Introduction to Computer Graphics

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??????? 729441 Chapter 4 Lighting Shading
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Wireframe
?????
????????? ?????????????????????????? (shading
algorithm)
????????? ?????? ?????????
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(No Transcript)
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Rendering

• ????????????? pixel
• ??????????(??? pixel ) ?????????????
• ?????????????????? (normal direction)
• ?????????????????? (luminaires)
• ??????????????????????????????????????
• ????????????????????????????????????

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Rendering Algorithms

• local illumination algorithms
• ?????????????????????????????????????
  ??????????????????????????????????????????
• global illumination algorithms
• ???????????????????????????????????????????

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Local VS Global Illumination
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Local VS Global Illumination
Global
Local
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Scene Geometry
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Radiosity
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Ray-Tracing
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Illumination Variables

• ????????????
• ???????
• ?????????
• ?????
• ??????????????????????
• ?????????????????????????
• ?????????????????????????????????
• surface normal
• ??????????????????? view plane

p0
N
p
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A Model for Lighting

• ???????????????????????????????
• ?????????????????????????????????????????????????
• direct light ????????????????????????????????
• indirect light ???????????????????????????????????
  ??????
• ?????????????????????????????????????????????

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A Model for Lighting

• ????????????
• ?????????????
• ?????????
• ??????????????????
• ???????????????????
• ???????????

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Lighting in Computer Graphics

• ????????? projection plane
• ????????????????????? COP ???????
• projection plane ????????????????????
• ????? pixel ?????????? interaction model

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????????????

• Ambient
• ???????????????????????????????????????????????
  ????????????????????? Why?

???????????????? ???? ??????????????????????
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????????????

• Diffuse
• ????????????????????????????????????????

Specular ?????????????????????????????????
????? ??????????
Emission ????????????????????????????????????
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Interaction Between Light and Materials

• ?? ????????? ????????? ???????????????????????????
  ???????????????????????
• ?????????????????????????????????????????(??????)
  ???????????? ?????????????????????????????
• Shading ?????????????????????????????????

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Material Model

• ???????????????????????????????????????? ????

??????????????????????
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Material Model
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Specular Surfaces

• ????????????????????
• ?????????????????????????????????
• ????? pecfectly specular surface
• ??????????????????????????

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Diffuse Surfaces

• ?????????
• ??????????????????????
• ?????????????????????

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BRDF

• Bi-directional Reflectance Distribution Function
• ????????????????????????????????????

Ideal specular
Ideal diffuse
Rough specular
Directional diffuse
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Illumination Examples
????????????????????specular
?????????????????????(shininess coefficient)
???????????????????? diffuse
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??????????????????????
directional
positional
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?????????????????????

• ???????????????????
• ?????????????????????????????????
• ?????????????????????????
• ??????????????????????????????????????????????????
  ????? ???? ??????????
• ??????????????????
• ???????????????????????????????
• ???????????????????????????????????????????????
• ??????????????????????????????????????????????????
  ??????????????

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?????????????????????

• ??????????????? spot light
• ???????????????????????????
• ??????? spor light

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Shading
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Lighting Models

• illumination model
• surface rendering algorithm

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Shading

• ?????????????????? effect ????????????????????????
  ??????????????
• ??? normal vector ???????????????????????????????
  ?????????????????????

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Example
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Normal Vector
n
p0
p1
p2
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Shading

• Flat Shading
• ???????????????????? normal vector
  ???????????????
• Smooth Shading
• ??????????????????????????????????????????????????
  ???
• ?? 2 ????
• Gouraud Shading
• Phong Shading

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Flat Shading

• Flat Shading
• ???????????????????? normal vector
  ???????????????
• ??????????????????? 1 ??????????
• ????????????????????????????????????

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Gouraud Shading

• Gouraud Shading
• ??????????????????? normal vector ?????????
• ????? interporation ??????????????????????????????
  ???
• ?????????
• ???????????? Flat Shading

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Normal Vector ?????????

• Normal Vector ?????????
• normal vector ????????????????????????????
  ????????????
• ????? normal vector ?????????????????????????
  effect ??????
• ?????????
• ?????????????? normal vector ?????????????????
• ??????????????????

