opengl

Transkript

opengl

OPENGL
Y. Doç. Dr. Aybars UĞUR
Ocak 2006
OpenGL Nedir?
OpenGL (Open Graphics Library),
grafik donanımını kullanmak için hazırlanmış
bir yazılım arayüzüdür.
Bu kütüphane yardımıyla, 2B (Boyutlu) ve 3B Grafiksel
nesneler ve işlemler, kolaylıkla tanımlanabilmektedir.
Programlama dillerindeki önemli bir eksikliği
gidermektedir.
İki ve üç boyutlu etkileşimli grafikler içeren yazılımlar
geliştirmek için kullanılan 250 farklı komutu (200’ü
OpenGL’in kendi içinde, 50’si de OpenGL Utility
Library yani glut içinde olmak üzere) içermektedir.
Grafik donanımlarının gücünden yararlanmaktadır.
Ocak 2006
Dr. Aybars UĞUR
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OpenGL : Bazı Özellikler
İşletim Sistemi bağımsızdır (Windows 95/98/NT/2000...,
Linux, Unix, MacOS, BeOS). Windows’ta standart
olarak gelir.
Programlama Dili bağımsızdır. Kütüphane, C, C++, C#,
Java, Visual Basic, Delphi, Fortran, Perl gibi dillerden
kullanılabilmektedir.
Pencere yöneticilerinden bağımsızdır. Sisteme özgü ekler
yapılmazsa, programlar, Win32, X-Window gibi tüm
pencere yöneticileri ile sorunsuz çalışır.
Pencere, fare ve klavye işlemlerinden bağımsız hale
getirmek için kullanılan glut, birçok işletim sistemine
aktarılmıştır.
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Dr. Aybars UĞUR
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OpenGL Temelleri
Red Book’tan yararlanınız…
OpenGL bir “durum makinesidir” :
Çokgenler, etkin (current) renk,
dönüşüm, çizim modu vs. etkilenir.
OpenGL Spesifikasyonundaki herşey,
tüm gerçekleştirimlerinde desteklenir.
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OpenGL RedBook - II
Chapter 1, "Introduction to
OpenGL,"
Chapter 2, "State Management and
Drawing Geometric Objects,"
Chapter 3, "Viewing,"
Chapter 4, "Color,"
Chapter 5, "Lighting,"
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OpenGL RedBook - II
Chapter 6, "Blending, Antialiasing,
Fog, and Polygon Offset,"
Chapter 7, "Display Lists,"
Chapter 8, "Drawing Pixels,
Bitmaps, Fonts, and Images,"
Chapter 9, "Texture Mapping,"
Chapter 10, "The Framebuffer,"
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OpenGL RedBook - III
Chapter 11, "Tessellators and
Quadrics,"
Chapter 12, "Evaluators and
NURBS,"
Chapter 13, "Selection and
Feedback,"
Chapter 14, "Now That You Know,"
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OpenGL ve
Visual C++ 6.0
Bu ders notları, basit olarak Visual C’de OpenGL
kullanımını anlatmak üzere hazırlanmıştır. OpenGL’in
diğer programlama dillerinden kullanımı benzer
şekildedir.
Örnek programlar hazırlandıktan sonra, Visual C++ 6.0
kullanılarak çalıştırılmış ve test edilmiştir. Örnekleri
çalıştırabilmek için VC++ 6.0 yüklendikten sonra
GLUT’un eklenmesi gerekmektedir.
Glut’un güncel sürümü, aşağıda belirtilen adresten
indirilebilmektedir :
http://www.xmission.com/~nate/opengl.html
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Glut’un Kurulumu
Visual C++ 6.0 yüklendikten sonra, GLUT’un kurulması :
GLUT Version 3.7.6 (117 KB) içindeki
“GLUT32.DLL“, \Windows\System klasörüne (NT tabanlı ise
WINNT\System)
“GLUT.H“, \Program Files\Microsoft Visual
Studio\VC98\Include\GL klasörüne
“GLUT.LIB“, \Program Files\Microsoft Visual Studio\VC98\Lib
klasörüne kopyalanır.
Proje ayarları
Project-Settings-Link-Object/Library Modules’de başa :
opengl32.lib glut32.lib eklenir.
