1. Reference1. [OpenGL course slides by Rasmus Stenholt]
CS380 LAB II OpenGL
Bochang Moon
Reference1. [OpenGL course slides by Rasmus Stenholt]
Reference2. [

2. Goal Introduce OpenGL programming
Help you do CS380 homework by yourself

3. Notice
Use Noah board for your questions (

4. Outline Transformations Modeling Transformations Draw 3D objects
Translate
Rotate
Scale

5. Transformations
All transformations in OpenGL are carried out by matrices
There are different matrices for different purposes
The modelview matrix
GL_MODELVIEW
The projection matrix
GL_PROJECTION
The texture matrix
GL_TEXTURE
All matrices are post-multiplied
I.e. the current matrix M becomes MN when N is performed
Post-multiplication is closely linked to matrix stacks

6. Transformations Matrices All matrices in OpenGL are 4x4
Why use 4-D matrices for 3-D graphics?
A 4x4 matrix can rotate and translate the same vector in one operation
A 4x4 matrix can make the otherwise non-linear perspective projection linear
Modern CPUs are very efficient at handling 4x4 matrices

7. Transformations Specify which matrix is the current matrix Mode
GL_MODELVIEW
Applies subsequent matrix operations to the model view matrix stack
GL_PROJECTION
Applies subsequent matrix operations to the projection matrix stack
etc.
void glMatrixMode(
GLenum  
mode);

8. Set a view int main( int argc, char* argv[] ){ …
glutReshapeFunc( reshape ); }
void reshape(int width, int height) {
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
double aspect = width/double(height);
gluPerspective(45, aspect, 1, 1024); }

9. Set a view fovy aspect zNear zFar
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
double aspect = width/double(height);
gluPerspective(45, aspect, 1, 1024);
void gluPerspective(
GLdouble  
fovy,
aspect,
zNear,
zFar);
fovy
View angle, in degrees, in the y direction
aspect
Ratio of x (width) to y (height)
zNear
Distance from the viewer to the near clipping plane (positive)
zFar
Distance from the viewer to the far clipping plane (positive)

10. Set a view
Detailed explanations about Viewing Transformation will be provided in the next week.

11. Draw 3D objects Use a set of OpenGL primitives e.g.,
glBegin(GL_TRIANGLES);
glVertex3f( 0.0f, 1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd(); …

12. Draw 3D objects GLUT provide simple 3D objects e.g., Teapot object
void glutSolidTeapot(GLdouble size);
void glutWireTeapot(GLdouble size);

13. Draw 3D objects void display(){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0);
glColor3f(r,g,b);
glutWireTeapot(0.5);
glFlush(); }

14. Translations Multiply the current matrix by a translation matrix
x, y, z
Specify the x, y, and z coordinates of a translation vector
void glTranslatef(
GLfloat   x, y,
z);

15. Translations Multiply the current matrix by a translation matrix
void glTranslatef(
GLfloat   x, y,
z);
Translation matrix (4x4) 1 X Y Z

16. Review of Translations
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0);

17. Review of Translations
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0);
Model view matrix

18. Review of Translations
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0); 1
Model view matrix

19. Review of Translations
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0); 1 1 -1 1 -1
Model view matrix

20. Review of Translations
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0);
Again?? 1 -1 1 -1 1 -2
Model view matrix

21. Review of Translations
void display(){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-1.0);
glColor3f(r,g,b);
glutWireTeapot(0.5);
glFlush(); }

22. Tutorials Move your teapot based on key inputs ‘l’: left ‘r’: right
‘u’: up
‘d’: down
‘f’: move out
‘n’: move in
‘l’
‘f’

23. Tutorials float xpos = 0.0; float ypos = 0.0; float zpos = -2.0;
void keyboard(unsigned char key, int x, int y){
if (key == 'l')
xpos -= 0.1;
else if (key == 'r')
xpos += 0.1;
else if (key == 'u')
ypos += 0.1;
else if (key == 'd')
ypos -= 0.1;
else if (key == 'f')
zpos -= 0.1;
else if (key == 'n')
zpos += 0.1;
glutPostRedisplay(); }
void display(){ …
glTranslatef(xpos,ypos,zpos); }

24. Rotations angle x, y, z angle of rotation, in degrees
void glRotatef(
GLfloat  
angle, x, y,
z);
angle
angle of rotation, in degrees
x, y, z
x, y, and z coordinates of a vector, respectively
Normalized vector (If not, GL will normalize it)

25. Rotations void glRotatef( GLfloat angle, x, y, z); ? 1x, y,
z); ? 1
The questions will be resolved in the CS380 lecture “Modeling Transformations“.

26. Rotations void display(){ … glTranslatef(xpos,ypos,zpos);
glRotatef(30,0,0,1); }
30 degrees rotation based on a normalized vector (0, 0, 1)

27. Tutorials Rotate your teapot on X axis e.g., 30, 60, and 90 degrees

28. Tutorials 30 degrees on X axis 60 degrees on X axis
glRotatef(30,1,0,0);
60 degrees on X axis
glRotatef(60,1,0,0);
90 degrees on X axis
glRotatef(90,1,0,0);

29. Scaling x, y, z scale factors along the x, y, and z axes, respectively
void glScalef(
GLfloat   x, y,
z);

30. Scaling
void glScalef(
GLfloat   x, y,
z); X Y Z 1

31. Scaling void display(){ … glLoadIdentity(); glTranslatef(0,0,-3);
glScalef(2,1,1); }

32. Review of Scaling void display(){ 1 … glLoadIdentity();
glTranslatef(0,0,-3);
glScalef(2,1,1); } 1
Model view matrix

33. Review of Scaling void display(){ … glLoadIdentity();
glTranslatef(0,0,-3);
glScalef(2,1,1); } 1 1 -3 1 -3
Model view matrix

34. Review of Scaling void display(){ … glLoadIdentity();
glTranslatef(0,0,-3);
glScalef(2,1,1); } 1 -3 2 1 2 1 -3
Model view matrix

35. Questions Why use 4-D matrices for 3-D graphics?
Combine multiple transformations into a 4x4 matrix 1 -3 2 1 2 1 -3
Model view matrix

36. Next time
Viewing Transformation in OpenGL