Today …
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The rendering pipeline in detail
What is OpenGL
First OpenGL program
Details about modeling
Basic Rendering Pipeline
Modeling
Transform
ation
(OS ->
WS)
Viewing
Transfor
mation
(WS ->
CS)
Visibility
Culling
Illuminat
ion
Project
ion
Rasteriz
ation
&
Clipping
&
Display
L
Database of 3D models
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1R
1V
OpenGL and GLUT Overview
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What is OpenGL & what can it do for me?
OpenGL in windowing systems
Why GLUT
A GLUT program template
What is a “library”.
• Static
• Dynamic
Relationship between OpenGL GLU and windowing APIs.
•OpenGL applications use the window system’s window, input, and
event mechanism
•GLU supports quadrics, NURBS, complex polygons, matrix
utilities, and more
What Is OpenGL?
• Graphics rendering API
– high-quality color images composed of
geometric and image primitives
– window system independent
– operating system independent
OpenGL Library Functions
GL
GL library contains all primitive and attribute functions
associated with OpenGL
GLU
GLU library builds on the GL library to include more
complex primitives (e.g. spheres) and convenience functions
GLUT
GLUT (GL Utility Toolkit) includes functions to interface
with the native window system, including window creation,
management of input devices
Related APIs
• AGL, GLX, WGL
– glue between OpenGL and windowing systems
• GLU (OpenGL Utility Library)
– part of OpenGL
– NURBS, tessellators, quadric shapes, etc.
• GLUT (OpenGL Utility Toolkit)
– portable windowing API
– not officially part of OpenGL
OpenGL and Related APIs
application program
OpenGL Motif
widget or similar
GLX, AGL
or WGL
X, Win32, Mac O/S
GLUT
GLU
GL
software and/or hardware
OpenGL Architecture
Polynomial
Evaluator
CPU
Display
List
Per Vertex
Operations &
Primitive
Assembly
Rasterization
Texture
Memory
Pixel
Operations
Per Fragment
Operations
Frame
Buffer
Features of OpenGL
• Delivers fast and complete 3D
hardware acceleration
• makes real-time 3D effects possible
• designed to support future
innovations in software and
hardware
• Available on many platforms
• Stable
OpenGL as a Renderer
• Geometric primitives
– points, lines and polygons
• Image Primitives
– images and bitmaps
– separate pipeline for images and geometry
• linked through texture mapping
• Rendering depends on state
– colors, materials, light sources, etc.
Other issues
• Rendering acceleration (rasterization,
texture map, spacial subdivision, collision
detection, progressive rendering, view
dependent rendering, image-based
rendering,…)
• Color, Texture, Anti-aliasing
• Animation or simulation
Student 007: “I am dying to see an OpenGL
program !…”
Prof: Be patient, it is only few more
block(diagram)s away !!
Block Diagram
Preliminaries
• Headers Files
• #include <GL/gl.h>
• #include <GL/glu.h>
• #include <GL/glut.h>
• Libraries
• Enumerated Types
– OpenGL defines numerous types for
compatibility
– GLfloat, GLint, GLenum, etc.
GLUT Basics
• Application Structure
– Configure and open window
– Initialize OpenGL state
– Register input callback functions
• render
• resize
• input: keyboard, mouse, etc.
– Enter event processing loop
Sample Program – draw()function
void drawScene(void)
{
// Clear the rendering window
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Set drawing color to white
glColor3f( 1.0, 1.0, 1.0 );
// Draw triangle
glBegin(GL_TRIANGLES);
glColor3f( 1.0, 0.0,
glVertex2f( 1.0, 1.0
glVertex2f( 2.0, 1.0
glVertex2f( 2.0, 2.0
glEnd();
// Flush the pipeline.
glFlush();
}
0.0 );
);
);
);
(Not usually necessary.)
OpenGL Command Formats
glVertex3fv( v )
Number of
components
2 - (x,y)
3 - (x,y,z)
4 - (x,y,z,w)
Data Type
b
ub
s
us
i
ui
f
d
-
byte
unsigned byte
short
unsigned short
int
unsigned int
float
double
Vector
omit “v” for
scalar form
glVertex2f( x, y )
Specifying Geometric Primitives
• Primitives are specified using
glBegin( primType );
glEnd();
– primType determines how vertices are combined
GLfloat red, greed, blue;
Glfloat coords[3];
glBegin( primType );
for ( i = 0; i < nVerts; ++i ) {
glColor3f( red, green, blue );
glVertex3fv( coords );
}
glEnd();
OpenGL Command Syntax
• Function calls: glXxxxx[type] ( [args] )
– Example: glVertex2f (1.0, 2.0);
• Defined constants: GL_XXXXXXXXXX
– Example: GL_COLOR_BUFFER_BIT
• Type definition: GLxxxxxxx
– Example: GLfloat
Command Suffixes/ Argument Data Types
Suffix
Data Type
Typical Corresponding
C-Language Type
OpenGL Type Definition
b
8-bit integer
signed char
GLbyte
s
16-bit integer
short
GLshort
f
32-bit integer
int or long
GLint, GLbyte
i
32-bit floating-point
float
GLfloat, GLclampf
d
64-bit floating-point
double
GLdouble,GLclampd
ub
8-bit unsigned integer
unsinged char
GLubyte,GLboolean
us
16-bit unsinged integer unsinged short
ui
32-bit unsinged integer
unsinged int or
unsinged long
GLushort
GLuint, GLenum,
GLbitfield
Shared Namespace Model
Model
Function
Calls
Application
} Run in same process
Graphics Lib.
