Memoryless artificial horizon generator

Claim 1

In a display apparatus having display face for displaying thereon sky-ground shading and horizon boundary line between said sky and ground shadings, including means for generating sequential raster lines containing sequential pixels and including processor means for providing an initial crossover word representing the point at which said raster line first crosses said horizon boundary line and providing a slope signal based on the slope of said horizon boundary line and further providing a shading signal representing one of said sky or ground shadings wherein the improvement comprises, first digital timing means for providing a first digital signal synchronous with said raster lines; second digital timing means for providing a second digital signal synchronous with said pixels; transition point computing means responsive to said slope signal for providing in real time a current transition point signal representing the intersection of said horizon boundary line with said raster line being currently generated; first comparator means responsive to said current transition point signal and to said second digital signal for providing a left-right signal indicating whether said pixel being currently generated is to the left or to the right of said horizon boundary line; second comparator means responsive to said first digital signal and to said initial crossover word for providing an above-below signal indicating whether said raster line being currently generated is above or below said horizon boundary line; logic means responsive to said left-right signal, said above-below signal, said slope signal, and said shading signal for providing a shading control signal representing either of said sky and ground shadings when said raster line prior to said current transition point is being generated and the other of said shadings when said raster line subsequent to said current transition point is being generated.