Three-dimensional computer graphics system

Abstract

A method and apparatus provided for rendering three-dimensional computer graphic images which include both translucent and opaque objects. A list of objects which may be visible in the image is determined and for each pixel in the image a determination is made as to whether or not an object for the list may be visible at that pixel. A data tag is stored for a transparent object determined to be visible at a pixel and the tag and object data are passed to a texturing and shading unit when a translucent object is determined to be overwriting the location in the tag buffer already occupied by another data tag.

1 . A method for rendering 3-dimensional computer graphic images which include translucent and opaque objects comprising the steps of: 
 determining a list of objects which may be visible in the image;    for each pixel in the image determining whether or not an object from the list may be visible at that pixel;    storing a data tag for transparent object determined to be visible pixel in a tag buffer; and    passing tag data and object data to a texturing and shading unit (TSU) when a translucent object is determined to be overwriting a location in the tag buffer already occupied by another data tag.    
     
     
         2 . A method according to  claim 1  including the steps of: 
 storing at least one additional tag each time a translucent object is determined to be visible at a pixel the additional tag being stored in a separate location to any previously stored tag; and    in which the step of passing tag and object data to the TSU is performed from the first stored tag when all tag storage locations are full.    
     
     
         3 . A method according to  claim 2  including the step of: 
 clearing all tags when an opaque surface is determined to be visible at a pixel; and    storing a tag associated with the opaque surface.    
     
     
         4 . A method according to  claim 1  including the step of initially subdividing a scene to be rendered into a plurality of rectangular sub-regions and subsequently performing the method for each sub-region.  
     
     
         5 . A method according to  claim 1  including the step of determining whether or not an object is a punch through object and performing a different process when a punch through object is detected.  
     
     
         6 . A method according to  claim 5  including the step of determining whether the punch through object is an opaque object, and if an opaque object is detected, clearing all tags from the tag buffer for pixels intersected by that object and sending the punch through object data to the TSU.  
     
     
         7 . A method according to  claim 5  including the step of determining whether the punch through object is translucent and if a translucent object is detected passing all data tags and object data for a pixel to the TSU, including the object data for the translucent punch through object.  
     
     
         8 . An apparatus for rendering 3-dimensional computer graphic images which include translucent and opaque objects comprising: 
 means for determining a list of objects which may be visible in the image;    means for determining for each pixel in the image whether or not an object from the list may be visible at that pixel;    a tag buffer for storing a data tag for a translucent object determined to be visible at a pixel; and    means for passing tag data and object data to a texturing and shading unit (TSU) when a translucent object is determined to be overwriting a location in the tag buffer already occupied by another data tag.    
     
     
         9 . An apparatus according to  claim 8  including means for storing at least one additional tag each time a translucent object is determined to be visible at a pixel, the pixel tag being stored in a separate location in the tag buffer to any previously stored tag; and 
 in which the means for passing tag and object data to the TSU performs this step from the first stored tag when all tag storage locations are full.    
     
     
         10 . An apparatus according to  claim 9  including means for clearing all tags when an opaque surface is determined to be visible at a pixel; and 
 means for storing in the tag buffer a tag associated with the opaque surface.    
     
     
         11 . An apparatus according to  claim 8  including means for initially sub-dividing a scene to be rendered into a plurality of rectangular sub-regions and subsequently operating on each sub-region.  
     
     
         12 . An apparatus according to  claim 8  including means for determining whether or not an object is a punch through object and means for performing a different process when a punch through object is detected.  
     
     
         13 . An apparatus according to  claim 12  including means for determining whether or not a punch through object is an opaque object and means for clearing all tags from the tag buffer for pixels intercepted by an opaque punch through object and means for sending the opaque punch through object data to the TSU.  
     
     
         14 . An apparatus according to  claim 12  including the steps of determining whether or not the punch through object is a translucent and if a translucent punch through object is detected passing all data tags and object data for a pixel to the TSU, including the object data for the translucent punch through object.