Apparatus and method for relating a point of selection to an object in a graphics display system

A video display system for picking visible objects from rendered three dimensional objects, comprising:

• a frame buffer for storing displayed image data of rendered three dimensional objects;
• a Z buffer memory for storing displayed image depth data of rendered three dimensional objects;
• a plane memory for storing data representing windows used in rendering the displayed image data stored in the frame buffer;
• means for storing object boundary data corresponding to each object which encompasses and is larger than each corresponding object;
• means for defining a pick window with a pick window boundary;
• a front end processor means for identifying each object which has object boundary data that intersects the pick window;
• and
• a rasterization processor means for rerendering each identified object to identify which rerendered objects have object depth data that matches the displayed image depth data.

A process for picking a visible object from multiple three dimensional objects rendered on a graphics video display, comprising the steps of:

• defining a pick window boundary;
• identifying objects within the pick window by comparing object boundaries to pick window boundaries, each object boundary corresponding to an object wherein each object boundary encompasses and is larger than each corresponding object;
• selectively rerendering said identified objects;
• and
• detecting visible objects by matching the depth of the rerendered objects with the depth data for corresponding pixel positions within the pick window boundary.