OS
glFlush();
unnecessary
O
I
Client-Server Model:
Model
Function
Calls
Application
Graphics
Server
O
Graphics Lib.
OS
OS
Network Protocol
glFlush();
May be necessary
I
OpenGL Architecture
Polynomial
Evaluator
CPU
Display
List
Per Vertex
Operations &
Primitive
Assembly
Rasterization
Texture
Memory
Pixel
Operations
Per Fragment
Operations
Frame
Buffer
State Management and Drawing
in OpenGL
OpenGL Initialization
• Set up whatever state you’re going to use
void init( void )
{
glClearColor( 0.0, 0.0, 0.0, 1.0 );
glClearDepth( 1.0 );
glEnable( GL_LIGHT0 );
glEnable( GL_LIGHTING );
glEnable( GL_DEPTH_TEST );
}
GLUT Callback Functions
• Routine to call when something happens
– window resize or redraw
– user input
– animation
• “Register” callbacks with GLUT
glutDisplayFunc( display );
glutIdleFunc( idle );
glutKeyboardFunc( keyboard );
A Typical Event-Driven Program
Initialization
Main Loop
Event
Handler
Input
Processing
Procedures
Background
Processing
Procedure
Route messages to the
application
Button on Mouse
Window s
Event
Route Event to Correct Application
Window s Application
WinMain()
Message
Left Button Dow n
Message Processed
WinProc()
GLUT Event Processing
Call Idle
Function
No
Event
in
Queue
Yes
Call
Function
n
Call
Function
n
Call
Function
n
Call
Function
Call n
Function n
Pop Event
From Queue
Switch on
Event Type
Callbacks
Event Type
Event A
m1, m2
“Registered” Function
function_A(m1, m2)
Event B
function_B( )
Event C
function_C( )
Event D
Event E
Event F
No Event
Idle function( )
NB: Function parameters must match measures contained
in associated event.
Display Event
Trigger: GLUT determines that the window needs to be
redisplayed. A display event is generated when the window
is first drawn.
Callback function form:
void display();
Registration:
glutDisplayFunc(display);
A display callback function must be registered for each window.
GLUT Mouse Event
Trigger: Any mouse button is depressed or released.
Callback function form:
void mouse_callback_func(int button, int state,
int x, int y);
Registration:
glutMouseFunc(mouse_callback_function);
GLUT Defined Mouse Constants
GLUT_LEFT_BUTTON
GLUT_MIDDLE_BUTTON
GLUT_RIGHT_BUTTON
GLUT_UP
GLUT_DOWN
Systems with only one mouse button can only generate
a GLUT_LEFT_BUTTON callback.
GLUT Reshape Event
Trigger: Active window is resized
Callback function form:
void reshape_func(GLsizei w, GLsizei h);
Registration:
glutReshapeFunc(reshape_func);
GLUT Move Event
Trigger: The mouse is moved while one or more mouse
buttons are pressed.
Callback function form:
void motion_func(int x, int y);
Registration:
glutMotionFunc(motion_func);
GLUT Keyboard Event
Trigger: Any key is depressed.
Callback function form:
void keyboard_function(unsigned char key,
int x, int y);
Registration:
glutKeyboardFunc(keyboard_function);
Idle Callbacks
• Use for animation and continuous update
glutIdleFunc( idle );
void idle( void )
{
t += dt;
glutPostRedisplay();
}
Other Defined Events in GLUT
glutPassiveMotionFunc
glutVisibilityFunc
glutEntryFunc
glutSpecialFunc
glutSpaceballMotionFunc
glutSpaceballRotateFunc
glutSpaceballButtonFunc
glutButtonBoxFunc
glutDialsFunc
glutTabletMotionFunc
glutTabletButtonFunc
glutMenuStatusFunc
Simple GLUT Window
Management Functions
glutInit(int *argc, char** argv);
Initializes a window session.
glutCreateWindow(char *name);
Creates a window with title *name.
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
Sets the display mode to single buffered and RGB color.
glutInitWindowSize (GLsizei h, GLsizei w);
Sets initial window size to h x w.
glutInitWindowPosition(x,y);
Sets initial window position to (x, y).
• TA help is there, but use “Help” and try to
help yourselves !!
• Show simple demo program
OpenGL in MS Windows
GL Commands
OpenGL Lib
GDI Processor
Graphics
Hardware
GDI – Graphics Device Interface (Windows-specific)
Basic Program Skeleton
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Header files, Global variables
Rendering initialization
Keyboard / Mouse functions
Drawing / animation
Window resizing
Idle function
main()
Try this …
Draw a red line in a window with black background
Try changing line thickness
Change color combination
What if you want a regular triangle as against a “filled” one
Now try drawing various figures from the library
Try modeling concave polygons