Active-Edge Table
The active-edge table is a data structure that consists of all the intersection points of the edges with the current scanline. These intersection points are sorted by increasing x coordinate. This allows the intersection points to be paired off, and be used for filling the scanline appropriately.
As the scan conversion moves on to the next scanline, the AET is updated so that it properly represents that scanline.
The above figure shows the AET for scanline 8.
As can be seen above, line segments that are drawn between two points lying inside the polygons, do not always lie inside the polygon. These polygons are classified as concave polygons.
Convex Polygons
A polygon is defined to be convex if for any two points that lie within the polygon, the line segment connecting them is also inside the polygon.
Given below are a few examples of convex polygons:
The edge table is an array of pointers to linked lists, as shown in the figure. It has one row for each scanline, and each element of the array points to a linked list of edges whose minimum y coordinate lies on that edge. For example, in the figure, scanline 5 would contain edge CD since CD's minimum y coordinate lies on scanline 5.
The actual data stored about each edge is implementation dependent, but one such implementation could be as shown:
A polygon is a many-sided planar figure composed of verticies and edges.Rectangles, triangles, squares, are all examples of polygons. For the purpose of this tutorial, we will classify polygons into two mutually exclusive types:
A primitive, in the context of computer graphics, is defined to be any fundamental mathematical construct that is used as a basis for building other figures. Lines, squares, circles, rectangles, etc are all considered to be primitives.
A raster scan display is a display which stores the display primitives in a refresh buffer in terms of their component pixels. The complete image on a raster display is formed from a raster which is a set of horizontal scan lines, each a row of individual pixels.
From Graphica -- see details 26.11.1996