1. Illumination and Shading
Sang Il Park
Sejong University

2. 코딩 연습
Phone Illumination Model을 직접 구현해 본다 (GL_LIGHTING 을 끈 상태로 직접 색을 계산하여 그려본다)
조명을 설정한다. (위치(lx,ly,lz) 및 Intensity)
도형의 색을 설정 (ka, kd, ks)
카메라의 위치 설정 (vx, vy, vz)
그리고 있는 삼각형의 Normal Vector 계산
Phong Model의 각각의 성분 계산 (ambient, diffuse, specular) 계산

3. OpenGL Lighting Functions
Using Illumination/Shading Model:
Turn on/off Lights
glEnable (GL_LIGHTING);
glEnable (GL_LIGHT0);
glEnable (GL_LIGHT1); …
glEnable (GL_LIGHT7);
glDisable (GL_LIGHT0);
glDisable (GL_LIGHT1); …
glDisable (GL_LIGHT7);

4. OpenGL Lighting Functions
glLight * (lightName,lightProperty, propertyValue)
lightName:
GL_LIGHT0, GL_LIGHT1, GL_LIGHT2, …., GL_LIGHT7

5. OpenGL Lighting Functions
Point Light Source:
GLfloat light1pos [] = {2.0, 0.0, 3.0, 1.0};
GLfloat light2pos [] = {0.0, 1.0, 0.0, 0.0};
glLightfv (GL_LIGHT0, GL_POSITION, light1pos);
glEnable (GL_LIGHT0);
glLightfv (GL_LIGHT1, GL_POSITION, light2pos);
glEnable (GL_LIGHT1);
Default value:
GLfloat light0pos [] = {0.0, 0.0, 1.0, 0.0};

6. OpenGL Lighting Functions
Point Light Source Colors:
GLfloat ambientColor[]={0.0,0.0,0.0,1.0};
GLfloat diffuseColor[]={1.0,1.0,1.0,1.0};
GLfloat specularColor[]={1.0,1.0,1.0,1.0};
glLightfv (GL_LIGHT0, GL_AMBIENT, ambientColor);
glLightfv (GL_LIGHT0, GL_DIFFUSE, diffuseColor);
glLightfv (GL_LIGHT0, GL_SPECULAR, specularColor);

7. OpenGL Lighting Functions
Global Light Setting
GLfloat globalAmbient[] = {0.2,0.2,0.2,1.0};
glLightModelfv (GL_LIGHT_MODEL_AMBIENT, globalAmbient);

8. OpenGL Lighting Functions
Point Light Source Attenuation:
glLightf (GL_LIGHT0, GL_CONSTANT_ATTENUATION, );
glLightf (GL_LIGHT0, GL_LINEAR_ATTENUATION, );
glLightf (GL_LIGHT0, GL_QUADRATIC_ATTENUATION, );

9. OpenGL Lighting Functions
Spot Light Source:
Glfloat dirVector [] = {1.0, 0.0, 0.0};
glLightfv (GL_LIGHT0, GL_SPOT_DIRECTION, dirVector);
glLightfv (GL_LIGHT0, GL_SPOT_CUTOFF, 3.0);
glLightfv (GL_LIGHT0, GL_SPOT_EXPONENT, 2.5);

10. OpenGL Material Functions
glMaterial * (surface, sufProperty, propertyValue)
GLfloat diffuseCoeff [] = {0.2,0.4,0.9,1.0};
GLfloat specularCoeff [] ={1.0,1.0,1.0,1.0};
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, diffuseCoeff);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specularCoeff);
glMaterialf (GL_FRONT_AND_BACK, GL_SHININESS, 25.0);

11. OpenGL Material Functions
How to apply some of the properties by glMeterial
glColorMaterial(surface, mode)
surface: GL_FRONT, GL_BACK, GL_FRONT_AND_BACK
mode: GL_EMISSION, GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_AMBIENT_AND_DIFFUSE. ?
glEnable(GL_COLOR_MATERIAL)
VS.
glDisable(GL_COLOR_MATERIAL)

12. OpenGL Lighting Model

13. Tips for a quick lighting setting 1
Set GL_LIGHT_0's position to something like 45 degrees to the 'vertical'. Coordinate (1,1,0) should work nicely in most cases.
Set GL_LIGHT_0's Ambient color to 0,0,0,1
Set GL_LIGHT_0's Diffuse color to 1,1,1,1
Set GL_LIGHT_0's Specular color to 1,1,1,1
Set the glLightModel's global ambient to 0.2,0.2,0.2,1 (this is the default).
Don't set any other glLight or glLightModel options - just let them default.
Enable GL_LIGHTING and GL_LIGHT_0.

