1. Programming With OpenGL
A Technical Overview of The OpenGL Graphics API
Programming With OpenGL
Computer Graphics

2. Graphics API OpenGL(All Platform) DirectX(Windows) -DirectDraw
-DirectSound
-DirectPlay
-DirectInput
-DirectSetup
OpenGL(All Platform)
DirectX(Windows)

3. Programming With OpenGL
An Introduction
OpenGL, the standard software interface for graphics hardware, allows programmers to create interactive 2D and 3D graphics applications on a variety of systems. With OpenGL you can create high-quality color images. OpenGL makes it easy to build geometric models, change the viewing position, control the color and lighting of geometric primitives, and manipulate pixel and texture map images. This course will cover an immediately applicable subset of OpenGL, so that you can write a simple graphics program.
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4. OpenGL Advantages OpenGL is the most logical extension of
Programming With OpenGL
OpenGL Advantages
Standard & Portability - Open
OpenGL is the most logical extension of
brilliant API called GL
Supported through a larger number of vendors
1992, SGI
SGI, IBM, DEC, Intel, Microsoft,
Vendor and hardware independent
Better integration into the windowing system
Win95, Win98, WinNT, Win2000,WinXP
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5. Objectives Understand the order of operations, and the major libraries
Programming With OpenGL
Objectives
Become familiar with the capabilities of OpenGL
Understand the order of operations, and the
major libraries
Know how to use viewing, lighting, shading,
and hidden surface removal functionality
Know how to draw images with OpenGL and
process event-driven input
See how code is written and compiled
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6. Programming With OpenGL
What is OpenGL?
A low-level graphics modeling and rendering library (includes more than 100 functions)
State machine
A layer of abstraction between graphics hardware and an application program
Hardware, Window System and Operating System independent
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7. Where is in the Graphics System
Programming With OpenGL
Where is in the Graphics System
Developing &
Application
OpenInventor, SoftImage 3D
OpenGL
Window System
X-Windows, MS Windows …
Operating System
UNIX, MS Windows, OS/2...
Graphics Hardware
SGI-XZ, SGI-Extreme, AGC-3D..
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8. What OpenGL Can Do For You
Programming With OpenGL
What OpenGL Can Do For You
Wireframe Models, Viewing, Transformation
Antialiasing
Flat And Smooth Shading
Shadows
Texture Mapping
Motion Blur
Haze and Fog, Depth -Of -Field Effect
Evaluator Function: 1D & 2D Bezier Curves, NURBS ...
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9. Graphics Functions Primitive functions Attribute functions
Programming With OpenGL
Graphics Functions
Primitive functions
Attribute functions
Viewing functions
Transformation functions
Input functions / control functions
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10. Overview of OpenGL Components
Programming With OpenGL
Overview of OpenGL Components
OpenGL Library - gl
OpenGL Utilities - glu
OpenGL Extension to X Windows - glx
OpenGL Programming Guide Auxiliary Library - aux
Windows Graphics Library - wgl
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11. OpenGL Library GL Powerful But Primitive Set Of Rendering Commands
Programming With OpenGL
OpenGL Library GL
Powerful But Primitive Set Of Rendering Commands
All high level drawing is done in terms of these commands
You can write your own toolkit based on these functions
The GL Library Includes
Functions supporting drawing primitives
Lines, Points, Circles, Polygons, Characters, ...
Clipping, Viewing, Projections, Transformation
Shading, Lighting
Direct colors
3D rendering functions such as
Antialiasing, Multi buffering, Texture, ...
Pixels manipulation (read, write, copy)
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12. OpenGL Utility Library GLU
Programming With OpenGL
OpenGL Utility Library GLU
Utility library is a set of commonly used graphics routines
built on top of OpenGL
Uses lower level OpenGL commands for
Setting up matrixes for viewing and projection
Performing polygon tessellation
- concave polygons, polygons with holes, self- intersecting polygons, ..
Rendering surfaces (spheres, cylinders, disks, ..)
Mipmapping
NURBS (Non-Uniform Rational B-Spline) curves
Error handling
This library is part of the OpenGL implementation
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13. OpenGL Auxiliary Library
Programming With OpenGL
OpenGL Auxiliary Library
This is a simple, platform-dependent library
Makes programming examples simpler & more
complete
Managing windows
Handling input events
Drawing classic 3-D objects
Managing a background process
Running a program
Do not use them in a production application
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14. OpenGL Command Syntax OpenGL commands use : OpenGL define constants
Programming With OpenGL
OpenGL Command Syntax
OpenGL commands use :
the prefix gl
initial capital letters for each word making up the command name
OpenGL define constants
begin with GL
use all capital letters
use underscore to separate words
OpenGL uses command extensions for clarification
whenever the same command exists to use different arguments
Examples :
glClearColor()
GL_COLOR_BUFFER_BIT
glColor3fv()
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15. OpenGL Command Syntax  glVertex3fv
Programming With OpenGL
OpenGL Command Syntax
 glVertex3fv
v indicates vector format, if present
data type: f float
d double float
s signed short integer
i signed integer
number of components (2, 3, or 4)
Other data types in OpenGL commands
- b character
- ub unsigned character
- us unsigned short integer
- ui unsinged integer
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16. Programming With OpenGL
Drawing Geometry
Vertices can define a variety of geometric objects, and different numbers of vertices are required depending on the object.