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Using OpenGL & GLUT in
Visual Studio .NET 2003
GLUT.H
C:\Program Files\Microsoft Visual Studio
.NET 2003\Vc7\PlatformSDK\Include\gl
GLUT.LIB
C:\Program Files\Microsoft Visual Studio
.NET 2003\Vc7\PlatformSDK\Lib
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Glut : Başlangıç
int main (int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_DEPTH | GLUT_DOUBLE |
GLUT_RGBA);
glutInitWindowSize (windowWidth, windowHeight);
glutInitWindowPosition (0, 0);
glutCreateWindow (“248 Video Game!");
SetStates();
RegisterCallbacks();
glutMainLoop();
return 0;
// Initialize rendering states*
// Set event callbacks*
// Start GLUT
}
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İlk OpenGL Programı :
Pencere Açmak
#include <GL/glut.h>
void init(void)
{
glClearColor(1.0,1.0,1.0,0.0);
glShadeModel(GL_FLAT);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glutSwapBuffers();
}
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int main(int argc, char **argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowSize(400,100);
glutInitWindowPosition(100,100);
glutCreateWindow("Merhaba");
init();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}
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OpenGL Double Buffering
Double buffering:
– Draw on back buffer while front
buffer is being displayed.
– When finished drawing, swap the
two, and begin work on the new
back buffer.
– glutSwapBuffers();
Primary purpose: eliminate flicker
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VC++ Programının
İşletimi
File-New-Workspaces’den yeni bir
Workspace açılır.
File-New-Files-C++ Source File ile
C++ Kaynak Kodu sayfası açılır.
Program yazılır veya belgeden
kopyalanır.
Derlenip çalıştırılır.
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OpenGL Komut Yapısı
glColor3f
OpenGL
komutu
öneki
Ocak 2006
parametre
veri tipi
(float)
OpenGL Komutun
üç
komutu
parametre
Komutu
alan tipi
oluşturan
kelimeler
büyük
harfle
başlar
Dr. Aybars UĞUR
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OpenGL Sabit Yapısı
GL_COLOR_BUFFER_BIT
Sabitler GL_ ile başlar
Tümü büyük harftir
Kelimeleri ayırmada alt çizgi kullanılır
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Nesne Köşelerini Belirtme
Nesneler köşeleri ile belirtilir :
– glVertex3f (2.0, 4.1, 6.0);
– glVertex2i (4, 5);
Etkin Renk köşeleri etkiler :
– glColor3f (0.0, 0.5, 1.0);
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Üçgen Oluşturma
Şeklin köşeleri, glBegin(mode) ve
glEnd() bloğu içinde ve saat yönü
(counter-clockwise) sırasında yazılır.
glBegin (GL_TRIANGLES);
glVertex2i (0, 0);
glVertex2i (2, 0);
glVertex2i (1, 1);
glEnd();
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Şekil Oluşturma
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Primitive (İlkel) Türleri
glBegin için
Points
Lines
GL_POINTS
GL_LINES,
GL_LINE_STRIP,
GL_LINE_LOOP
Triangles GL_TRIANGLES,
GL_TRIANGLE_STRIP,
GL_TRIANGLE_FAN
Quads
GL_QUADS,
GL_QUAD_STRIP
Polygons GL_POLYGON
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Temel Geometrik Tipler
GL_POINTS individual points
GL_LINES pairs of vertices interpreted as individual line segments
GL_LINE_STRIP series of connected line segments
GL_LINE_LOOP same as above, with a segment added between last
and first vertices
GL_TRIANGLES triples of vertices interpreted as triangles
GL_TRIANGLE_STRIP linked strip of triangles
GL_TRIANGLE_FAN linked fan of triangles
GL_QUADS quadruples of vertices interpreted as four-sided polygons
GL_QUAD_STRIP linked strip of quadrilaterals
GL_POLYGON boundary of a simple, convex polygon
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İki Boyut ve
Koordinat Sistemi
OpenGL, iki boyutlu grafikler için birçok
alternatif içermektedir. Basit bir dikdörtgen
çizmek için aşağıdaki kod bloğu kullanılır :
glBegin( GL_QUADS );
glColor3f( 1.0, 0.0, 0.0 );
glVertex2f( 0.0, 0.0 );
glVertex2f( 0.9, 0.0 ); (-1,-1)
glVertex2f( 1.0, 1.0 );
glVertex2f( 0.0, 0.5 );
glEnd();
Ocak 2006
Dr. Aybars UĞUR
(1,1)
22
Renkler
Kırmızı Yeşil Mavi
glColor3f(0.0, 0.0, 0.0);
black
glColor3f(1.0, 0.0, 0.0);
red
glColor3f(0.0, 1.0, 0.0);
green
glColor3f(1.0, 1.0, 0.0);
yellow
glColor3f(0.0, 0.0, 1.0);
blue
glColor3f(1.0, 0.0, 1.0);
magenta
glColor3f(0.0, 1.0, 1.0);
cyan
glColor3f(1.0, 1.0, 1.0);
white
glColor3f(0.9, 0.9, 0.9);
light gray
glColor3f(0.3, 0.3, 0.3);
dark gray
Tüm renkler, üç ana rengin (r, g, b) bileşiminden oluşur.
