API provides building blocks and routines for developing software applications consistently across operating systems. Direct3D and OpenGL are 3D graphics APIs that make it easier for developers to create 3D graphics. The graphics pipeline is the stages required to transform 3D images into 2D for display, processing vertex properties like position and color through stages like assembly, lighting and rendering for output.

1. HA4 – Displaying 3D polygon animations
API
API, an abbreviation of application program interface, is a set of routines, protocols, and tools for
building software applications. A good API makes it easier to develop a program by providing all the
building blocks. A programmer then puts the blocks together. Most operating environments, such as
MS-Windows, provide an API so that programmers can write applications consistent with the
operating environment. Although APIs are designed for programmers, they are ultimately good for
users because they guarantee that all programs using a common API will have similar interfaces. This
makes it easier for users to learn new programs.http://www.webopedia.com/TERM/A/API.html
Direct3D
Direct3D is an application program interface (API) developed by Microsoft that provides a set of
commands and functions for manipulating 3D objects. By using Direct3D commands, software
developers can take advantage of many prewritten functions. This allows programmers to write
significantly less code than if they had to write all the functions from scratch. Direct3D makes it
relatively easy to manage three-dimensional objects, including lighting and shadows as well. In order
for a software program to use Direct3D commands, the computer's video card or graphics
accelerator device must support Direct3D. Fortunately, just about all video cards made for PCs offer
Direct3D support. While many video games and other programs use Direct3D, OpenGL is a more
widely used standard.http://www.techterms.com/definition/direct3d
OpenGL
OpenGL, or the Open Graphics Library, is a 3D graphics language developed by Silicon Graphics.
Before OpenGL was available, software developers had to write unique 3D graphics code for each
operating system platform as well as different graphics hardware. However, with OpenGL,
developers can create graphics and special effects that will appear nearly identical on any operating
system and any hardware that supports OpenGL. This makes it much easier for developers of 3D
games and programs to port their software to multiple platforms.
So how exactly does OpenGL work? When programmers write OpenGL code, they specify a set of
commands. Each command executes a drawing action or creates a special effect. Using hundreds or
even thousands of these OpenGL commands, programmers can create 3D worlds which can include
special effects such as texture mapping, transparency (alpha blending), hidden surface removal,
antialiasing, fog, and lighting effects. An unlimited amount of viewing and modelling transformations
can be applied to the OpenGL objects, giving developers an infinite amount of
possibilities.http://www.techterms.com/definition/opengl
Graphics Pipeline
In 3D graphics rendering, the stages required to transform a three-dimensional image into a two-
dimensional screen. The stages are responsible for processing information initially provided just as
properties at the end points (vertices) or control points of the geometric primitives used to describe
what is to be rendered. The typical primitives in 3D graphics are lines and triangles. The types of

2. properties provided per vertex include x-y-z coordinates, RGB values, translucency, texture,
reflectivity and other characteristics.
An Assembly Line
Graphics rendering is like a manufacturing assembly line with each stage adding something to the
previous one. Within a graphics processor, all stages are working in parallel. Because of this pipeline
architecture, today's graphics processing units (GPUs) perform billions of geometry calculations per
second. They are increasingly designed with more memory and more stages, so that more data can
be worked on at the same time.
The Goal
For gamers, photorealistic rendering at full speed is the goal, and human skin and facial expressions
are the most difficult. Although there are always faster adapters on the market with more memory
and advanced circuitry that render 3D action more realistically, thus far, no game has fooled anyone
into believing a real person is on screen, except perhaps for a few seconds. If you wish to read more,
go to the link below.
http://www.pcmag.com/encyclopedia/term/43933/graphics-pipeline