OpenGL_ModelingScene.pptx

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Modeling with OpenGL

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Intent

 Learn OpenGL matrix operations  Model a 3D world

◦ Use quads, lines, triangles,cubes, spheres and other primitives

◦ Apply Color

◦ Translation, Rotation, Scale

◦ OpenGL stae machine, saving state, restoring

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Setting up OpenGL for MS VC++

Copy & Paste :

 glut32.dll to %WinDir%\System,

 glut32.lib to $(MSDevDir)\..\..\

VC98\lib, and

 glut.h to $(MSDevDir)\..\..\VC98\

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Setting up for MS VC++

2008

Copy & Paste :

 glut32.dll to %WinDir%\System,

 glut32.lib to

..\Program Files\Microsoft Visual Studio 9.0\VC\lib

and

 glut.h to ..\Program Files\Microsoft

Visual Studio 9.0\include\GL.

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Beginning

 Open Visual Studio

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Adding OpenGL Codes

#include<windows.h> #include<cstdio>

#include<cmath>

#include<GL/glut.h>

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Adding OpenGL code

int main(int argc, char **argv) {

glutInit(&argc,argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (900,900);

glutInitWindowPosition (0, 0); glutCreateWindow("Hello 3D"); init(); // init display modes

glutDisplayFunc(display); // display update glutMainLoop();

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Adding OpenGL code

Write init(), display() functions

void display() {

glClear(GL_COLOR_BUFFER_BIT);

// …..

// write display codes … // …….

glFlush(); // update display

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Init()

void init(void) {

glClearColor(0.0,0.0,0.0,0.0); // black color

//set up projection mode

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Now, what to do ?

 Add some models  Add Camera

 Add Projection

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Add some models

 Hand-sketch or draw a story

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Add some models

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Add some models

 Suppose this is our world

A field of 30X30

size

A c_ub e cen

tere d a_t (5,1

,5)

This stru_cture

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Add the field

void display() {

glClear(GL_COLOR_BUFFER_BIT); // …..

// write display codes …

glMatrixMode(GL_MODELVIEW); glColor3f(1.0,1.0,1.0); //white glBegin(GL_LINE_LOOP); glVertex3f(-15.0,0.0,15.0); glVertex3f(15.0,0.0,15.0); glVertex3f(15.0,0.0,-15.0); glVertex3f(-15.0,0.0,-15.0); glEnd(); // …….

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Add the cube

void display()

{

glClear(GL_COLOR_BUFFER_BIT); // …..

// write display codes … glMatrixMode(GL_MODELVIEW); glColor3f(1.0,1.0,1.0); //white glBegin(GL_LINE_LOOP); glVertex3f(-15.0,0.0,15.0); glVertex3f(15.0,0.0,15.0); glVertex3f(15.0,0.0,-15.0); glVertex3f(-15.0,0.0,-15.0); glEnd(); glTranslated(5.0,1.0,5.0); glutWireCube(1.0); // …….

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What about viewing ?

 Want to view what we have done

so far

 Press Ctrl + F5

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What about viewing ?

 What do you find ?

◦ Nothing

◦ Whats the problem ?

 No view !!

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Add a view

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Add a view

glMatrixMode(GL_MODELVIEW); glLoadIdentity();

gluLookAt(

??

);

 _{From where we are looking at ?}

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Add a view

 It seems we are looking at the

origin (0,0,0) from a bit distant… and high

 Say, eye position at

(25,25,-25)

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Add a view

gluLookAt(

25.0,25.0,-25.0, 0.0,0.0,0.0,

0.0,1.0,0.0

);

Should we be able to get some output if we run

now ?