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Örnek 2 :
Mavi Dikdörtgen Çizmek
#include <gl/glut.h>
void init(void)
{
}
void Draw_A_Rectangle(void)
{
glBegin(GL_QUADS);
glColor3f(0.0,1.0,0.0);
glVertex2f(0.25,0.25);
glColor3f(1.0,1.0,0.0);
glColor3f(1.0,0.0,0.0);
glColor3f(0.0,0.0,1.0);
glEnd();
}
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void display(void)
{
Draw_A_Rectangle();
glutSwapBuffers();
}
int main(int argc,char **argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE |
GLUT_RGB);
glutCreateWindow(" Rectangle ");
init();
glutMainLoop();
return 0;
}
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Çokgen Üzerinde
Renk Geçişi
glShadeModel(GL_SMOOTH);
void Draw_A_Rectangle(void)
{
glBegin(GL_QUADS);
glColor3f(0.0,1.0,0.0);
glColor3f(1.0,1.0,0.0);
glColor3f(1.0,0.0,0.0);
glColor3f(0.0,0.0,1.0);
glEnd();
}
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Dr. Aybars UĞUR
GL_FLAT
25
OpenGL: Shading
OpenGL supports 2 basic shading
models: flat and smooth.
glShadeModel(GL_SMOOTH);
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Örnek 3 :
Döngü ile Çokgen Oluşturma
#include <gl/
gl/glut.h>
glut.h>
#include <math.h>
math.h>
void init(
init(void)
void)
{
}
void Draw_
Draw_Polygon(
Polygon(void)
void)
{
double M_PI = 3.1415, angle;
angle;
glColor3f(0.0,1.0,0.0);
glBegin (GL_LINE_LOOP);
for (int j=0; j<10; j++) {
angle = 2*M_PI*j/10;
glVertex2f (cos
(cos((angle),
angle),
sin(angle
));
sin(angle));
}
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glEnd();
glEnd();
}
void display(
display(void)
void)
{
Draw_
Draw_Polygon();
Polygon();
glutSwapBuffers();
glutSwapBuffers();
}
int main(
main(int argc,
argc,char **argv
**argv))
{
glutInit(&
argc,,argv);
glutInit(&argc
argv);
glutInitDisplayMode(GLUT_DOUBLE
glutInitDisplayMode(GLUT_DOUBLE |
GLUT_RGB);
glutCreateWindow("
glutCreateWindow(" Polygon ");
init();
init();
glutDisplayFunc(
display);
glutMainLoop();
glutMainLoop();
return 0;
Dr. Aybars }UĞUR
27
GLUT Event Callbacks
Register functions that are called when certain
events occur.
Examples:
glutDisplayFunc( Display );
glutKeyboardFunc( Keyboard );
glutReshapeFunc( Reshape );
glutMouseFunc( Mouse );
glutPassiveMotionFunc( PassiveFunc );
glutMotionFunc( MouseDraggedFunc );
glutIdleFunc( Idle );
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Etkileşim : Klavye
void keyboard(unsigned char key, int x, int y)
{
switch(key)
{
case 'x' :
axis = X;
Main’e Eklenmesi gereken :
spin();
glutPostRedisplay();
break;
case 'y' :
glutKeyboardFunc(keyboard);
axis = Y;
spin();
glutPostRedisplay();
break;
default :
break;
}
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} Ocak 2006
Etkileşim : Fare
void mouse(int button, int state, int x, int y)
{
switch (button) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(spinDisplay);
Main’e Eklenmesi gereken:
break;
case GLUT_MIDDLE_BUTTON:
glutMouseFunc(mouse);
if (state == GLUT_DOWN)
glutIdleFunc(NULL);
break;
default:
break;
}
}
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30
OPENGL : 3D CONCEPTS
The camera initially
points down the
negative z-axis.
