OpenGL Course Notes

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OpenGL Course Notes Chapter 1 Introduction
Jim Mims
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Table of Contents

• ? Origin and Purpose
• ? C Essentials
• ? Some Definitions
• ? Required Software
• ? Include Files
• ? Managing Windows Windows Procedures Vs GLUT
  Functions
• ? GLUT Windows Management Functions
• ? Handling Input Events
• ? Some Built-In 3D Objects
• ? Example Code

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OpenGL Origin and Purpose
The OpenGL API (Application Programming
Interface) began as an initiative by Silicon
Graphics to create a single, vendor-independent
API for the development of 2D and 3D graphics
applications. Prior to the introduction of
OpenGL, many hardware vendors had different
graphics libraries. This situation made it
expensive for software developers to support
versions of their applications on multiple
hardware platforms, and it made porting of
applications from one hardware platform to
another very time-consuming and difficult. 
Silicon Graphics saw the lack of a standard
graphics API as an inhibitor to the growth of the
3D marketplace and decided to lead an industry
group in creating such a standard.  
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OpenGL Origin and Purpose
The result of this work was the OpenGL API 
library. The OpenGL API began as a specification,
then  a sample implementation was produced that
hardware vendors could use to develop OpenGL
drivers for their hardware. The sample
implementation has been released under an open
source license.   Modifications to the OpenGL API
are made through the OpenGL Architecture Review
Board, an industry group that contains founding,
permanent, and auxiliary members.    
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OpenGL Origin and Purpose
The OpenGL specification is overseen by the
OpenGL Architecture Review Board (ARB). The
OpenGL Architecture Review Board (ARB) is an
industry consortium that currently governs the
OpenGL specification. It was formed in 1992, and
defines the conformance tests, approves the
OpenGL specification and advances the standard.
In July 2006, it was announced that the ARB
voted to transfer control of the OpenGL
specification to the Khronos Group.
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OpenGL Origin and Purpose
The Khronos Group is a member-funded industry
consortium focused on the creation of open
standard, royalty-free APIs to enable the
authoring and accelerated playback of dynamic
media on a wide variety of platforms and devices.
All Khronos members are able to contribute to
the development of Khronos API specifications,
are empowered to vote at various stages before
public deployment, and are able to accelerate the
delivery of their cutting-edge 3D platforms and
applications through early access to
specification drafts and conformance tests.
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C Essentials
Functions Groupings of code that accomplish a
task. Enclosed in braces Main Function All
programs must have one Enclosed in braces Last
line is return 0 Semicolons Used to terminate a
line of code Importing Libraries include ltname
of librarygt if in standard C library include
name of library if not in standard C
library            
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C Essentials
Some Data Types  int, float, double, char,
string Some Operators gt, lt, , , !     
Loops For (int i 0 ilt10i) //code
goes here           Calling a Function Use
the name of the function         VB 6 ByRef or
ByVal          Comments // or //
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Some Definitions
Geometric Primitives Points, lines, and
polygons Models Objects constructed from
geometric primitives Rendering Process by which
computer generates images (things on the screen)
from models Bit A 0 or a 1 Bitplane Area in
memory that holds one bit of information for
every pixel on the screen (how green, for
example) Framebuffer Contains the bitplanes
all the graphics information the graphics display
needs to control the color and intensity of all
the pixels on the screen
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Some Definitions
Rendering Pipeline Series of processing stages
summarized next Rendering Pipeline Display
Lists Data structure for storing all data
(geometric primitives or pixels) for subsequent
use. The alternative is to process the data
immediately (immediate mode) Rendering Pipeline
Evaluators All geometric primitives described by
vertices. Surfaces and curves described by
control points and basis functions. Evaluators
derive vertices from the surface and curve
representations. Rendering Pipeline Primitive
Assembly Includes cleanup operations such things
as clipping. Rendering Pipeline Pixel
Operations Operations on pixels geometric data
takes a different route.
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Some Definitions
Rendering Pipeline Texture Assembly Applying
textures onto geometric objects to make them look
more realistic. Rendering Pipeline
Rasterization The conversion of both geometric
and pixel data into fragments. Each fragment
square corresponds to a pixel in the framebuffer.
Color and depth values are assigned for each
square. Rendering Pipeline Fragment
Operations Series of operations that are
performed before the values are stored in the
framebuffer. Fragments may be altered or removed.
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Required Software
The location of the following software is system
dependent. For Windows, the following files
should be in a directory similar to the
following Program Files\Microsoft Visual
Studio\VC\include\gl gl.h Primary OpenGL header
file. Contains prototypes for various
functions glu.h Header file for the OPenGL
Utility library glut.h Header file for OpenGL
Graphic Library Utility Toolkit - used to manage
Windows. Ensures that gl.h and glu.h are included
