1. CS380 LAB II OpenGL Donghyuk Kim Reference1. [OpenGL course slides by Rasmus Stenholt] Reference2. [http://nehe.gamedev.net/]http://nehe.gamedev.net/

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

3. Notice Use Noah board for your questions (http://noah.kaist.ac.kr/course/CS380)http://noah.kaist.ac.kr/course/CS380 3

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

5. 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. 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 http://gamedev.stackexchange.com/questions/720 44/why-do-we-use-4x4-matrices-to-transform- things-in-3d

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. 7 void glMatrixMode(GLenum mode);

8. Skeleton Code #include void display(); int main( int argc, char* argv[] ) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA | GLUT_DEPTH); glutInitWindowSize(512, 512); glutCreateWindow("CS380 LAB"); glutDisplayFunc(display); glutMainLoop(); return 0; } void display(){ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glColor3f(1.0,0.0,0.0); glutWireTeapot(0.5); glFlush(); } 8

9. Set a view 9 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); }

10. Set a view 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 glMatrixMode(GL_PROJECTION); glLoadIdentity(); double aspect = width/double(height); gluPerspective(45, aspect, 1, 1024); void gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar);

11. Set a view Detailed explanations about Viewing Transformation will be provided in the next week. 11

12. 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(); glBegin(GL_TRIANGLES); … glEnd(); … 12

13. Draw 3D objects GLUT provide simple 3D objects e.g., Teapot object  void glutSolidTeapot(GLdouble size);  void glutWireTeapot(GLdouble size); 13

14. 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

15. Translations Multiply the current matrix by a translation matrix x, y, z  Specify the x, y, and z coordinates of a translation vector 15 void glTranslatef(GLfloat x,x, y,y, z);

16. Translations Multiply the current matrix by a translation matrix 16 void glTranslatef(GLfloat x,x, y,y, z); 100X 010Y 001Z 0001 Translation matrix (4x4)

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

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

19. Review of Translations glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(0,0,-1.0); 19 1000 0100 0010 0001 Model view matrix

20. Review of Translations glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(0,0,-1.0); 20 1000 0100 0010 0001 Model view matrix 1000 0100 001 0001 1000 0100 001 0001

21. Review of Translations glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(0,0,-1.0); 21 Model view matrix 1000 0100 001 0001 1000 0100 001-2 0001 Again?? 1000 0100 001 0001

22. 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

23. Tutorials Move your teapot based on key inputs  ‘l’: left  ‘r’: right  ‘u’: up  ‘d’: down  ‘f’: move out  ‘n’: move in 23 ‘l’‘f’

24. Tutorials 24 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(); } float xpos = 0.0; float ypos = 0.0; float zpos = -2.0; void main(){ … glutKeyboardFunc(keyboard); … } void display(){ … glTranslatef(xpos,ypos,zpos); … }

25. Rotations 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 void glRotatef(GLfloat angle, GLfloat x,x, y,y, z);

26. Rotations 26 void glRotatef(GLfloat angle, GLfloat x,x, y,y, z); ???0 ???0 ???0 0001 The questions will be resolved in the CS380 lecture “Modeling Transformations“.

27. Rotations void display(){ … glTranslatef(xpos,ypos,zpos); glRotatef(30,0,0,1); … } 27 30 degrees rotation based on a normalized vector (0, 0, 1)

28. Tutorials Rotate your teapot on X axis  e.g., 30, 60, and 90 degrees 28 30 degrees 60 degrees 90 degrees

29. Tutorials 30 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

30. Scaling x, y, z  scale factors along the x, y, and z axes, respectively 30 void glScalef(GLfloat x,x, y,y, z);

31. Scaling 31 void glScalef(GLfloat x,x, y,y, z); X000 0Y00 00Z0 0001

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

33. Review of Scaling 33 void display(){ … glLoadIdentity(); glTranslatef(0,0,-3); glScalef(2,1,1); … } 1000 0100 0010 0001 Model view matrix

34. Review of Scaling 34 void display(){ … glLoadIdentity(); glTranslatef(0,0,-3); glScalef(2,1,1); … } 1000 0100 0010 0001 Model view matrix 1000 0100 001-3 0001 1000 0100 001 0001

35. Review of Scaling 35 void display(){ … glLoadIdentity(); glTranslatef(0,0,-3); glScalef(2,1,1); … } Model view matrix 2000 0100 0010 0001 2000 0100 001-3 0001 1000 0100 001 0001

36. 36 Next time Viewing Transformation in OpenGL