(You're seeing the
back of the camera.)
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Summary of 3D
Transformation
3D Object Coordinates
P(x, y, z)
Modeling
Modeling
Transformation
Transformation
3D World Coordinates
Viewing
Viewing
Transformation
Transformation
3D Viewing Coordinates
Projection
Projection
Transformation
Transformation
2D Projection Coordinates
Window-to-Viewport
Window-to-Viewport
Transformation
Transformation
2D Device Coordinates
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P(x, y)Dr. Aybars UĞUR
32
The Camera
Analogy
To take a photograph with a
camera, steps might be
• Set up your tripod and pointing the
camera at the scene (viewing trans.)
• Arrange the scene to be
photographed into the desired
composition (modoling trans.)
• Choose a camera lens or adjust the
zoom (projection trans.)
• Determine how large you want the
final photograph to be - for example,
you might want it enlarged (viewport
trans.)
• After these steps are performed, the
picture can be snapped or the scene
can be drawn.
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Stages of Vertex Transform
• Modelview matrix: orients the model and the camera relative to
each other.
• Projection matrix: specifies the shape and orietation of the viewing
volume.
• Viewport transformation: controls the conversion of 3D model
coordinates to screen coordinates.
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Example: Drawing Cube 1
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel (GL_FLAT);
}
void display(void)
{
glClear (GL_COLOR_BUFFER_BIT);
glColor3f (1.0, 1.0, 1.0);
glLoadIdentity ();
/* clear the matrix */
/* viewing transformation */
gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glScalef (1.0, 2.0, 1.0);
/* modeling transformation */
glutWireCube (1.0);
glFlush ();
}
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void reshape (int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glFrustum (-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
glMatrixMode (GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
init ();
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
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Viewing Transformation
• Analogus to positioning and aiming the camera.
• Usage: gluLookAt()
• Arguments indicate where the camera (eye position) is placed,
where it is aimed, and which way is up.
• In the example, we place the camera at (0, 0, 5), aim the camera
lens toward (0, 0, 0) and specify the up-vector as (0, 1, 0)
• By default the camera is at the origin (0, 0, 0), points down the
negative z-axis and has an up-vector of (0, 0, 1)
Modeling Transformation
• Analogous to positioning and orienting the model.
• Uasge: glScalef()
• Arguments specify how scaling should occur along the 3 axes.
• In the example, the cube is drawn twice as large in the y
direction
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Projection Transformation
• Similar to choosing a lens for a camera as determining what the
field of view (FOV) or viewing volume is.
• In addition, it determines how objects are projected onto screen.
• Usage: glFrustum()
• Arguments describe values of left, right, bottom, top, near and
far for a viewing volume.
• Before calling glFrustum(), glMatrixMode() with the argument
GL_PROJECTION must be called.
• After calling glFrustum(), the matrix stack must be set back to
GL_MODELVIEW
• Take care the current matrix with glLoadIdentity()
Note: Default matrix stack is GL_MODELVIEW
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Viewport Transformation
• Indicates the region of available screen area into which the scene
is mapped.
• Usage: glViewport()
• The arguments describe the origin, the width and height of the
region within the window.
What does OpenGL do when all transformations have been
specified?
• Transforms each vertex of every object in the scene by the
modeling and viewing transformations.
• Transforms the vertices and clips the objects by the projection
transformations
• Divides the remaining transformed vertices with w and maps
them onto the viewport.
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Let’s Think About Transformations
In general, the order of transformation is critical
• If oyu do transformation A and then transformation B, you almost
always get something different than you do them the the
opposite order.
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Transformations
and Viewing
OpenGL has 3 different matrix
modes:
– GL_MODELVIEW
– GL_PROJECTION
– GL_TEXTURE
Choose the matrix with:
glMatrixMode(…);
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Modelview matrix
Transforms objects within the scene.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(10.5, 0, 0);
glRotatef(45, 0, 0, 1);
DrawCube();
Remember that the operations are right
multiplied, so the transformation just
before DrawCube() takes effect first.
