Lighting The final color of a pixel in the framebuffer depends partly on the lighting conditions  Lighting can have a major effect on perceived shape of objects                        Topics: Hidden surface removal Controlling lighting in the scene Setting illimination parameters Lighting mathematics

Hidden Surface Removal Three-dimensional applications generally follow the same structure:                     while (1) {    get_viewing_point_from_mouse_position();    glClear(GL_COLOR_BUFFER_BIT);    draw_3d_object_A();    draw_3d_object_B();    draw_3d_object_C();  }   Hidden surface removal is accomplished with a depth buffer Enable depth buffering with glEnable(GL_DEPTH_TEST) Clearing the depth buffer is done with: glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); Hidden line removal is a a little different ...

Real-world and OpenGL Lighting The reflected light which is perceived is a combination of multiple light sources  The surface properties also have a significant effect on the object color   OpenGL simulates the lighting conditions with equasions that: Approximate reality Are easy to implement Software renderers can calculate more realistic calculations Image from http://radsite.lbl.gov/radiance/gallery/image/63b7.jpg

OpenGL Lighting OpenGL lighting comes from a series of light sources which can be turned on or off. In the real world light bounces off surfaces to contribute to the overall illumination  No way to determine source This is simulated in OpenGL by specifying an ambient light  Each surface in the scene has a material definition Specifies reflectivity Some materials can emit light (emmisive) OpenGL lighting model has four parameters: emmisive ambient diffuse specular All four components are computed indepenently and summed

	Ambient, Diffuse, and Specular Light     Ambient illumination is light that's been scattered so much by the environment that its direction is impossible to determine: it seems to come from all directions.(spotlight) Image from http://www.steelcase.com/products/subcategory.html When ambient light strikes a surface it scatters in all directions

	Diffuse Lighting   Diffuse light comes from a single direction Brighter if it strikes a surface directly Scatters equally

	Specular Light Component Specular light is also directional, but scatters in a preferred direction "Shiny materials" have a high specularity Matte materials have low specularity                     The specular, ambient and diffuse components can have different component values (white light in red room - red diffuse component)

	Material Color OpenGL implements object material by specifying the color which an object reflects.  Light and material specification determine the color of an object Lighthouse image from  http://www.midwinter.com/~piaw/gallery/pigeonpointlighthouse.htm    Light also have a diffuse, specular, and ambient color

	Material Color (cont) Diffuse and ambient terms should typically be similiar Specular highlights generally match the light source   Emmissive component adds intensity to the object, but not the overall lighting of the scene. Simulates a self-illuminating object