OpenGL overview (đồ họa máy TÍNH SLIDE)

OpenGL Overview


OpenGL and GLUT Overview

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What is OpenGL & what can it do for me?

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OpenGL in windowing systems

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Why GLUT

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A GLUT program template


What Is OpenGL?

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Graphics rendering API

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a cross-platform API
high-quality color images composed of geometric and image primitives

widely used in CAD, virtual reality, scientific visualization, information visualization and
video game development


OpenGL Architecture


OpenGL as a Renderer

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Geometric primitives

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points, lines and polygons

Image Primitives

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images and bitmaps

separate pipeline for images and geometry

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linked through texture mapping

Rendering depends on state

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colors, materials, light sources, etc.


Related APIs

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AGL, GLX, WGL

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glue between OpenGL and windowing systems

GLU (OpenGL Utility Library)

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part of OpenGL
NURBS, tessellators, quadric shapes, etc.

GLUT (OpenGL Utility Toolkit)

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portable windowing API
keyboard and mouse input
Geometric primitives: cubes, spheres, and teapot
not officially part of OpenGL


OpenGL and Related APIs

application program

OpenGL Motif

GLUT

widget or similar

GLX, AGL
or WGL

X, Win32, Mac O/S

software and/or hardware

GLU
GL


What is JOGL?

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Java OpenGL is a wrapper library by the Game Technology Group at Sun Microsystems
that allow OpenGL to be used in Java.

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The base OpenGL C API is accessed in JOGL via Java Native Interface (JNI) calls.
The straightforward mapping of the OpenGL C API to Java methods.
Other Java OpenGL wrappers: GL4Java, JGL, LWJGL (Light-Weight Java Game Library)


Setting Up JOGL 2.0x

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Download the latest "stable" release from JogAMP

Select "jogamp-all-platforms.7z".

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Setup Library

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Copy the necessary jar-file, native libraries of your operating platform, and source-files into
the appropriate sub-directories
for Win32, copy

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"jar\gluegen-rt.jar", "jar\jogl.all.jar" into "jar";
all files in "lib\windows-i586" into "lib";
"gluegen-java-src.zip", "jogl-java-src.zip" into "src".
Unzip the javadocs downloaded into "javadoc".


Preliminaries

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Headers Files

// must import OpenGL....
im p ort javax.media.opengl.GL2;
// import GL constants
im p ort static javax.media.opengl.GL2.*;
im p ort javax.media.opengl.glu.GLU;
im p ort com.jogamp.opengl.util.gl2.GLUT
im p ort javax.media.opengl.GLAutoDrawable;
im p ort javax.media.opengl.GLCapabilities;
im p ort javax.media.opengl.GLEventListener;
im p ort javax.media.opengl.GLProfile;
im p ort javax.media.opengl.awt.GLJPanel;

...


JOGL Basics

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Create an OpenGL drawable is a surface for graphics rendering: GLCanvas and
GLJPanel.

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Register GLEventListener to handle OpenGL events: init, display, reshape,
dispose

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Register input listeners: keyboard, mouse, etc.

Sample Template Program
p u b lic class JO G L2Tem plate exten ds G LJPanel
im plem ents G LEventListener {
// Setup O penG L G raphics Renderer
p rivate G LU glu; // for the G L U tility
p rivate G LU T glut; // O penG L U tility Toolkit

/** Constructor to setup the G U Ifor this Com ponent */
p u b lic JO G L2Tem plate() {
th is.addG LEventListener(this);
}


Sample Program: init event
/**
* Called back im m ediately after the O penG L context is initialized.
* Can be used to perform one-tim e initialization.Run only once.
*/
p u b lic void init(G LAutoD raw able draw able) {
G L2 gl= draw able.getG L().getG L2(); // get the O penG L graphics context
glu = n ew G LU (); // get G L U tilities
gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // set background color
gl.glClearD epth(1.0f); // set clear depth value to farthest
gl.glEnable(G L_D EPTH _TEST); // enables depth testing
gl.glD epthFunc(G L_LEQ U AL); // the type of depth test to do
// best perspective correction
gl.glH int(G L_PERSPECTIVE_CO RRECTIO N _H IN T,G L_N ICEST);
// blends colors nicely,and sm oothes out lighting

gl.glShadeM odel(G L_SM O O TH );