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Modeling
Transformations
void glTranslate{fd}(TYPE x,
TYPE y, TYPE z);
Multiplies the current matrix
by a matrix that moves
(translates) an object by
the given x, y, and z values
(or moves the local
coordinate system by the
same amounts).
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Üç Boyutlu Dönüşümler
glRotate produces a rotation of angle degrees
around the vector (x,y,z).
– void glRotated( GLdouble angle, GLdouble x, GLdouble y,
GLdouble z)
– void glRotatef( GLfloat angle, GLfloat x, GLfloat y, GLfloat z )
glScale produces a nonuniform scaling along the x,
y, and z axes.
void glScaled( GLdouble x, GLdouble y, GLdouble z )
void glScalef( GLfloat x, GLfloat y, GLfloat z )
glTranslate produces a translation by (x,y,z).
void glTranslated( GLdouble x, GLdouble y, GLdouble z )
void glTranslatef( GLfloat x, GLfloat y, GLfloat z )
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OpenGL Matrix Stacks
glLoadIdentity(void);
Clears the currently modifiable matrix for future
transformation instructions.
Typically we call this instruction before specifying
modeling, viewing or projection transformations.
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Manipulating stacks: the OpenGL calls to push, pop,
or multiply top of stack
glLoadMatrix(void);
glMultMatrix(void);
glPushMatrix(void); the topmost matrix is copied
glPopMatrix(void); the topmost matrix is destroyed
All vertices of the object are multiplied by the matrix.
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Manipulating stacks: the OpenGL calls to push, pop,
or multiply top of stack
glLoadMatrix(const type *m);
glMultMatrix(const type *m);
m1 m5
m9 m13
m2 m6 m10 m14
m3 m7 m11 m15
m4 m8 m12 m16
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Matrix Stacks
OpenGL supports two stacks of matrices
– Modelview matrix stack (4x4 matrices)
– Projection matrix stack (4x4 matrices)
These stacks are useful for constructing
hierarchical models. For example a car
made of its body and the four wheels:
Rotate wheels
+ Rotate body
Rotate wheels
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Matrix Stacks
glPushMatrix(void) - Pushes
all matrices in the current stack
down one level.
glPopMatrix(void) - Pops the
top matrix off the current stack,
losing the topmost matrix!
(The current stack is determined
by glMatrixMode).
Current
matrix
level
M4
M3
M2
M4
Push
M1
M4
M3
M2
M1
M5
Current
matrix
level
M4
M5
M4
M3
M2
Pop
M3
M2
M1
M1
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Matrix Stacks
Example code:
void drawCar() {
glMatrixMode(GL_MODELVIEW) ;
glTranslatef(x,y,z) ;
/*/
glRotatef(car_ang, 0, 1, 0) ;
/*/
draw_car_body() ;
glPushMatrix() ;
glTranslate(-1,0,1) ;
glRotatef(wheels_ang, 0, 1, 0) ;
draw_car_wheel() ;
glPopMatrix() ;
glPushMatrix() ;
glTranslate(1,0,1) ;
glRotatef(wheels_ang, 0, 1, 0) ;
draw_car_wheel() ;
glPopMatrix() ;
}
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First we move and rotate
the car (body + wheels) as it is the top level in the
hierarchy.
Next we push the stack and therefore store a
copy.
Then we draw the right
and left wheels in their
appropriate position and
orientation. Note that on
each wheel the
transformation /*/ will
operate.
The last pop will retrieve
the matrix containing only
the /*/ transformations.50
3D GLUT predefined
shapes
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Üç Boyutlu Hazır Nesneler
I
glutSolidSphere, glutWireSphere
glutSolidCube, glutWireCube
glutSolidCone, glutWireCone
glutSolidTorus, glutWireTorus
glutSolidDodecahedron, glutWireDodecahedron
glutSolidOctahedron, glutWireOctahedron
glutSolidTetrahedron, glutWireTetrahedron
glutSolidIcosahedron, glutWireIcosahedron
glutSolidTeapot, glutWireTeapot
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Üç Boyutlu Hazır Nesneler
II
glutSolidCone - render a solid or wireframe cone respectively.
