Planar z representation for z compression

• US 7,382,368 B1
• Filed: 06/28/2004
• Issued: 06/03/2008
• Est. Priority Date: 06/28/2004
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: Molnar, Steven E., French, Mark J., Montrym, John S., Schneider, Bengt-Olaf, Wilde, Daniel P.
• Primary Examiner(s): Tung; Kee M.
• Assistant Examiner(s): Hsu; Joni
• Application Number:
  US10/878,460
• Time in Patent Office: 1,436 Days
• Field of Search: 345/421, 345/418, 345/422, 345/613, 345/614, 345/612, 345/581, 345/555, 345/530
• US Class Current: 345/421
• CPC Class Codes: G06T 15/405 using Z-buffer
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

A z buffer stores compressed z data represented in a planar format for one or more tiles. The compressed format includes a set of tile specific coefficients defining a plane equation for each z tested primitive intersecting the tile. The z buffer stores a maximum number of sets of tile specific coefficients for each tile, and when the maximum number of sets is exceeded for a particular tile, an uncompressed format is used to store the z data for the particular tile.

Claims

1. A z operations unit, comprising:

a source z evaluation unit configured to compute a source z value using tile specific coefficients for a plane equation defining a fragment of a source primitive, wherein the fragment is a portion of the source primitive that is within a tile, wherein the tile includes portions of at least two scanlines each of the tile specific coefficients based on a reference position within the tile wherein the reference position is unique to the tile and is not shared with any other tiles that are intersected by the primitive;

a z triage unit configured to determine a minimum source z value and a maximum source z value for the fragment using the tile specific coefficients and produce a trivial z test result that indicates whether the fragment should be rejected, the fragment should be accepted, or that the source z value should be computed and compared with a destination z value;

a destination z evaluation unit configured to receive destination z data from a z buffer and produce the destination z value; and

a z test unit configured to determine whether or not the source z value or the destination z value should be stored in the z buffer.

2. The z operations unit of claim 1, further comprising:

a stencil test unit configured to determine whether or not the source z value passes a stencil test.

3. The z operations unit of claim 1, further comprising:

a destination z write unit configured to write the source z value represented in a compressed or uncompressed format to the z buffer when the z test unit determines the source z value should be stored in the z buffer.

4. The z operations unit of claim 1, wherein the z triage unit is further configured to determine a minimum destination z value and a maximum destination z value using the destination z data and output the trivial z test result to the z test unit.

5. The z operations unit of claim 1, wherein the source z value and the destination z value each correspond to a sub-pixel sample position specified by a multisample mode.

6. The z operations unit of claim 5, wherein the source z evaluation unit is further configured to compute a z value for each sub-pixel sample position using the destination z data to produce destination z values.

7. The z operations unit of claim 6, wherein each sub-pixel sample position is specified by a multisample mode.

8. The z operations unit of claim 1, wherein the z operations unit is included within a raster operations unit configured to receive fragment data and produce z data.

9. The z operations unit of claim 1, wherein the tile specific coefficients are produced by a rasterizer.

10. The z operations unit of claim 1, further comprising a means for writing the set of tile specific coefficients to a z buffer.

11. The z operations unit of claim 1, including a z buffer for storing the tile specific coefficients for the plane equation defining the fragment in when the trivial z test result indicates the fragment should be accepted.

12. The z operations unit of claim 1, wherein the z triage unit is configured to reject the tile specific coefficients for the plane equation defining the fragment in a z buffer when the trivial z test result indicates the fragment should be rejected.