// ----- Your O penG L initialization code here ----}


Sample Program: reshape event
/* Call-back handler for w indow re-size event.Also called w hen the
draw able is fi
rst set to visible.*/
p u b lic void reshape(G LAutoD raw able draw able,
in t x, in t y, in t w idth, in t height) {
G L2 gl= draw able.getG L().getG L2();
if (height = = 0) height = 1; // prevent divide by zero
fl
o at aspect = (f l
o at) w idth / height;
// Set the view port (display area) to cover the entire w indow
gl.glView port(0, 0, w idth, height);
// Setup perspective projection,
// w ith aspect ratio m atches view port
gl.glM atrixM ode(G L_PRO JECTIO N ); // choose projection m atrix
gl.glLoadIdentity(); // reset projection m atrix
glu.gluPerspective(45.0, aspect, 0.1,100.0); // fovy, aspect,
// Enable the m odel-view transform
gl.glM atrixM ode(G L_M O D ELVIEW );
gl.glLoadIdentity(); // reset
}

zN ear,zFar

Sample Program: display event
/* Called back by the anim ator to perform rendering.*/
p u b lic void display(G LAutoD raw able draw able) {
// get the O penG L 2 graphics context
G L2 gl= draw able.getG L().getG L2();
// clear color and depth buff
ers
gl.glClear(G L_CO LO R_BU FFER_BIT | G L_D EPTH _BU FFER_BIT);
gl.glLoadIdentity(); // reset the m odel-view m atrix

// Your O penG L rendering code here
// (Render a w hite triangle for testing)
gl.glTranslatef(0.0f, 0.0f, -6.0f); // translate into the screen
gl.glBegin(G L_TRIAN G LES); // draw using triangles
gl.glVertex3f(0.0f, 1.0f,0.0f);
gl.glVertex3f(-1.0f,-1.0f,0.0f);
gl.glVertex3f(1.0f, -1.0f, 0.0f);
gl.glEnd();
}


Sample Program: dispose event
**
* C alled back before the O penG L context is destroyed.
* Release resource such as buff
ers.
*/
p u b lic void dispose(G LAutoD raw able draw able) {
}

p u b lic static void m ain(String[] args) {
Sw ingU tilities.invokeLater(new Runnable() {
p u b lic void run() {
// Create the O penG L rendering canvas
G LJPanelpanel= new JO G L2Tem plate();
panel.setPreferredSize(new D im ension(640,480));
// Create a anim ator
FPSAnim ator anim ator = new FPSAnim ator(panel, 60,true);
JFram e fram e = new JFram e();
fram e.getContentPane().add(panel);
fram e.addW indow Listener(new W indow Adapter() {
p u b lic void w indow Closing(W indow Event e) {
// stop the anim ator stops before program exits.
n ew Thread() {
p u b lic void run() {
if (anim ator.isStarted()) anim ator.stop();
System .exit(0);
}
}.start();
}
});
fram e.setTitle("JO G L2 Tem plate");
fram e.pack(); fram e.setVisible(true);
anim ator.start(); // start the anim ation loop
}
});

Elementary Rendering


Elementary Rendering

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Geometric Primitives

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Managing OpenGL State

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OpenGL Buffers


OpenGL Geometric Primitives

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All geometric primitives are specified by vertices

GL_LINES
GL_POLYGON
GL_POINTS

GL_LINE_STRIP

GL_LINE_LOOP

GL_TRIANGLES

GL_QUADS
GL_QUAD_STRIP
GL_TRIANGLE_STRIP

GL_TRIANGLE_FAN


Simple Example

void drawRhombus(GL2 gl, float[] color) {
gl.glColor3fv(color);
gl.glBegin(GL2.G L_Q U AD S);
gl.glVertex2f(0.0f, 0.0f);
gl.glVertex2f(1.0f, 0.0f);
gl.glVertex2f(1.5f, 1.118f);
gl.glVertex2f(0.5f, 1.118f);
gl.glEnd();
}


OpenGL Command Formats
glVertex3fv(v)

Data Type

Number of

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

b

- byte

ub - unsigned byte
s

- short

us - unsigned short
i

- int

ui - unsigned int
f

- float

d

- double

Vector
omit "v" for

scalar form
glVertex2f(x, y)


Enumerated Types

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OpenGL defines numerous types for compatibility:


Specifying Geometric Primitives

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Primitives are specified using
glBegin(primType);
glEnd();

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primType determines how vertices are combined
void drawRhombus(GL2 gl, float[] color) {
gl.glColor3fv(color);
gl.glBegin(GL_QUADS);
gl.glVertex2f(0.0f, 0.0f);
gl.glVertex2f(1.0f, 0.0f);
gl.glVertex2f(1.5f, 1.118f);
gl.glVertex2f(0.5f, 1.118f);
gl.glEnd();

}


OpenGL Color Models

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RGBA or Color Index
color index mode
Red

Green

Blue

0
1

Display

1

2

2

4
8

3

ww
www

16

ww

24

123

219

25
26
www

RGBA mode

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