glutWireCone
glutSolidCube - render a solid or wireframe cube respectively.
glutSolidDodecahedron - render a solid or wireframe
dodecahedron (12-sided regular solid) respectively.
glutSolidIcosahedron - render a solid or wireframe
icosahedron (20-sided regular solid) respectively.
glutSolidOctahedron - render a solid or wireframe
octahedron (8-sided regular solid) respectively.
glutSolidSphere - render a solid or wireframe sphere
respectively.
glutSolidTeapot - render a solid or wireframe teapot
respectively.
glutSolidTetrahedron - render a solid or wireframe
tetrahedron (4-sided regular solid) respectively.
glutSolidTorus - render a solid or wireframe torus
(doughnut) respectively.
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Projection Matrix – I
Sets up a perspective projection.
– glFrustrum (...);
– gluPerspective (fovy,
aspect, near, far);
– glOrtho (...);
– gluLookAt (...);
(often applied to modelview matrix)
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Projection Matrix - II
Example:
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(64, (float)windowWidth /
(float)windowHeight, 4, 4096);
gluLookAt(0.0, 0.0, 2.0, // camera position
0.0, 0.0, 0.0, // target position
0.0, 0.0, 2.0);// up vector
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Perspective Viewing Volume
Specified by gluPerspective()
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Viewing Transformations
Default camera position
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gluLookAt(4.0, 2.0, 1.0, 2.0, 4.0, -3.0, 2.0, 2.0, -1.0);
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The viewport transformation specifies the rectangular
region of the window where the model is drawn.
void glViewport(GLint x, GLint y, GLsizei width, GLsizei
height);
Defines a pixel rectangle in the window into which the final
image is mapped. The (x, y) parameter specifies the lowerleft corner of the viewport, and width and height are the
size of the viewport rectangle. By default, the initial
viewport values are (0, 0, winWidth, winHeight), where
winWidth and winHeight are the size of the window.
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The aspect ratio of a viewport should generally equal to the
aspect ratio of the viewing volume.
gluPerspective(fovy, 1.0, near, far);
glViewport(0, 0, 400, 400);
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gluPerspective(fovy, 1.0, near, far);
glViewport (0, 0, 400, 200);
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Sample Viewport
Application
// top left: top view
glViewport(0, win_height/2, win_width/2, win_height/2);
glLoadIdentity();
glOrtho(-3.0, 3.0, -3.0, 3.0, 1.0, 50.0);
gluLookAt(0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -1.0);
glLoadIdentity();
glCallList(object);
// top right: right view
glViewport(win_width/2, win_height/2, win_width/2, win_height/2);
glLoadIdentity();
glOrtho(-3.0, 3.0, -3.0, 3.0, 1.0, 50.0);
gluLookAt(5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glLoadIdentity();
glCallList(object);
// bottom left: front view
glViewport(0, 0, win_width/2, win_height/2);
glLoadIdentity();
glOrtho(-3.0, 3.0, -3.0, 3.0, 1.0, 50.0);
gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glLoadIdentity();
glCallList(object);
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// bottom right: rotating perspective view
glViewport(win_width/2, 0, win_width/2, win_height/2);
glLoadIdentity();
gluPerspective(70.0, 1.0, 1, 50);
gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glLoadIdentity();
glRotatef(30.0, 1.0, 0.0, 0.0);
glRotatef(Angle, 0.0, 1.0, 0.0);
glCallList(object);
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OpenGL : Setting Up
Rendering States
OpenGL is a state machine: polygons are affected
by the current color, transformation, drawing
mode, etc.
Enable and disable features such as lighting,
texturing, and alpha blending.
– glEnable (GL_LIGHTING);
– glDisable (GL_FOG);
Forgetting to enable something is a common
source of bugs!
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OpenGL:
Normals and Lighting
OpenGL can do lighting computations for you
Normal vectors should be of unit length
(normalized) in most cases.
Normal vector kept as state – each vertex is
assigned the most recently set normal vector
...
glNormal3fv
glVertex3fv
glVertex3fv
glVertex3fv
...
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(n0);
(v0);
(v1);
(v2);
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OpenGL: Lighting
glEnable (GL_LIGHTING);
OpenGL supports a minimum of 8 lights.
glEnable (GL_LIGHT0);
(GL_LIGHT7);
...
glEnable
Lights have a position, type, and color,
among other things (more details in text).
