的 Scan-Line Method
[一] 原文書的說法:
To facilitate the search for surfaces crossing a given scan line, an active list of edges is formed for each scan line as it is processed. The active edge list contains only those edges that cross the current scan line, sorted in order of increasing x. In addition, we define a flag for each surface that is set to "on" or "off" to indicate whether a position along a scan line is inside or outside the surface. Pixel positions across each scan line are processed from left to right. This procedure works correctly only if surfaces do not cut through or otherwise cyclically overlap each other. If any kind of cyclic overlap is present in a scene, we can divide the surfaces to eliminate the overlaps.
(擷取部分內容)
[二] 作法
count the minimum and maximum y value of the surface to be drawn (slope of scan lines)
// scan line is a line which parallel to x axis
for each scan line {
calculate the intersections of the boundaries and the scan line
// assume that each surface has only 3 edges so we will get 2 intersections(x1 and x2) at most
// than we draw pixel from (x1, scan line) to (x2, scan line)
for each pixel to be drawn {
calculate the depth (z) of the pixel (x, y) on that surface
if z is smaller than the current depth of that pixel than
draw the pixel with proper color and update the depth
otherwise do nothing.
}
}
[三] depth (z) 的算法
由面積公式可知 Ax + By + Cz + D = 0
得 z = -(Ax + By + D) / C，
下為 A、B、C 和 D 的算法，由平面上三點 (x1, y1, z1), (x2, y2, z2), and (x3, y3, z3) 計算而得
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