automatically - including them with separate code
is redundant.  
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Required Software
For Windows, the following files should be in a
directory similar to the following Program
Files\Microsoft Visual Studio\VC\lib
Opengl32.lib Library containing bindings to
OpenGL functions. glu32.lib Library containing
bindings to OpenGL Utility Library
functions Glut32.lib Library contining bindings
to GLUT Library functions
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Required Software
For Windows, the following files should be in a
directory similar to the following
Windows\System32 opengl32.dll Dynamic link
library containing OpenGL function
implementations and hooks into video hardware
drivers. glu32.dll Dynamic link library
containing OpenGL Utility Library function
implementations.  
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Include Files
include ltGL/gl.hgt include ltGL/glu.hgt include
is a C preprocessor directive. It tells the
compiler to insert the file included in lt gt The
ltgt indicates that the files are in the standard
library directory for C The GL is a sub
directory in the include directory created when
you install Windows.
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Managing Windows Windows Vs GLUT Functions
There are 2 options using Windows procedures
(not intuitive) or using GLUT functions. This
course emphasizes the latter. To use Windows
procedures you open C and select File, New,
Win32 Application. You must include
ltwindows.hgt GLUT stands for OpenGL Utility
Toolkit it is used to perform windows
activities controlling the window. To use GLUT
functions, you open C and select File, New,
Win32 Console Application. You must include
ltglut.hgt. Glut.h ensure that both gl.h and glu.h
are included.
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Windows Management Functions
glutInit() Initializes GLUT should be called
before any other GLUT function. glutInitDisplayMo
de(int mode) Specifies whether to use an RGBA or
color-index color model and to set some other
items. glutInitWindowPosition(int x, int
y) Specifies the screen location for the
upper-left corner of the window. glutWindowSize(i
nt width, int size) Specifies the size, in
pixels, of the window. glutCreateWindow() Creates
a window glutMainLoop() Displays the window
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Handling Input Events
glutReshapeFunc(int w, int h) Indicates what
action should be taken when the window is
resized. glutKeyboardFunc(char key, int x, int
y) glutMouseFunc(int button, int state, int x,
int y) Allow you to link a keyboard key or a
mouse button with a routine that is invokes when
the key or mouse button is pressed or
released glutMotionFunc(int x, int y) Regisers a
routine call back when the mouse is moved while a
mouse button is also pressed.
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Some Built-In 3D Objects
glutSolidSphere(double radius, int slices, int
stacks) glutWireSphere(double radius, int slices,
int stacks) Renders a sphere centered at the
modeling coordinates origin of the specified
radius. The sphere is subdivided around the Z
axis into slices and along the Z axis into
stacks. radius is the radius of the
sphere slices is  the number of subdivisions
around the Z axis stacks is the number of
subdivisions along the Z axis   glutSolidCube
(double size) glutWireCube(double size) Render a
solid or wireframe. The cube is centered at the
modeling coordinates origin with sides of length
size.    
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Some Built-In 3D Objects
glutSolidCone(base, height, slices,
stacks) glutWireCone(base, height, slices,
stacks)   Render a solid or wireframe cone
respectively oriented along the z axis. The base
of the cone is placed at z0, and the top at
zheight. The cone is subdivided around the z 
axis into slices, and along the z axis into
stacks.   base is the radius of the base of the
cone height is the height of the cone slices is
the number of subdivisions around the Z
axis stacks is the number of subdivisions along
the Z axis    
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Some Built-In 3D Objects
glutSolidTorus(double innerRadius, double
outerRadius, int nsides, int rings) glutWireTorus
(double innerRadius, double outerRadius, int
nsides, int rings)   Render a solid or wireframe
torus (doughnut) respectively centered at the
modeling coordinates origin whose axis is aligned
with the Z axis.   innerRadius is the inner
radius of the torous outerRadius is the outer
radius of the torus nsides is teh number of sides
for each radial section rings is the number of
radial divisions for the torus    
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Some Built-In 3D Objects
glutSolidTeapot(double size) glutWireTEapot(double
size)   Render a solid or wireframe teapot
respectively. Both surface normals and texture
coordinates for the teapot are generated. Size
is the relative size of the teapot glutSolidTetra
hedron() glutWireTetrahedron()   Render a solid
or wireframe tetrahedron respectively centered at
the modeling coordinates origin with a radius
square root of 3.          
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Many Teapots
       
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Clipped Wireframe Sphere
       
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Example Code
include ltGL/glut.hgt include ltstdlib.hgt void
display(void) //clear all pixels glClear
(GL_COLOR_BUFFER_BIT) //draw white polygon
(rectangle) with indicated corners 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()
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Example Code
//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)
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Example Code
/
Declare
initial window size, position, and display mode
(single buffer, 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
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Example Code Output