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Phong Shading
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???????????
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Lighting in OpenGL

• ???????????????????? 8 ???
• GL_LIGHT0,GL_LIGHT1,,GL_LIGHT7

glEnable(GL_LIGHTING) glEnable(GL_LIGHT0)
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Lighting in OpenGL
glLightfv()
glLightfiv(GL_LIGHT0, param, value)
GL_AMBIENT GL_DIFFUSE GL_SPECULAR GL_POSITION GL_S
POT_DIRECTION GL_SPOT_EXPONENT GL_SPOT_CUTOFF GL_C
ONSTANT_ATTENTUATION GL_LINEAR_ATTENUATION GL_QUAD
RATIC_ATTENUATION
Light source color intensity
spotlight parameters
irradiance control
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Light Color

• float amb 0.2, 0.2, 0.2. 1.0
• glLightfv(GL_LIGHT0, GL_AMBIENT, amb)

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Light Position
Glfloat position x,y,z,w
1.0f,2.0f,1.0f,1
Glfloat position x,y,z,w
0.0f, 0.0f, 1.0f, 0.0
glLightfv(GL_LIGHT0,GL_POSITION,position)
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glNormal()

• glBegin(GL_QUADS)
• glNormal3f(0,1,0)
• glVertex3f(1,0,-1,0)
• glVertex3f(1,0,1,0)
• glVertex3f(-1,0,1,0)
• glVertex3f(-1,0,-1,0)
• glEnd()

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Shading and OpenGL
glShadeModel(GL_FLAT)
glShadeModel(GL_SMOOTH)
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Material Model

• ????????????????????????????????????????
  

????????????????????????????????? 0?
?????????????????????
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OpenGL Material Properties
glMaterialfv()
glMaterialifv(face, param, value)
GL_FRONT GL_BACK GL_FRONT_AND_BACK
GL_AMBIENT GL_DIFFUSE GL_AMBIENT_AND_DIFFUSE GL_SP
ECULAR GL_EMISSION GL_SHININESS
RGB Values
Phong Exponent
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OpenGL Material Properties
glMaterialfv()
Glfloat mat_ambient 1.0,1.0,1.0,1
glMaterialfv(GL_FRONT,GL_AMBIENT,mat_ambient)
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OpenGL Material Properties
glMaterialfv()
Glfloat mat_diffuse 1.0,1.0,1.0,1
Glfloat mat_specular 0.5,0.4,1.0,1
Glfloat mat_shininess 128.0
glMaterialfv(GL_FRONT,GL_DIFFUSE, mat_diffuse)
glMaterialfv(GL_FRONT,GL_SPECULAR, mat_specular)
glMaterialf(GL_FRONT,GL_SHININESS, mat_shininess)
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Example
(0.0,0.0,1.0,1.0)
(0.0,0.0,4.0,1.0)
(0.0,0.0,2.0,1.0)
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Example
(0.0,0.0,10.0,1.0)
(0.0,0.0,1.0,0.0)
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Example
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Example
????
????
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Example
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(No Transcript)
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Display List

• ????????????????????
• ???????????? memory
• ????????????????????????????? display list
• ???????????????????????????

???????????? Display List

• ?????????????????????????????????
• ?????????? texture ???????????
• ??????????????????????????????? Tree ???

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Display List Model
glBegin(GL_LINES) glVertex() . glEnd()
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???????????? Display List
Gluint glGenLists(int count)

• ????????????????? display list
• ??? ID(????)
• count ??????????? display list
• ???????????????

• Glboolean glIslist(Gluint list)
• ?????????????? list ?????????????????

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?????????? Display List
Glvoid glNewList(Gluinit Listindex,Glenum
Mode) Glvoid glEndList() Listindex ????
display list Mode GLCOMPILE, GLCOMPILE_AND_EXECUT
E
glNewList( 1, GL_COMPILE ) glColor3fv(
colorVector ) glTranslatef( 1.5, 0.0, 0.0
) glBegin( GL_TRIANGLES ) glVertex2f( 0.0, 0.0
) glVertex2f( 1.0, 0.0 ) glVertex2f( 0.0, 1.0
) glEnd() glEndList()
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?? Display List
GLvoid glDeleteLists( GLuint rstIndex, GLsizei
count )
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Example
glNewList( 1, GL_COMPILE ) /????? 1
/ drawFin() glEndList() glNewList( 2,
GL_COMPILE ) / ????? 2 / drawFish() glEndLi
st() glNewList( 3, GL_COMPILE ) / ?????
3(run 1?2/ glCallList( 1 ) glCallList(
2 ) glEndList() glCallList( 3 ) /
drawFin() drawFish() /
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Display List
glNewList( 1, GL_COMPILE ) / define ???? 1
/ drawNewFin() glEndList() glCallList( 3
) / drawNewFin() drawFish() /