Three dimensional graphics systems

Abstract

An apparatus and a method for generating 3-dimensional computer graphic images. The image is first sub-divided into a plurality of rectangular areas ( 2 ). A display list memory ( 4 ) is loaded with object data for each rectangular area. The image and shading data for each picture element of each rectangular area are derived from the object data in the image synthesis processor ( 6 ) and a texturing and shading processor ( 10 ). A depth range generator ( 12 ) derives a depth range for each rectangular area from the object data as the imaging and shading data is derived. This is compared with the depth of each new object to be provided to the image synthesis processor ( 6 ) and the object may be prevented from being provided to the image synthesis processor ( 6 ) independence on the result of the comparison.

1 . A method for generating 3-dimensional computer graphic images comprising the steps of: 
 sub-dividing the image into a plurality of rectangular areas;    loading object data for each rectangular area into a display list memory;    deriving image data and shading data for each picture element of each rectangular area from the object data;    providing the shading data for display;    characterised by: 
 deriving a range of depth values for each rectangular area from the object data;  
 comparing the depth of each new object to be provided to the image data deriving step for a rectangular area with the depth range for that rectangular area, and preventing the new object data from being provided to the image data deriving step in dependence on the result of the comparison.  
   
     
     
         2 . A method according to  claim 1  in which the preventing step prevents object data being read from the display list memory.  
     
     
         3 . A method according to  claim 1  in which the preventing step prevents object data being loaded into the display list memory.  
     
     
         4 . A method according to  claim 1  in which the step of deriving a range of depth values comprises deriving the minimum and maximum depths for the objects in the rectangular area.  
     
     
         5 . A method according to  claim 4  in which the step of deriving the minimum and maximum depths for objects in the rectangular area is performed on a plurality of subsets of pixels in the rectangular area, and including the step of combining the results for this plurality of subsets of pixels to produce the range for the rectangular area.  
     
     
         6 . A method according to  claim 5  in which the combining step is performed with a tree structure of comparators.  
     
     
         7 . A method according to  claim 6  in which the comparators at higher levels in the tree structure have greater precision than the comparators at lower levels.  
     
     
         8 . Apparatus for generating 3-dimensional computer graphic images comprising; 
 means for sub-dividing the image into a plurality of rectangular areas;    a display list memory into which object data for each rectangular area is loaded;    means for deriving image and shading data for each picture element of each rectangular area from the object data;    means for providing the shading data for display;    characterised by: 
 means for deriving a depth range for each rectangular area from the object data as the image and shading data is derived means for comparing the depth of each new object to be provided to the image data deriving means with the current range from that rectangular area; and  
 means for preventing the new object data from being provided to the image data deriving means in dependence on the result of the comparison.  
   
     
     
         9 . A method according to  claim 8  in which the preventing means prevents object data from being read from the display list memory.  
     
     
         10 . A method according to  claim 8  in which the preventing means prevents object data from being loaded into the display list memory.  
     
     
         11 . Apparatus according to  claim 8  in which the means for deriving a depth range comprises means for deriving the minimum and maximum depths for the objects in the rectangular areas.  
     
     
         12 . Apparatus according to  claim 11  in which the means for deriving the minimum and maximum depths for the objects in the rectangular areas operates on a plurality of subsets of pixels and includes means to combine the results for the subsets to produce the range for the rectangular areas.  
     
     
         13 . Apparatus according to  claim 12  in which the combining means comprises a tree structure of comparators.  
     
     
         14 . Apparatus according to  claim 13  in which the comparators at higher levels in the tree structure have greater precision than the comparators at lower levels.  
     
     
         15 . Apparatus for generating 3-dimensional computer graphic images substantially as herein described with reference to FIGS. 4 and 6 of the drawings.  
     
     
         16 . A method for generating 3-dimensional computer graphic images substantially as herein described.