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Add Projection

Add projection

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Now Run

 Ctrl + F5

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Adding the axes

glColor3f(0.3,0.3,0.3); glBegin(GL_LINES);

glVertex3f(0.0,0.0,-15.0); glVertex3f(0.0,0.0,15.0); glEnd();

glBegin(GL_LINES);

glVertex3f(-15.0,0.0,0.0); glVertex3f(15.0,0.0,0.0);

glEnd();

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Adding a grid

glMatrixMode(GL_MODELVIEW); glColor3f(0.3,0.3,0.3); #define EXTX 14

#define EXTZ 14

double x = -(double)EXTX;

for(int i = 1; i<=2*EXTX+1; i++) glVertex3f(x,0.0,-15.0); glVertex3f(x,0.0,15.0); x += 1.0;

} glEnd();

double z = -(double)EXTZ;

for(int i = 1; i<=2*EXTZ+1; i++) {

glVertex3f(-15.0,0.0,z); glVertex3f(15.0,0.0,z); z += 1.0;

} glEnd();

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What about moving the

camera

 ;-)

 It looks like a film storyboard  Let us animate the camera

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Moving the camera

 Enable double buffer and add a mouse

function

int main(int argc, char **argv) {

glutInit(&argc,argv);

glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutInitWindowSize (900,900);

glutInitWindowPosition (0, 0); glutCreateWindow("Hello 3D"); init(); // init display modes

glutDisplayFunc(display); // display update glutMouseFunc(mouse);

glutMainLoop(); return 0;

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Moving the camera

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Moving the camera

 SpinDisplay will be called whenever

idle

 Add a global variable camera_angle

 Write the spinDisplay() function to

update camera angle

void spinDisplay(void) {

camera_angle = camera_angle + 0.2; if(camera_angle > 360.0)

camera_angle = camera_angle - 360.0;

glutPostRedisplay();

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Change the camera code

 Add a circle equation for camera

#define PI 3.1415926535897932

double eyex = 25.0*cos(camera_angle*PI/180.0); double eyez = 25.0*sin(camera_angle*PI/180.0);

gluLookAt(

eyex,25.0,-eyez,

0.0,0.0,0.0, 0.0,1.0,0.0 );

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Moving the camera

 Run it …

 Click the mouse

 Check that the camera is moving

◦ Don’t be confused, here model is static

◦ Only camera is moving

 Later we will do things, where

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Adding one more model

 Intent it

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Adding one more model

void drawHighTriangle() {

glBegin(GL_LINE_LOOP); glVertex3f(0.0,0.0,0.0); glVertex3f(0.0,1.0,0.0); glVertex3f(1.0,0.0,0.0); glEnd();

glBegin(GL_LINE_LOOP); glVertex3f(0.0,0.0,0.0); glVertex3f(0.0,1.0,0.0); glVertex3f(0.0,0.0,1.0); glEnd();

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Adding one more model

 Now, we want to draw this model

at (-8,0,8) with 5X scaling

 Should this work ?

glTranslated(-8.0,0.0,8.0); glScalef(5.0,5.0,5.0);

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Adding one more model

 Say we have one cube at (5,1,5)

 Say we draw the cube by :

glTranslated(5.0,1.0,5.0); glutWireCube(1.0);

 Now, how to draw the other model ??

glTranslated(-8.0,0.0,8.0); glScalef(5.0,5.0,5.0);

drawHighTriangle();

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Order Matters ?

glColor3f(0.0,1.0,1.0);

glTranslated(-8.0,0.0,8.0); glScalef(5.0,5.0,5.0);

drawHighTriangle();

glColor3f(1.0,1.0,0.0);

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Order Matters ?

glColor3f(1.0,1.0,0.0);

glTranslated(5.0,1.0,5.0); glutWireCube(5.0);

glColor3f(0.0,1.0,1.0);

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More..

 And if there is rotation …

glColor3f(0.0,1.0,1.0);

glRotatef(25.0,0.0,0.0,1.0); drawHighTriangle();

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More..

 And if there is rotation …

glColor3f(1.0,1.0,0.0); glTranslated(5.0,1.0,5.0); glRotatef(45.0,1.0,0.0,0.0); glutWireCube(5.0);

glColor3f(0.0,1.0,1.0);

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Why this happens ?