We can group as many vertices as desired, using the functions glBegin() and glEnd()
Types of primitives glBegin (GLenum primitiveType)
Example:
glBegin (GL_POLYGON);
glVertex3f(-. 5f, -. 5f, -. 5f);
glVertex3f(. 5f, -. 5f, -. 5f);
glVertex3f(-. 5f, .5f, -. 5f);
glVertex3f(. 5f, .5f, -. 5f);
glEnd();
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17. Programming With OpenGL
Primitive Types
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18. Attributes primitive is to be rendered graphics system
Programming With OpenGL
Attributes
An attribute is any property that determines how a geometric
primitive is to be rendered
The present values of attribute are part of the state of the
graphics system
Each geometric type has a set of attributes
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19. Attributes Vertex attributes: glPointSize() point size
Programming With OpenGL
Attributes
Vertex attributes:
glPointSize() point size
glColor*()/ glIndex*() current vertex color
glNormal*() current vertex normal (lighting)
glMaterial*() current material property (lighting)
glTexCoord*() current texture coordinate
glEdgeFlag*() edge status (surface primitives)
RGB colors:
glColor3f(1.0,0.0,0.0)
glClearColor(1.0,1.0,1.0,1.0)
Indexed color:
glIndexi(element)
Alpha channel
- opacity or transparency
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20. Drawing Geometry Example: Drawing a green, flat triangle strip:
Programming With OpenGL
Drawing Geometry
Example: Drawing a green, flat triangle strip:
glBegin (GL_ TRIANGLE_ STRIP);
glColor3f( 0. f, 1. f, 0. f);
glNormal3f( 0. f, 0. f, 1. f);
glVertex3f(-. 5f, -. 5f, -. 5f);
glVertex3f(. 5f, -. 5f, -. 5f);
glVertex3f(-. 5f, .5f, -. 5f);
glVertex3f(. 5f, .5f, -. 5f);
glEnd();
glBegin - glEnd paradigm allows great flexibility in describing primitives.
Any combination of color, normal, texture, material etc. information can be bound with any given vertex.
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21. OpenGL The Statemachine
Programming With OpenGL
OpenGL The Statemachine
OpenGL knows about various different states or modes
These states remain in effect until you change them
Examples of states variables are:
the current color
current viewing and transformation matrix
line and polygon stippling patterns
polygon drawing modes
shading modes
pixel packing conventions
position and characteristics of light sources
material properties
Each state variable has a default value
You can query the current variable value
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22. States glEnable (GLenum capability) glDisable (GLenum capability)
Programming With OpenGL
States
glEnable (GLenum capability)
glDisable (GLenum capability)
GLboolean glIsEnabled (GLenum cap)
- turn on and off OpenGL states
- capability can be one of (partial list):
GL_ BLEND (alpha blending)
GL_ DEPTH_ TEST (depth buffer)
GL_ FOG
GL_ LIGHTING
GL_ LINE_ SMOOTH (line antialiasing)
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23. Structure of a Typical Program
Programming With OpenGL
Structure of a Typical Program
main:
create window
initialize GL states (e. g., viewing, color, lighting)
initialize display lists
check for events (and process them)
if window event (window moved, exposed, etc.)
- modify viewport, if needed
- redraw
else if mouse or keyboard
- do something, e. g., change states & redraw
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24. Initialization void auxInitWindow(Glbyte *titleString)
Programming With OpenGL
Initialization
void auxInitWindow(Glbyte *titleString)
- Win32 API: CreateWindow(…)
void auxInitDisplayMode(Glbitfield mask)
Mask: AUX_RGBA or AUX_INDEX
AUX_SINGLE or AUX_DOUBLE
AUX_DEPTH
AUX_STENCIL
AUX_ACCUM
void auxInitPosition(Glint x,Glint y,
Glsizei width,Glsizei height)
- Win32 API: MoveWindow(…)
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25. Control Functions (GLsizei,Glsizei)) void(*function)(AUX_EVENTREC*))
Programming With OpenGL
Control Functions
void auxMainLoop(void(*displayFunc)void))
-Windows message: WM_PAINT
void auxReshapeFunc(void(*function)
(GLsizei,Glsizei))
-Windows message: WM_SIZE
void auxMouseFunc(Glint button,Glint mode,
void(*function)(AUX_EVENTREC*))
- Windows Message: WM_MOUSEDOWN
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26. Redraw redraw: clear screen (to background color)
Programming With OpenGL
Redraw
redraw:
clear screen (to background color)
change state( s), if needed
render some graphics
change more states
render some more graphics
....
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27. Homework: The Sierpinski Gasket
Programming With OpenGL
Homework: The Sierpinski Gasket
1. Pick an initial point at random inside the triangle.
2. Select one of the three vertices at random.
3. Find the point halfway between the initial point and the randomly selected vertex.
4. Display this new point by putting some sort of marker, such as a small circle, at its location.
5. Replace the initial point with this new point.
6. Return to step 2. V2 P0 P1 P2 V1 V3
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