An overview of OpenGL

• A platform independent api
• Designed to work well with both hardware and software
• Standard, open, widely implemented.
• A set of several hundred procedures and functions
• (as well as defined constants.)
• GLU - the OpenGL Utility Library provides additional support functions for modeling.
  • gluOrtho2D allows you to define a 2D viewing frame and is a utility function that uses glOrtho
  • gluOrtho2D( left, right, bottom, top)
  • sets up a two-D viewing region.
  • glOrtho(left, right, bottom, top, near, far)
  • glOrtho(left, right, bottom, top, -1, 1)
  • Specifies the clipping planes for a 3d view volume.
  • See man pages for each.
• GLUT - OpenGL Utility Toolkit, a system independent toolkit for writing OpenGL programs.
  • This is really what is supporting our event driven programs for now
  • It provides interface routines, for example keypress events
  • It also provides some nice routines for creating shapes glutSolidSphere(radius, slices, stacks);
  • Font support as well.
• OpenGL is also thought of as a State Machine
  • You can turn on a light, and it is on until turned off.
  • You tell it the next set of points form a polygon.
• Finally Open Gl is an implementation of the graphics pipeline.
  • 
  • Vertex data is as we have been discussing
  • Pixel data is data from a frame buffer, or image, or ...
  • In a display list data is sent to the display processor once, and does not need to be resent each time the screen is redrawn.
    • Think of this as static local variables in a procedure
    • Use of these can speed up image generation, especially when the network is involved.
  • Evaluators derive actual verticies from given verticies. (Splines, NURBS, ...)
  • Per-Vertex operations turn vertex data into the surfaces.
  • Primitive assembly - clipping and other such operations
  • Pixel operations - pixels are placed in the proper format, and perhaps undergo geometric transformations
  • Rasterization as before,
  • per-Fragment operations - texture mapping, fog, depth buffer, ...