Please accept my apology for asking such a simple question. What is the actual meaning of tessellation? Is there any different between tessellation and rasterization? When people say tessellating a polygon, what is he trying to say? Does that mean rasterize a polygon for display? Or, subdividing a polygon? I tried to search with google already. But I couldn't figure out a consistant usage of this vocabulary.

your question made me curious, thanks for asking it. i decided to look in to it and came across the wiki article for it. interesting stuff.

http://en.wikipedia.org/wiki/Tessellation

which lead me to this; http://en.wikipedia.org/wiki/Uniform_tessellation

which then got me to; http://en.wikipedia.org/wiki/Order-4_dodecahedral_honeycomb

and THAT i've seen used in an audio visualization plug-in for winamp called milkdrop, amazing. i'll have to learn how to implement this.

Tessellation refers to breaking down into simpler components. In terms of computer graphics, polygon tesselation or triangulation usually refers to breaking down a complicated (likely concave) polygon into simple triangles.

Rasterization refers to converting shapes defined by their vertices into pixels. So if you are rasterizing a triangle, that means you're taking its vertices coordinates and producing coloured pixels that represent that triangle.

Most graphics card can only render simple triangles, not concave polygons. So if you want to render a concave polygon, you have to tesselate it first into little triangles that make it up. Then the video card can easily render them (by rasterizing them for display, i.e. producing the pixels).

Try looking up the terms on Wikipedia too.