Hardware implementation of clipping and intercoordinate comparison logic

In a graphics display system for displaying an object defined by a plurality of objects coordinates, said system utilizing a clip window defined by a plurality of clip coordinates for clipping said object prior to display, and a test window defined by a plurality of predetermined offsets from said clip coordinates for operating in conjunction with said clip window to selectively determine whether said object should be clipped in accordance with a first method of clipping or a second method of clipping, an apparatus for facilitating the clipping and rendering of said object comprising:

• a plurality of coordinate registers for storing said object coordinates;
• a plurality of clip coordinate registers for storing said clip coordinates;
• a plurality of offset registers for storing said predetermined offsets;
• a plurality of multiplexers coupled to said plurality of object coordinate registers, said plurality of clip coordinate registers, and said plurality of offset registers, for selectively outputting predetermined object coordinates, clip coordinates, and predetermined offsets;
• a plurality of comparators coupled to said plurality of multiplexers for comparing said selectively output predetermined object coordinates, clip coordinates, and predetermined offsets;
• a plurality of incrementor/decrementors coupled to said plurality of clip coordinate registers and said plurality of offset registers for calculating the borders of said test window relative to the borders of said clip window;
• and
• means for clipping and rendering said object based upon a plurality of output signals from said plurality of comparators in accordance with said borders of said test window relative to the borders of said clip window.

In a graphics display system for displaying an object defined by a plurality of object coordinates, said system including at least one object coordinate register, at least one clip coordinate register, at least one offset register, at least one multiplexer coupled to said at least one object coordinate register, said at least one clip coordinate register and said at least one offset register, at least one comparator coupled to said at least one multiplexer, and incrementor/decrementors means coupled to said plurality of clip coordinate registers and said plurality of offset registers, said system utilizing a clip window defined by a plurality of clip coordinates for clipping said object prior to display, and a test window defined by a plurality of predetermined offsets from said clip coordinates for operating in conjunction with said clip window, a method for clipping and rendering said object using said clip window, said method comprising the steps of:

• storing said at least one object coordinate in said at least one object coordinate register;
• storing at least one clip coordinate in said at least one clip coordinate register;
• storing said predetermined offsets in at least one offset register;
• selectively outputting predetermined object coordinates, clip coordinates, and predetermined offsets from said at least one multiplexer;
• comparing said selectively output predetermined object coordinates, clip coordinates, and predetermined offsets in said at least one comparator so as to generate a plurality of output signals;
• calculating the borders of said test window relative to the borders of said clip window in said incrementor/decrementor means;
• and
• utilizing said plurality of comparator output signals and said at least one incrementor/decrementor to determine whether to clip said object prior to displaying said object, such that in the event that said comparator output signals indicate that portions of said object are outside of said clip window, said portions of said object are clipped before rendering said object.