Lights and Materials

1
Lights and Materials

• OpenGL Part II

2
Light Properties

• The amount of light at one pixel is determined
  by
• Specular
• Diffuse
• Ambient
• Emit
• Both the materials and the lights have this
  property!
• Interaction between the two is what determines
  the color
• Its a way of faking physically realistic lights

3
OpenGL

• OpenGL has point lights and directional lights
• By default, OpenGL scenes have no light
• The number of lights is hardware dependent
  (typically a minimum of 8)

4
Getting things going

• First, enable lighting
• glEnable (GL_LIGHTING)
• This disables any colors from glColor()!
• Turn on the individual lights
• glEnable (GL_LIGHT0)
• Setup light position and properties

5
Basic Light Source

• // Setup light position
• GLfloat light_position 100.0f, 100.0f,
  100.0f, 0.0f
• glLightfv (GL_LIGHT0, GL_POSITION,
  light_position)
• // Setup diffuse property
• GLfloat diffuse_light 0.9f, 0.9f, 0.9f,
  0.0f
• glLightfv (GL_LIGHT0, GL_DIFFUSE, diffuse_light)
• // Setup ambient property
• GLfloat ambient_light 0.2f, 0.2f, 0.2f,
  0.0f
• glLightfv (GL_LIGHT0, GL_AMBIENT, ambient_light)
• // Setup specular property
• GLfloat specular_light 0.5f, 0.5f, 0.5f,
  0.0f
• glLightfv (GL_LIGHT0, GL_SPECULAR,
  specular_light)
• Note the v is for vector

NOTE! If this is a 0, then itis
locatedinfinitelyfar away!The lightis now
adirectionallight! (i.e. a sun)
6
A function

• void setupLights()
• glEnable (GL_LIGHTING)
• glEnable (GL_LIGHT0)
• glLightfv (GL_LIGHT0, GL_POSITION,
  light_position)
• glLightfv (GL_LIGHT0, GL_DIFFUSE,
  diffuse_light)
• glLightfv (GL_LIGHT0, GL_AMBIENT,
  ambient_light)
• glLightfv (GL_LIGHT0, GL_SPECULAR,
  specular_light)
• glLightfv (GL_LIGHT0, GL_EMISSION,
  emission_light)

7
Spot Lights

• Still specify all that other stuff
• Make sure its 4th position is not 0
• Use glLightfv to specify other properties
• // Direction of light
• glLightfv (GL_LIGHT0, GL_SPOT_DIRECTION,
  spot_dir)
• // size of cone
• glLightfv (GL_LIGHT0, GL_SPOT_CUTOFF, 1.2f)
• // amount of dropoff
• glLightfv (GL_LIGHT0, GL_SPOT_EXPONENT, 20.0f)
• // quadratic, linear and constant dropoff
• glLightfv (GL_LIGHT0, GL_QUADRATIC_ATTENUATION,
  0.0f)
• glLightfv (GL_LIGHT0, GL_LINEAR_ATTENUATION,
  0.0f)
• glLightfv (GL_LIGHT0, GL_CONSTANT_ATTENUATION,
  1.0f)

8
Rotating a Light Source

• void display()
• glClear (GL_COLOR_BUFFER_BITGL_DEPTH_BUFFER_BIT)
  
• glMatrixMode(GL_MODELVIEW)
• glPushMatrix()
• glLoadIdentity()
• glTranslatef(0.0, 0.0, -5.0)
• glRotatef (deg, 0.0, 1.0, 0.0)
• glLightfv (GL_LIGHT0, GL_POSITION,
  light_position)
• glutSolidTeapot(1.0)
• glPopMatrix()
• glutSwapBuffers()
• glFlush()

9
Summary on Lights

• Must specify
• Must enable lighting and individual lights
• Ambient, diffuse, specular, emit
• If 4th element in light position is 0, its a sun
• A point light can become a spotlight
• Light properties interact with materials

10
Materials(not textures)

• Materials define the color of
• Diffuse
• Specular
• Ambient
• Specular
• Also define the amount of shininess
• Must specify the material each time before
  drawing!

11
Example brass

• GLfloat brass_ambient0.33, 0.22, 0.03, 1.0
• GLfloat brass_diffuse0.78, 0.57, 0.11, 1.0
• GLfloat brass_specular0.99, 0.91, 0.81, 1.0
• GLfloat brass_shininess 27.8
• glMaterialfv(GL_FRONT, GL_AMBIENT,
  brass_ambient)
• glMaterialfv(GL_FRONT, GL_DIFFUSE,
  brass_diffuse)
• glMaterialfv(GL_FRONT, GL_SPECULAR,
  brass_specular)
• glMaterialf(GL_FRONT, GL_SHININESS,
  brass_shininess)

12
Output
13
Defining a Materials Structure

• typedef struct materialStruct
• GLfloat ambient4
• GLfloat diffuse4
• GLfloat specular4
• GLfloat shiniess
• materialStruct brass
• 0.33, 0.22, 0.03, 1.0,
• 0.78, 0.57, 0.11, 1.0,
• 0.99, 0.91, 0.81, 1.0,
• 27.8
• glMaterialfv(GL_FRONT, GL_AMBIENT,
  brass-gtambient)

14
teapots.c

• http//www.opengl.org/resources/code/basics/redboo
  k/

15
materials.c

• http//www.opengl.org/resources/code/basics/redboo
  k/