Types of lights are point light, directional
light, and spotlight.
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Lighting in OpenGL
GLfloat amb0[] = {0.2, 0.4, 0.6, 1.0};
GLfloat diff0[] = {0.8, 0.9, 0.5, 1.0};
GLfloat spec0[] = {1.0, 0.8, 1.0, 1.0};
glLightfv(GL_LIGHT0, GL_AMBIENT, amb0);
//attach them to LIGHT0
glLightfv(GL_LIGHT0, GL_DIFFUSE, diff0);
glLightfv(GL_LIGHT0, GL_SPECULAR, spec0);
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OpenGL:
Material Properties
Material properties are associated with each
polygon (corresponding light properties)
– glMaterial*(GLenum face, GLenum
pname, TYPE param);
Some properties (pname) :
–
–
–
–
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GL_AMBIENT: Ambient color of material
GL_DIFFUSE: Diffuse color of material
GL_SPECULAR: Specular component (for highlights)
GL_SHININESS: Specular exponent (intensity of
highlight)
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OpenGL: Texturing
Mapping the texture to the polygon
– specify (s,t) texture coordinates for
(x,y,z) polygon vertices
– texture coordinates (s,t)are from 0,1:
glTexCoord2f(s,t);
(x3,y3,z3) (x1,y1,z1)
0,1
1,1
t
1,1
+
0,0
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s
0,0
1,0
(x0,y0,z0) (x2,y2,z2)
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OpenGL: Alpha Blending
When enabled, OpenGL uses the alpha
channel to blend a new fragment’s color
value with a color in the framebuffer
+
=
New color
(r1,g1,b1,a1)
Color in framebuffer
(r0,g0,b0,a0)
“source”
“destination”
?
(r’,g’,b’,a’)
Useful for overlaying textures or other effects
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OpenGL: Fog
Simulate atmospheric effects
•glFog ():
Sets fog parameters
•glEnable (GL_FOG);
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Rendering Pipeline
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OpenGL: Other Features
Display Lists (ch 7): Speed up your
game!
Quadrics (ch 11): Pre-made objects
– Also look at GLUT’s objects
Evaluators (ch 12): Bezier curves and
surfaces
Selection (ch 13): Clicking on game
objects with a mouse
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CSGL
C Sharp Graphics Library
CSGL
OpenGL’in .NET ortamında kullanımını
sağlayan grafik kütüphanesidir.
Adresler :
– http://sourceforge.net/projects/csgl
– http://csgl.sourceforge.net/
• .NET üzerinde csgl.1.4.1.dll.zip install
dosyasından kurularak program
geliştirmeye başlanabilir.
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Dikdörtgen Çizdiren CSGL
Kodu (1)
using System;
using System.Drawing;
using System.Windows.Forms;
using CsGL.OpenGL;
public class RectDemo : Form
{
MyView view = new MyView();
public static void Main()
{
RectDemo di = new
RectDemo();
Application.Run( di );
}
}
public RectDemo()
{
Text = "Rect demo !";
view.Dock = DockStyle.Fill;
Controls.Add( view );
}
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Kodu (2)
class MyView : OpenGLControl
{
public override void glDraw()
{
GL.glClear( GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT );
// Clear Screen And Depth Buffer
GL.glBegin( GL.GL_QUADS );
GL.glVertex2i( 10, 10 );
GL.glEnd();
GL.glFlush();
}
protected override void InitGLContext()
{
GL.glClearColor( 1.0f, 1.0f, 1.0f, 0.0f );
GL.glColor3f( 0.0f, 0.0f, 0.0f );
GL.glPointSize( 4.0f );
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Kodu (3)
protected override void OnSizeChanged(EventArgs e)
{
base.OnSizeChanged(e);
GL.glMatrixMode(GL.GL_PROJECTION);
GL.glLoadIdentity();
GL.gluOrtho2D( 0.0, Size.Width, 0.0, Size.Height );
}
}
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KAYNAKLAR
Bilgisayar Grafikleri ders notları,
Aybars UĞUR, Ege Üniversitesi
OpenGL Red Book
Sean Walker ve Ian Buck ders slaytları,
Stanford University
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opengl

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