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&

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)


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)


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 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


Using homogeneous coordinatesclipping box

homogeneous coordinate:

x/wy/wz/w1


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

http://nehe.gamedev.net/

introduction to opengl & hw1 announcement 劉軒銘, 網媒所 碩二 icg 2012 fall

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introduction to opengl & hw1 announcement 劉軒銘, 網媒所碩二 icg 2012 fall