Face vertex correction for real-time simulation of a polygon face object

Abstract

The CRT visual system within an aircraft flight simulator receives flight data from a flight simulation computer, and polygon face terrain data from a gaming area data base. The vertices of each polygon face are defined by three object position coordinates. A perspective relationship is maintained between the vertices as the observer changes course in the training flight. The position of each face vertex on the CRT display is determined by two display coordinates. A separate miniraster is constructed for each face based on the position of the vertices. The set of spaced scan lines of progressively increasing and decreasing length thus provided systematically fill in the face area outlined by the face vertices. The vertical position of each vertex will normally not coincide exactly with a scan line, but will fall somewhere between two adjacent scan lines. The endpoint of the scan line subsequent to each vertex must be properly proportioned to accurately position the subsequent edge. The endpoint position is adjusted along the horizontal an amount proportional to the vertical distance from the current vertex to the immediately previous scan line over the entire vertical distance between adjacent scan lines.