System and method for accelerated occlusion culling

• US 5,751,291 A
• Filed: 07/26/1996
• Issued: 05/12/1998
• Est. Priority Date: 07/26/1996
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Scott, Noel D., Casey, Robert J., Olsen, Daniel M.
• Primary Examiner(s): Nguyen, Phu K.
• Assistant Examiner(s): Vo, Cliff N.
• Application Number:
  US08/690,433
• Time in Patent Office: 655 Days
• Field of Search: 345/419, 345/420, 345/421, 345/422, 345/423, 345/424, 345/433, 345/434
• US Class Current: 345/422
• CPC Class Codes: G06T 15/405 using Z-buffer

Abstract

An occlusion culling circuit for use in a graphics computer receives graphics primitives data including x and y coordinates for each pixel, a z depth value, and r, g, b, and a or index color data. For each group of primitives, the graphics computer scans the primitive and determines a volume which completely bounds the primitive. The z depth values for the pixels comprising the bounding volume are then compared by the occlusion culling circuit to the depths of the pixels in the already rendered primitives to determine whether any pixels in the incoming primitive are visible. If no pixels are visible, the occlusion culling circuit clears the result register and receives the next graphics primitive. If, on the other hand, one or more pixels is visible, the occlusion culling circuit completely renders the primitives bounded by the bounding volume. Since the graphics primitives which are totally occluded can bypass the more intensive pixel by pixel processing and storage, the speed and efficiency of the graphics computer can be significantly increased.

Claims

1. An occlusion culling circuit for use in a graphics computer, comprising:

a central processor;

a depth comparison circuit for receiving a graphics primitive from said central processor and for comparing an incoming depth value for each address in said graphics primitive with a current depth value for a rendered pixel at a corresponding address, said depth comparison circuit generating a result signal having a first logical value when said incoming depth value passes a depth comparison function and a second logical value when said incoming depth value fails said depth comparison function;

a logic circuit for receiving said result signal of said depth comparison circuit and for generating a depth compare signal, said logic circuit latching said depth compare signal at said first logical value upon receipt of said result signal having said first logical value;

a depth buffer for storing depth values of said graphics primitive;

a color buffer for storing color values of said graphics primitive; and

wherein said central processor stores said color values in said color buffer and said depth values in said depth buffer when said logic circuit latches said first logical value for said graphics primitive.

2. The occlusion culling circuit of claim 1, wherein said logic circuit comprises a logical OR function having an output to a depth compare result register, and having inputs from said depth comparison circuit and said depth compare result register.

3. The occlusion culling circuit of claim 1, further comprising a color mask circuit for storing said color values, and for sending said color values to said color buffer when said first logical value is latched by said logic circuit.

4. The occlusion culling circuit of claim 1, wherein each said address of said graphics primitive corresponds to a pixel in said graphics primitive, and wherein said depth comparison function includes a determination of whether said pixel of said graphics primitive is in front of said rendered pixel.

5. The occlusion culling circuit of claim 1, wherein each said address of said graphics primitive corresponds to a pixel in said graphics primitive, and wherein said depth comparison function includes a determination of whether said pixel of said graphics primitive is behind of said rendered pixel.

6. The occlusion culling circuit of claim 1, wherein each said address of said graphics primitive corresponds to a pixel in said graphics primitive, and wherein said depth comparison function includes a determination of whether said pixel of said graphics primitive is equal to said rendered pixel.

7. The occlusion culling circuit of claim 1, further comprising switch means for enabling and disabling storage of said incoming depth value in said depth buffer based on whether said first logical value is latched by said logic circuit.

8. The occlusion culling circuit of claim 1, wherein said depth comparison circuit receives said current depth value from said depth buffer.

9. The occlusion culling circuit of claim 1, wherein said central processor determines a bounding volume for said graphics primitives.

10. The occlusion culling circuit of claim 3, wherein said color mask circuit can selectively disable components of color data supplied to said color data buffer.

11. A method for accelerated occlusion culling in a graphics computer, comprising the steps of:

receiving data associated with each pixel in a graphics primitive;

performing a depth comparison function by comparing an depth value of one said pixel in said graphics primitive with a current depth value for a rendered pixel at a corresponding address;

generating a result signal having a having a first logical value when said depth value passes said depth comparison function and a second logical value when said depth value fails said depth comparison function;

latching said result signal in a depth compare result register so that said first value remains in said depth compare result register after a first occurrence of said result signal having a first logic value;

reading said depth compare result register to determine if said first logic value was latched in said depth compare result register; and

storing color data values of said graphics primitive in a color buffer and depth data values of said graphics primitive in a depth buffer when said first logic value is read from said depth compare result register.

12. The method of claim 11, further comprising the step of determining a bounding volume for said graphics primitive.

13. The method of claim 11, further comprising the step of clearing said depth compare result register so that said depth compare result register stores said second logical value.

14. The method of claim 11, wherein said depth comparison function is a determination of whether said pixel of said graphics primitive is in front of said rendered pixel.

15. The method of claim 11, wherein said depth comparison function is a determination of whether said pixel of said graphics primitive is behind of said rendered pixel.

16. The method of claim 11, wherein said depth comparison function is a determination of whether said pixel of said graphics primitive is equal to said rendered pixel.

17. The method of claim 11, wherein the step of latching said result signal is performed by a logical OR function having a feedback loop that includes said depth compare result register.

18. An occlusion culling circuit for use in a graphics computer, comprising:

depth comparison means for receiving a bounded volume for a graphics primitive and for comparing a depth value for each pixel in said graphics primitive with a current depth value for a rendered pixel at a corresponding address, said depth comparison circuit generating a result signal having a first logical value when said incoming depth value passes a depth comparison function and a second logical value when said incoming depth value fails said depth comparison function;

latching means for receiving said result signal of said depth comparison means and for generating a depth compare signal, said logic circuit latching said depth compare signal at said first logical value upon receipt of said result signal having said first logical value;

depth buffer means for storing depth values of said graphics primitive;

color buffer means for storing color values of said graphics primitive; and

wherein said central processor stores said color values in said color buffer and said depth values in said depth buffer when said logic circuit latches said first logical value for said graphics primitive.