Rendering  Illuminated Objects To render lit surfaces OpenGL must: Define normal vectors for each vertex of all the objects  Create, select, and position one or more light sources.  Create and select a lighting model Define material properties for the objects  (walk through code)     Programming Notes: Make sure each light is enabled after defining Make sure lighting is enabled Changes in lighting may be utilized with display lists for potential performance inprovements.

	Creating light souces Fin 2   void glLight{if}(GLenum light, GLenum pname, TYPE param);  void glLight{if}v(GLenum light, GLenum pname, TYPE *param);  Creates the light specified by light, which can be GL_LIGHT0, GL_LIGHT1, ... , or GL_LIGHT7.

	Lighting Parameters   NOTE!  Default values of GL_DIFFUSE and GL_SPECULAR apply only to GL_LIGHT0 (0.0, 0.0, 0.0, 1.0) for the other lights

Specifying the position and color of a light    GLfloat light_ambient[] = { 0.0, 0.0, 0.0, 1.0 };  GLfloat light_diffuse[] = { 1.0, 1.0, 1.0, 1.0 };  GLfloat light_specular[] = { 1.0, 1.0, 1.0, 1.0 }; GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };  glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);  glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);  glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);  glLightfv(GL_LIGHT0, GL_POSITION, light_position); Note: Remember to turn on each light with glEnable(). (See "Enabling Lighting" for more information about how to do this.)

	Color GL_DIFFUSE color correlates to the "typical" color of a light\ Defines the color and intensity that a light adds to the scene  GL_SPECULAR color defines what color specular highlights will be (picture of angular reflectivity)

Position and Attenuation Lights can be considered directional or positional Rays of directional lights can be considered to be parallel The sun is an example of a real-world directional light  GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };  glLightfv(GL_LIGHT0, GL_POSITION, light_position); The light position is defined as (x, y, z, w) w  = 0.0:    (x, y, z) = light direction w  != 0.0:   (x, y, z) = light position          By Default GL_POSITION = {0, 0, 1, 0} (directional, along the -Z axis) Positional lights radiate in all directions by default may be defined as spotlights

	Programming Note: Large Polygons with local (positional) lights will interpolate the light values across the polygon A problem for LARGE polygons (they may appear darker) Break the polygon into smaller polygonal pieces

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