Parameter compaction in tile based rendering device

1. A method for managing memory usage in a three-dimensional computer graphics system, the method comprising the steps of:

dividing a scene to be textured and shaded into a plurality of rectangular areas, each area comprising a plurality of picture elements in the scene;

deriving a list of objects for each rectangular area, each list comprising objects which may be visible in the scene;

removing from each list all objects that do not contribute to the final textured and shaded scene;

determining depth and stencil data for each object in the scene;

compiling a buffer of tags for the frontmost visible object for each pixel within the scene;

reducing the list of objects to be rendered by using the depth and stencil data for hidden surface removal in combination with the buffer of tags; and

texturing and shading each rectangular area using the reduced lists of objects for each rectangular area, wherein the removing step comprises the step of processing the buffer of the tags to regenerate the object list for each tile for only those objects required to correctly render the scene, the object list being subsequently rendered in the texturing and shading step.

2. The method according to claim 1 , wherein the removing step comprises the step of regenerating the list using the data stored in the tag buffer.

3. The method according to claim 1 , wherein a determination is made whenever an object does not update the tag buffer as to whether or not the scene should be textured and shaded.

4. The method according to claim 1 , wherein the method operates on one rectangular area at a time.

5. The method according to claim 1 , wherein the method operates on the plurality of rectangular areas forming a macro area, each macro area being smaller than the area of the whole scene.

6. The method according to claim 1 , wherein the regenerating step includes the steps of generating a pointer to insert into a new object list for the rectangular area, and setting a flag for each memory location that is referenced by a tag.

7. The method according to claim 1 further including the step of compacting memory allocated to rectangular areas to free unused memory.

8. An apparatus for managing memory usage in a three-dimensional computer graphics system comprising:

means for dividing a scene to be textured and shaded into a plurality of rectangular areas, each area comprising a plurality of picture elements in the scene;

means for deriving a list of objects for each rectangular area, each list comprising objects which may be visible in the scene;

means for removing from each list all objects that do not contribute to the final textured and shaded;

means for determining depth and stencil data for each object in the scene;

means for compiling a buffer of tags for the frontmost visible object for each pixel within the scene;

means for reducing the list of objects to be rendered by using the depth and stencil data for hidden surface removal in combination with the buffer of tags; and

means for texturing and shading each rectangular area using the reduced lists of objects for each rectangular area, wherein the removing means comprises means for processing the buffer of the tags to regenerate the object list for each tile for only those objects required to correctly render the scene, the object list being subsequently rendered in the texturing and shading means.

9. An apparatus according to claim 8 , wherein the regenerating means includes means for generating a pointer to insert into a new object list for the rectangular area, and means for setting a flag for each memory location that is referenced by a tag.