. Torque Game Engine
A very popular game engine with multi-player network code, indoor/outdoor rendering engines, skeletal animation, drag and drop GUI creation, a built in world editor, and a C- like scripting language.

12. OGRE Object-oriented Graphics Rendering Engine
A scene-oriented, flexible 3D engine written in C++ designed to make it easier and more intuitive for developers to produce games and demos using 3D hardware.

13. OGRE example

14. OGRE example

15. Java3D High level object-oriented scene graph API
Platform independent, implemented on top of Direct3D or OpenGL
Try to meet a wide variety of application requirements
Real-time performance
Object modeling
Input devices support
Stereoscopic vision

16. JOGL Java OpenGL (JOGL) https://jogl.dev.java.net/
A wrapper library that allows OpenGL to be used in the Java programming language

17. VRML & X3D VRML = Virtual Reality Modeling Language X3D
HTML like language for describing 3D shapes and interaction
X3D
Next generation open standard for 3D on the web
Officially replaced VRML in July 2004
X3D supports XML for tight integration with Web technologies and tools

18. OpenGL Performer http://www.sgi.com/products/software/perfor mer/
A graphics API developed by SGI for real-time visual simulation and other performance oriented applications
Implemented on top of OpenGL, with performance as the first priority
mer/
Performer has great influence on other real-time graphics APIs
E.g. Open Scene Graph (

19. Why so many scene graph APIs & game engines?
Different target applications
Real-time vs. non-real-time applications
Application specific optimizations
Application specific entities
E.g. different game genres require different game engines

20. Why so many scene graph APIs & game engines?
Language and platform considerations
Platform specific optimizations
Open source vs. proprietary APIs
Integration of new technologies
Not necessarily a good thing
Lack of documents & sample code

21. Low Level Graphics APIs
Directly handles 3D rendering
Very efficient implementation
Only two major low level 3D graphics APIs
OpenGL
Direct3D (part of DirectX)
Comparison of Direct3D and OpenGL
t3D_and_OpenGL

22. Direct3D Part of Microsoft’s DirectX libraries
Including Direct3D, DirectInput, DirectSound, etc.
Designed for real-time graphics applications
Computer game
Home entertainment
Primary choice for game development
Latest version is DirectX 10
Only supported on MS Windows platform

23. Using Direct3D Benefits Drawbacks
Supported by most of the graphics hardware
Better game support
Better integration with other MS stuff (e.g. .Net)
Maintained by one single company
Quick to add new features to Direct3D
Drawbacks
Somewhat more difficult to learn than OpenGL
Windows only

24. OpenGL Platform independent graphics API Window system independent
MS Windows, Linux, IRIX, Solaris, Mac, etc.
Window system independent
MS Windows, X Window
Maintained by KHRONOS group (an industry consortium)
Members include 3Dlabs, AMD, NVIDIA, Intel, Google, etc.
Current specification: OpenGL 3.0

25. Using OpenGL Benefits Drawbacks http://www.opengl.org/ Open standard
Supported by all the graphics cards
Supported by all the platforms
Lots of books, tutorials, and samples available
Most of the mainstream 3D graphics textbooks use OpenGL
Drawbacks
Historically, OpenGL is often slow to add new features
Users are often forced to use OpenGL extensions

26. OpenGL Extension
OpenGL extensions provide new rendering features above and beyond the features specified in the official OpenGL standard
To keep the OpenGL API current with the latest innovations in graphics hardware and rendering algorithms
Different kind of extensions:
Extensions ratified by the ARB: GL_ARB_multitexture();
Extensions agreed on by multiple vendors: GL_EXT_abgr();
Vendor specific extensions: GL_NV_register_combiners();

27. OpenGL Extension
To find out what OpenGL extensions your graphics card supports, download and install Glview utility (OpenGL extension viewer)

28. OpenGL Related APIs GLU (OpenGL Utility Library)
Mostly modeling related functions: NURBS, tessellators, etc.
Part of OpenGL
GLX: connecting OpenGL with X Window
WGL: connecting OpenGL with MS Windows

29. OpenGL Related APIs GLUT (OpenGL Utility Toolkit)
implements a simple windowing application programming interface (API) for OpenGL
makes it easier to learn OpenGL programming
designed for constructing small to medium sized OpenGL programs
We will use GLUT in this class
Binary files:
Reference manual: 3.html

30. GPU and Shader
Graphics Processing Units are the microprocessors on the newer graphics cards
Nvidia, AMD, and Intel are the main GPU vendors
You can write programs that runs on GPU using a special programming language
These programs are called shaders
The programming languages are called shading languages

31. Shader Programming Why use shaders? Faster and more flexible
To implement features that are not available on OpenGL or Direct3D
Take advantage of GPU, which is is optimized for graphics applications
Faster and more flexible
High level shading languages
Cg, HLSL, OpenGL SL, Sh
Load, compile, and run shader programs from OpenGL or DirectX programs

32. OpenGL Files
OpenGL files comes with MS Windows and/or Visual Studio installation
Header files
gl.h, glu.h
Glut.h (needs to be downloaded)
Static libraries
Opengl32.lib, glu32.lib
glut32.lib (needs to be downloaded)
DLLs
C:\windows\system32
Opengl32.dll, glu32.dll
glut32.dll (needs to be downloaded)

