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7.4. Scan Conversion or Rasterization 157
value for the second polygon can be assigned to that fragment and the associ-
ated 3D x-coordinate will be updated. Otherwise, the current attributes will
remain unchanged. This procedure determines which polygon is visible from
the viewpoint. Remember, we have defined the viewing plane to be at x = 1.
Therefore, the 3D x-coordinate of each vertex determines how far it is from
the viewing plane. The closer it is to the viewing plane, the more likely that
the object connected to that vertex will not be occluded by other objects in
the scene. Essentially, this procedure is carried out by the Z-buffer