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Introduction to OpenGL & HW1 Announcement. 劉軒銘 , 網媒所 碩二 ICG 2012 Fall. Introduction to OpenGL & HW1 Announcement. Introduction to openGL Coordinate system and transformations in openGL A simple sample Requirements of HW1 Others. 劉軒銘 , 網媒所 碩二 ICG 2012 Fall. - PowerPoint PPT Presentation
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Introduction to OpenGL &
HW1 Announcement
劉軒銘 , 網媒所 碩二ICG 2012 Fall
Introduction to OpenGL&
HW1 Announcement
劉軒銘 , 網媒所 碩二ICG 2012 Fall
• Introduction to openGL
• Coordinate system and transformations in openGL
• A simple sample
• Requirements of HW1
• Others
Introduction to openGL
A Graphics rendering API introduced in 1992 by Silicon Graphics Inc
Now managed by Khronos Group
Provide the API functions to access graphics hardware directly
Cross-platform
Introduction to openGL
GLU (OpenGL Utility Library)◦Part of OpenGL◦Use the prefix of glu (ex: gluLookAt())
GLUT (OpenGL Utility Toolkit)◦Not officially part of OpenGL◦hide the complexities of differing window
system APIs. ◦Use the prefix of glut
(ex:glutDisplayFunc())
World coordinates
object coordinates
Coordinate system
World coordinates
Camera coordinates
Coordinate system
World coordinates
Camera coordinates
Clip coordinates
Coordinate system
Coordinate system
Model-view
transformation
Projectiontransformat
ionVertices
Worldcoordinates
Cameracoordinates
Clipcoordinates
Vertices
There are two matrix stacks.◦ ModelView matrix (GL_MODELVIEW)◦ Projection matrix (GL_PROJECTION)
CTM
Coordinate system
Model-view
transformation
Projectiontransformat
ionVertices
Worldcoordinates
Cameracoordinates
Clipcoordinates
Vertices
glMatrixMode(GL_MODELVIEW);//now we are in modelview matrix stack!//do modelview transformation here…..
glMatrixMode(GL_PROJECTION);//now we are in projection matrix stack!//do projection transformation here….
When we call functions of transformation, we should change to the appropriate matrix stack first.
openGL as state machine
Put a value into various states, then it will remain in effect until being changed.◦e.g. glColor*()
Many state variables are enabled or disabled with glEnable(), glDisable()◦e.g. glEnable(GL_LIGHT0)
openGL as state machine
glBegin(GL_LINES);
R G BglColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
(1,1,0)
(-1,-1,0)
(-1,1,0)
(1,-1,0)
openGL as state machine
glLoadIdentity();
glTranslatef( distance,0, 0); glRotatef(angleX, 1.0, 0.0, 0.0);glRotatef(angleY, 0.0, 1.0, 0.0);
glBegin(GL_QUADS);glVertex3f(-7, 7, 7);…
glEnd();
(1,1,0)
(-1,-1,0)
(-1,1,0)
(1,-1,0)
Current Transformation
matrix(CTM)
Matrix in OpenGL
Mantain matrix stack◦ glPushMatrix() : used to save current
stack◦ glPopMatrix() : used to restore
previous stack
glPushMatirx()
x
glRotatef glPopMatrix()
13
World coordinates
glBegin(TYPE)glVertex3f(x,y,z)…….
glEnd()
Coordinate system
Primitives
Transformations : Model-View
glMatrixMode(GL_MODELVIEW)//Affine Transformation
glRotatef(angle,direction)glTranslatef(displacement)glScalef(scale coefficients)
glBegin(TYPE)glVertex3f(x,y,z)
………………….glEnd()
World coordinates
Camera coordinates
V’<- [R][T][S] V
glMatrixMode(GL_MODELVIEW)
gluLookAt({eye},{look at},{{up})
//Affine Transformation
glBegin(TYPE)glVertex3f(v0)
glEnd()
World coordinates
Camera
coordinates
Transformations : Model-View
glMatrixMode(GL_PROJECTION)//projection TransformationglOrtho(clipping volume)gluPerspective(fov,ciipping Volume)glFrustrum(clipping volume)
glMatrixMode(GL_MODELVIEW)gluLookAt//Affine TransformationglBegin(TYPE)
glVertex3f(v0)………..
glEnd()
World coordinates
Camera coordinates
Image coordinates
Transformations : Projection
Notice!!
Each affine and projective transformation is implemented as a matrix, the order of function calls plays an important role.