14. Tips for a quick lighting setting 1
Enable GL_COLOR_MATERIAL and set glColorMaterial to GL_AMBIENT_AND_DIFFUSE. This means that glMaterial will control the polygon's specular and emission colours and the ambient and diffuse will both be set using glColor.
Set the glMaterial's Specular colour to 1,1,1,1
Set the glMaterial's Emission colour to 0,0,0,1
Set the glColor to whatever colour you want each polygon to basically appear to be. That sets the Ambient and Diffuse to the same value which is what you generally want.

15. Atmospheric Effects
A hazy atmosphere makes colors fade and objects appear dimmer
Hazy-atmosphere effect is often simulated with an exponential attenuation function such as
Higher values for r produce a denser atmosphere

16. A solution for the trackball interface

17. How to use your mouse There is a callback function for mouse in GLUT
Registration:
Implementation
button: GLUT_LEFT_BUTTON, GLUT_RIGHT_BUTTON
action: GLUT_DOWN, GLUT_UP
glutMouseFunc ( myMouse);
void myMouse (GLint button, GLint action,
GLint xpos, GLint ypos );
교재 749page 참조

18. How to Rotate? Virtual trackball
A trackball translates 2D mouse movements into 3D rotations
This is done by projecting the position of the mouse on to an imaginary sphere behind the viewport
As the mouse is moved the camera (or scene) is rotated to keep the same point on the sphere underneath the mouse pointer

19. How to Rotate?
Virtual trackball

20. Review: OpenGL Geometric Transformations
Getting the current matrix value:
glGetFloatv (GL_MODELVIEW_MATRIX, GLfloat elems[16]);
Column major 4 8 12 1 5 9 13 2 6 10 14 3 7 11 15
GLfloat mat [16];
glGetFloatv (GL_MODELVIEW_MATRIX, mat);

21. Review: OpenGL Geometric Transformations
Matrix Direct Manipulation:
glLoadMatrixf(GLfloat elems[16]);
Column major
glMultMatrixf(GLfloat elems[16]);
The current matrix is postmultiplied by the matrix 4 8 12 1 5 9 13 2 6 10 14 3 7 11 15
glLoadIdentity();
glMultMatrixf (M1);
glMultMatrixf (M2);
M = M1∙M2

22. Sang Il Park SEjong University
Ray Tracing
Sang Il Park SEjong University
With lots of slides stolen from Jehee Lee, Doug James, Steve Seitz, Shree Nayar, Alexei Efros, Fredo Durand and others

23. Local vs. Global Illumination Models
Local illumination models
Object illuminations are independent
No light scattering between objects
No real shadows, reflection, transmission
Global illumination models
Ray tracing (highlights, reflection, transmission)
Radiosity (Surface interreflections)
Photon mapping

24. Forward Ray Tracing Rays as paths of photons in world space
Follow photon from light sources to viewer
Problem: Many rays will not contribute to image

25. Backward Ray Tracing Trace rays backward from viewer to light sources
One ray from center of projection through each pixel in image plane
Ray casting
Simplest form of ray tracing
No recursion

26. Backward Ray Tracing Illumination
Phong illumination
Shadow rays
Specular reflection
Specular refraction
Specular reflection and refraction are recursive

27. Shadow Rays Determine if light “really” hits surface point
Cast shadow ray from surface point to light
If shadow ray hits opaque object, no contribution

28. Specular Refraction (Snell’s law)
, : index of refraction of each material
(averaged over wavelengths and temperature)

29. Specular Refraction (Snell’s law)
, : index of refraction of each material
(averaged over wavelengths and temperature)

30. Specular Refraction Path shifts are ignored for thin objects
From Snell’s law, we can obtain the unit transmission vector T in the direction

31. Interpolated transparency
: transmission coefficient
(0 for opaque objects,
1 for totally transparent
objects) 2 1
line of sight

32. Binary Ray-Tracing Tree

33. Ray-surface Intersections
Specialized algorithm for most commonly occurring shapes
Sphere
Polygon
Quadric
Splines
Many shapes are represented in either implicit or parametric form

34. Ray-Implicit Surface Intersections
Parametric ray equation
Initial position
Unit direction vector
Implicit surface
Consists of all points such that
Substitute ray equation for
Solve for s (univariate root finding)

35. Ray-Sphere Intersections
Sphere equation
Substitution
Letting
Solution

36. Ray-Polygon Intersections
Bounding sphere and back face culling is useful
Ray-Plane Intersections
Plane equation containing the polygon
Substitution
Solution
Perform inside-outside test to determine whether the intersection is inside the polygon

37. Acceleration Techniques
Space-subdivision
Uniform subdivision
Adaptive subdivision (Octrees)