Today …

• The rendering pipeline in detail

• What is OpenGL

• First OpenGL program

• Details about modeling

Basic Rendering Pipeline

Projection

Illumination

Rasterization&Clipping &Display

1V

1R

N

L

Database of 3D models

Modeling Transformation(OS -> WS)

VisibilityCulling

ViewingTransformation (WS -> CS)

OpenGL and GLUT Overview

• 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

•OpenGL applications use the window system’s window, input, and event mechanism •GLU supports quadrics, NURBS, complex polygons, matrix utilities, and more

Relationship between OpenGL GLU and windowing APIs.

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

GLU

GL

GLUT

GL library contains all primitive and attribute functionsassociated with OpenGL

GLU library builds on the GL library to include morecomplex primitives (e.g. spheres) and convenience functions

GLUT (GL Utility Toolkit) includes functions to interfacewith 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

GLUT

GLU

GL

GLX, AGLor WGL

X, Win32, Mac O/S

software and/or hardware

application program

OpenGL Motifwidget or similar

OpenGL Architecture

DisplayList

PolynomialEvaluator

Per VertexOperations &

PrimitiveAssembly

RasterizationPer Fragment

OperationsFrameBuffer

TextureMemory

CPU

PixelOperations

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()functionvoid 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 triangleglBegin(GL_TRIANGLES);

glColor3f( 1.0, 0.0, 0.0 );glVertex2f( 1.0, 1.0 );glVertex2f( 2.0, 1.0 );glVertex2f( 2.0, 2.0 );

glEnd();

// Flush the pipeline. (Not usually necessary.) glFlush();}

OpenGL Command Formats

glVertex3fv( glVertex3fv( vv ) )

Number ofNumber ofcomponentscomponents

2 - (x,y) 2 - (x,y) 3 - (x,y,z)3 - (x,y,z)4 - (x,y,z,w)4 - (x,y,z,w)

Data TypeData Typeb - byteb - byteub - unsigned byteub - unsigned bytes - shorts - shortus - unsigned shortus - unsigned shorti - inti - intui - unsigned intui - unsigned intf - floatf - floatd - doubled - double

VectorVector

omit “v” foromit “v” forscalar formscalar form

glVertex2f( x, y )glVertex2f( x, y )

Specifying Geometric Primitives• Primitives are specified using

glBegin( glBegin( primType primType ););

glEnd();glEnd();

– primType determines how vertices are combinedGLfloat red, greed, blue;GLfloat red, greed, blue;Glfloat coords[3];Glfloat coords[3];glBegin( glBegin( primType primType ););for ( i = 0; i < nVerts; ++i ) { for ( i = 0; i < nVerts; ++i ) { glColor3f( red, green, blue );glColor3f( red, green, blue ); glVertex3fv( coords );glVertex3fv( coords );}}glEnd();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 D ata Type Typ ica l C orresponding C -Language Type

O penG L Type D efin ition

b 8-b it in teger s igned char G Lbyte

s 16-b it in teger short G Lshort

f 32-b it in teger in t o r long G Lin t, G Lbyte

i 32-b it floating -po in t floa t G Lfloat, G Lclam pf

d 64-b it floating-po in t doub le G Ldouble ,G Lclam pd

ub 8-b it unsigned in teger unsinged char G Lubyte,G Lboolean

us 16-b it unsinged in teger unsinged short G Lushort

u i 32-b it unsinged in teger unsinged in t o r unsinged long

G Luin t, G Lenum , G Lbitfie ld

Shared Namespace ModelModel

Application

Graphics Lib.

O I

FunctionCalls

OS

} Run in same process

glFlush();unnecessary

Client-Server Model:

GraphicsServer

O

I

Network Protocol

Model

Application

Graphics Lib.

FunctionCalls

OS OS

glFlush();May be necessary

OpenGL Architecture

DisplayList

PolynomialEvaluator

Per VertexOperations &

PrimitiveAssembly

RasterizationPer Fragment

OperationsFrameBuffer

TextureMemory

CPU

PixelOperations

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 GLUTglutDisplayFunc( display );

glutIdleFunc( idle );

glutKeyboardFunc( keyboard );

A Typical Event-Driven Program

Initialization

Main Loop

InputProcessingProcedures

BackgroundProcessingProcedure

EventHandler

Route messages to the application

EventButton on Mouse

Windows Route Event to Correct Application

Windows Application

WinMain()

WinProc()

Message

Left Button Down

Message Processed

CallFunction n

GLUT Event Processing

Eventin

Queue

Pop EventFrom Queue

CallFunction n

Switch onEvent Type

CallFunction n

Call IdleFunction

No

Yes

CallFunction nCall

Function nCallFunction n

Callbacks

Event A

Event B

Event C

Event D

Event E

Event F

No Event Idle function( )

m1, m2 function_A(m1, m2)

function_B( )

function_C( )

Event Type “Registered” Function

NB: Function parameters must match measures contained in associated event.

Display EventTrigger: GLUT determines that the window needs to be redisplayed. A display event is generated when the windowis 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_BUTTONGLUT_MIDDLE_BUTTONGLUT_RIGHT_BUTTON

GLUT_UPGLUT_DOWN

Systems with only one mouse button can only generatea 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 mousebuttons 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 updateglutIdleFunc( idle );

void idle( void ){ t += dt; glutPostRedisplay();}

Other Defined Events in GLUTglutPassiveMotionFuncglutVisibilityFuncglutEntryFuncglutSpecialFuncglutSpaceballMotionFuncglutSpaceballRotateFuncglutSpaceballButtonFuncglutButtonBoxFuncglutDialsFuncglutTabletMotionFuncglutTabletButtonFuncglutMenuStatusFunc

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 Lib

GL Commands

GDI Processor

GraphicsHardware

OpenGL in MS Windows

GDI – Graphics Device Interface (Windows-specific)

Basic Program Skeleton

• 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 backgroundTry changing line thicknessChange color combinationWhat if you want a regular triangle as against a “filled” oneNow try drawing various figures from the libraryTry modeling concave polygons