OpenGL is a state machine. Proper process ?

glPushMatrix();

glColor3f(1.0,1.0,0.0); glTranslated(5.0,1.0,5.0); glutWireCube(5.0);

glPopMatrix();

glPushMatrix();

glColor3f(0.0,1.0,1.0); glTranslated(-8.0,0.0,8.0); glScalef(5.0,5.0,5.0);

drawHighTriangle();

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Transformation in OpenGL

 _{OpenGL uses 3 stacks to maintain} transformation matrices:

 Model & View transformation matrix stack  Projection matrix stack

 Texture matrix stack

 You can load, push and pop the stack

 _{The top most matrix from each stack is applied to}

all graphics primitive until it is changed

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Translation – 2D

(4,5) (7,5) Y X Before Translation                                                             1 * 1 0 0 1 0 0 1 1 y x d d y x T P P d d T y x P y x P y x y x Form s Homogeniou

x’ = x + d_x y’ = y + d_y

(7,1) (10,1)

X Y

Translation by (3,-4)

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Transformations and OpenGL

®

 _{Each time an OpenGL transformation}_M is called the current MODELVIEW matrix

C is altered:

Cv

v  v  CMv

glTranslatef(1.5, 0.0, 0.0); glRotatef(45.0, 0.0, 0.0, 1.0);

CTRv v 

Note: v is any vertex placed in rendering pipeline v’ is the transformed vertex from v.

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Order of Transformations

 T: Translate 20 unit along X

 _{glTranslatef(20.0, 0.0, 0.0);}

 R1 : Rotate 90 degree around X

 _{glRotatef(90,0, 1.0, 0.0, 0.0);}

 T2: Translate 10 unit along Y

 _{glTranslatef(10.0,0.0,1.0, 0.0);}

 _{This translation is actually along the}

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Saving the state

 _{Transformations have cumulative effect}  _{glPushMatrix() saves present state}

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So how to draw models

 When we know the position of

things around a special

orientation/ reference point we

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Thinking About Transformations

As a Global System

 _{Objects moves but}

coordinates stay the same

 _Think_of

transformation in

reverse order as

they appear in code

As a Local System

 _{Objects moves and}

coordinates move with it

 _Think_of

transformation in

same order as they

appear in code _{There is a World Coordinate System where:}

 _{All objects are defined}

 _{Transformations are in World Coordinate space}

Two Different Views

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Local View

 Translate Object  _Then_Rotate

Order of Transformation T•R

glLoadIdentity();

glMultiMatrixf( T);

glMultiMatrixf( R);

draw_ the_ object( v); v’ = ITRv

Global View

 Rotate Object  _Then_Translate

Effect is same, but perception is different

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glLoadIdentity();

glMultiMatrixf( R);

glMultiMatrixf( T);

draw_ the_ object( v); v’ = ITRv

Local View

 _Rotate_Object  _Then_Translate

Global View

 _Translate_Object  _Then_Rotate

Effect is same, but perception is different

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Animating Models

 Previously we animated camera  Now we animate models

 Straight forward process

◦ Enable double buffering ◦ Keep an IdleFunction

◦ Update animation data inside idle function

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Animating models

glPushMatrix();

glColor3f(1.0,1.0,0.0); glTranslated(5.0,1.0,5.0);

glRotatef(angle_1,1.0,0.0,0.0); glutWireCube(5.0); glPopMatrix(); glPushMatrix(); glColor3f(0.0,1.0,1.0); glTranslated(-8.0,0.0,8.0); glScalef(5.0,5.0,5.0);

glRotatef(angle_2,0.0,0.0,1.0); drawHighTriangle();

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Animating models

 Inside the idleFunction (here spinDisplay) update

animation data

void spinDisplay(void) {

camera_angle = camera_angle + 1.0;

angle_1 += 2.0; angle_3 += 5.0;

if(camera_angle > 360.0)

camera_angle = camera_angle - 360.0;

if(angle_1 > 360.0)

angle_1 = angle_1 - 360.0; if(angle_2 > 360.0)

angle_2 = angle_2 - 360.0;

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