33. How to compile OpenGL/GLUT programs?
ll04-22C151/howto/winGLUT.html
ACTIVE_COMPUTER_GRAPHICS/FOURTH _EDITION/vc

34. Sample OpenGL programs
Examples from “OpenGL Programming Guide”
edbook/
OpenGL code samples:
Simple code samples: imple/

35. A Simple OpenGL Program (1)
#include <GL/glut.h>
void display(void) {
/* clear all pixels */
glClear (GL_COLOR_BUFFER_BIT);
/* draw white polygon (rectangle) with corners at
* (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0) */
glColor3f (1.0, 1.0, 1.0);
glBegin(GL_POLYGON);
glVertex3f (0.25, 0.25, 0.0);
glVertex3f (0.75, 0.25, 0.0);
glVertex3f (0.75, 0.75, 0.0);
glVertex3f (0.25, 0.75, 0.0);
glEnd();

36. A Simple OpenGL Program (2)
/* start processing buffered OpenGL routines */
glFlush (); }
void init (void) {
/* select clearing color */
glClearColor (0.0, 0.0, 0.0, 0.0);
/* initialize viewing values */
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);

37. A Simple OpenGL Program (3)
/* Declare initial window size, position, and display mode (single
buffer and RGBA). Open window with "hello" in its title bar. Call
initialization routines. Register callback function to display graphics.
Enter main loop and process events. */
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (250, 250);
glutInitWindowPosition (100, 100);
glutCreateWindow ("hello");
init ();
glutDisplayFunc(display);
glutMainLoop();
return 0; /* ANSI C requires main to return int. */ }

38. OpenGL Functions Overview (1)
Primitives: object creation
glBegin(), glEnd(); A glBegin()-glEnd() pair encloses an object definition. OpenGL functions called between glBegin() and glEnd() define the object
glVertex*(), glColor*(), glNormal*(), glMaterial*(), glCallList(), glCallLists(), glRect*(), gluSphere(), gluCylinder()
Attributes
glClearColor() and glClear() specify the color to be used when color buffers are cleared and to actually clear the buffer, respectively.
Attributes (all are modal) control how primitives are displayed: glPolygonMode(), glPointSize(), glLineStipple(), glLineWidth()

39. Overview of OpenGL Functions (2)
Display lists
glNewList(), glEndList(), glGenLists(), glListBase()
Display lists are collections of graphics functions. You create them, name them, and "execute" them.
You define objects in between glNewList() and glEndList().
Modeling transformations
glScale*(), glTranslate*(), glRotate*()
Before invoking any matrix manipulating function, you normally call glLoadIdentity().
Remember that glRotate() rotates about the origin so in order to rotate an object you usually must make sure that it is positioned at the origin.

40. OpenGL Functions Overview (3)
Viewing
gluLookAt()
The viewing transformation must precede modelling transformations in the code: you must first position the camera, then the objects.
Projection
gluOrtho2D(), glOrtho(), gluPerspective(), glViewport()
Call glMatrixMode( GL_PROJECTION) before you change projection parameters with any of the three functions above, then call glMatrixMode( GL_MODELVIEW). When the projection has been applied (whether simple discarding of z or a perspective division) we obtain normalized device coordinates. Finally these are mapped to (a portion of) the screen window. This mapping is specified with

41. OpenGL Functions Overview (4)
States
glEnable(), glDisable()
Almost everyting in OpenGL is modal, i.e. settings remain in effect until changed (this is true, not only of state variables we set with glEnable(), but also of normals, material properties, and colours).
Realism; light and shading
glLight*(), glLightModel*(), glMaterial*(), glShadeModel()
You must enable (with glEnable()) both lighting and the light sources you want to use.

42. OpenGL Functions Overview (5)
Hierarchical Models
glPushAttrib(), glPopAttrib(), glPushMatrix(), glPopMatrix()
In order to build hierarchical models we need ways of storing and restoring attributes and matrices. Display lists often start by pushing and ends by popping.
2D Texture & pixels
glTexImage2D(), glBindTexture(), glTexCoord2*(), glRasterPos*(), glBitmap(), glDrawPixels()
Texturing must be enabled explicitly.

43. GLUT Functions Overview (1)
Input and other callback functions
OpenGL programs execute in event mode, i.e. loops forever while awaiting user input. We write callback functions to be invoked as a result of user interaction. GLUT automatically calls the functions if we have registered them.
glutDisplayFunc(), glutMouseFunc(), glutMotionFunc(), glutReshapeFunc(), glutKeyboardFunc(), glutIdleFunc(), glutPostRedisplay()

44. GLUT Functions Overview (2)
Control Functions
Control functions are functions that interface with the windowing system. You (usually) call them from your main() function.
glutInit(), glutInitDisplayMode(), glutInitWindowSize(), glutCreateWindow(), glutMainLoop()

45. How to learn OpenGL? Read OpenGL Programming Guide
Read sample programs!
There are tons of OpenGL programs online:
Read tutorials
Write programs

46. How to learn OpenGL? Bookmark the OpenGL manual pages
You need this more than anything else
Bookmark the GLUT manual page
ec3/spec3.html
If you are really serious about learning OpenGL, read OpenGL specification

47. Other OpenGL Resources
OpenGL tutor
Tutorial programs that demonstrate basic OpenGL functionality by allowing the user to modify the parameters of a function and see the effect on the scene
OpenGL FAQ & Troubleshooting Guide
A good OpenGL tutorial

48. Readings
“Red Book”: Chapter 1 and 2

49. Next lecture
3D graphics pipeline