The Vertex Shader :

A vertex shader handles small programs or instruction sets and applies them to each vertex received through the geometry processing line. ATi's vertex shader is able to accept upto 16 individual data streams for each vertex (the grey boxes 0 to 15 at the top). This data may include positional coordinates, texture coordinates,lighting values, weighting values for matrix skinning, or anything else the developer desires. A vertex shader program can have a maximum length of 128 instructions, and make use of up to 96 constant values and 12 temporary data registers allowing for an almost unprecedented level of flexibility to create a mind numbing range of effects limited only by the programers ability and imagination.

Vertex Shader Uses:

From realistic, shimmering and deforming soap bubbles to the example below where a cloth is draped over a sphere, the vertex shader open up a huge box of tricks to the developer.

Vertex shaders also allow for the effective creation of volumetric shadows which serve to add depth and mood to scene as can be seen below.

Some other effects ATi suggest are suited to vertex shader routines include, but are not restricted to :

• Fur Rendering – grow realistic fur from any object that can be made to curl or blow in the
  wind if desired.
• Particle Systems – animate large numbers of small particles by assigning and modifying
  physical properties such as mass, velocity, acceleration, etc. Useful for modeling fire,
  sparks, explosions, smoke, rain, snow, and more.
• Lens Effects – distort an image as if it were being viewed through a lens.
• Matrix Palette Skinning – allow skeletally animated characters with many bones to move
  freely and bend naturally.
• Advanced Keyframe Interpolation – perform animation and morphing effects using non-linear
  blending between two or more keyframes. Useful for modeling complex facial
  expressions and speech.

Page 4 - The Pixel Shader