glRotatef
glTranslatef
glScalef
Code:
glBeginglVertex3f……glEnd
Matrix multiplication
gluLookAt
glMatrixMode(GL_MODELVIEW)
glMatrixMode(GL_PROJECTION) gluperspective
= VgluLookAt
glRotatef glTranslatef
glScalef
glVertex3f
gluperspective
A Simple Example
A Simple Example#include <GL/glut.h>
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitWindowSize(600, 800);
glutInitWindowPosition(500, 500);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
glutCreateWindow("ICG simple");
glutReshapeFunc(GL_reshape);
glutDisplayFunc(GL_display);
glutMainLoop();
return 0;
}
A Simple Examplevoid GL_display()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glBegin( GL_LINES );
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
glutSwapBuffers();
}
A Simple Examplevoid GL_display()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glBegin( GL_LINES );
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
glutSwapBuffers();
}
A Simple Examplevoid GL_display()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glBegin( GL_LINES );
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
glutSwapBuffers();
}
A Simple Examplevoid GL_display()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glBegin( GL_LINES );
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
glutSwapBuffers();
}
A Simple Examplevoid GL_display()
{
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glBegin( GL_LINES );
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, -1.0, 0.0);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0, 1.0, 0.0);
glVertex3f(1.0, -1.0, 0.0);
glEnd();
glutSwapBuffers();
}
A Simple Example
void GL_reshape(GLsizei w, GLsizei h){ glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION);
glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f);
}
A Simple Example
void GL_reshape(GLsizei w, GLsizei h){ glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION);
glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f);
}
A Simple Example
void GL_reshape(GLsizei w, GLsizei h){ glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION);
glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f);
}
A Simple Example#include <GL\glut.h>
void GL_reshape(GLsizei w, GLsizei h);void GL_display();
int main(int argc, char** argv){ glutInit(&argc, argv);glutInitWindowSize(600, 800);glutInitWindowPosition(500, 500);glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);glutCreateWindow("ICG simple"); glutReshapeFunc(GL_reshape); glutDisplayFunc(GL_display); glutMainLoop(); return 0;}
void GL_reshape(GLsizei w, GLsizei h){glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f);
}
void GL_display(){glClearColor(0.0f, 0.0f, 0.0f, 0.0f);glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);glLoadIdentity();
glBegin( GL_LINES );glColor3f(0.0f, 1.0f, 0.0f);glVertex3f(1.0, 1.0, 0.0);glVertex3f(-1.0, -1.0, 0.0);glColor3f(1.0f, 0.0f, 0.0f);glVertex3f(-1.0, 1.0, 0.0);glVertex3f(1.0, -1.0, 0.0);glEnd();
glutSwapBuffers();}
Requirements of HW1Due : 10/24
You are required to do the following in homework #1: (6 points )1. Load a 3D model file of TRI format. Draw it in wireframe mode and view it in perspective view.(2 pts) 2. Implement basic transformations such as rotation, translation, scaling and shearing.(3 pts)
3. Object rotation around x , y and z-axis.(4 pts)** You have to make these transformation matrix by yourself in problem 2 and 3** glTranslate , glRotate, glScale are not allowed 4. Clipping implementation. Try to show the difference between clipping and non-clipping. (5 pts)** glOrtho, gluPerspective and glFrustum are not allowed in problem 4
5. Bonus. Any kind of effort you made more than requirements above.(6 pts)
z
x
y
screen at z = 0
clipping box is enclosed by: x = 1,x=-1,y=1,y=-1,z=1,z=-1
Notice!! How does openGL set its clipping volume for window??
Using homogeneous coordinatesclipping box
nonhomogeneous coordinate:
xyzw
, w =/= 1
z
x
y
screen at z = 0
clipping box is enclosed by: x = 1,x=-1,y=1,y=-1,z=1,z=-1
Notice!! How does openGL set its clipping volume for window??
Using homogeneous coordinatesclipping box
homogeneous coordinate:
x/wy/wz/w1
Notice!! How does openGL set its clipping volume for window??
Using homogeneous image coordinatesclipping boxYou’d better set your own homogeneous image
coordinates clipping box different from openGL’s.
※Here the homogeneous image coordinates clipping volume is different from theOne described in textbook , which is refer to camera coordinates clipping volume.
OthersGlut window functions:
glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);glutInitWindowSize(800, 600);glutInitWindowPosition(100, 100);glutCreateWindow(“Name");
glutDisplayFunc(display);glutReshapeFunc(reshape);glutKeyboardFunc(keyboard);glutMouseFunc(mouse);glutMainLoop();
OthersInteractive setting:
void keyboard(unsigned char key, int x, int y){switch(key){
………case 'a':
glClearColor(1., 1., 1., 1.);startPosX -= 10;glutPostRedisplay();break;
}}
OthersInteractive setting:
void mouse(int button, int state, int x, int y){static float preX, preY;switch(state){
case GLUT_DOWN:preX = x;preY = y;glutPostRedisplay();break;
……………….}
}
OthersSetting up openGL(visual C++):
1.download glut-3.7.6-bin.zip or similar - GLUT for Win32 dll, lib and header file - there.
2.Make a directory called "GL" under C:\Program Files\Microsoft Visual Studio 9.0\VC\include or similar
3.Copy the header files into C:\programme\microsoft visual studio\vc98\include\GL
4.Copy all *.lib files into C:\programme\microsoft visual studio\vc98\Lib
5.Copy all .dll files into C:\Windows\System32
6.In the Menu of VC++ go through to -> project -> settings -> Link and add (do not remove the others!) the following libraries to the Object/libary modules line:glut32.lib glu32.lib opengl32.lib glaux.lib
Reference1.Introduction to OpenGL PPT, Presented by Chung-Lin Wen ICG 2006 Fall
2.Interactive Computer Graphics – A Top-Down Approach Using openGL
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