Rapid computation of local eye vectors in a fixed point lighting unit

• US 6,141,013 A
• Filed: 11/12/1999
• Issued: 10/31/2000
• Est. Priority Date: 02/03/1998
• Status: Expired due to Term

• Current Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Deering, Michael F., Nelson, Scott R.
• Primary Examiner(s): Nguyen, Phu K.
• Application Number:
  US09/439,034
• Time in Patent Office: 354 Days
• Field of Search: 345/426, 345/427, 345/424, 345/419, 345/112, 345/118
• US Class Current: 345/426
• CPC Class Codes: G06T 15/005 General purpose rendering architectures
• CPC Class Codes: G06T 15/50 Lighting effects
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

A rapid method for calculating a local eye vector in a fixed point lighting unit. For a given triangle primitive which is to be projected into a given viewport in screen space coordinates, the local eye vector corresponds to a given eye position and a first vertex of the given triangle primitive. (A different local eye vector is calculated for each vertex of the given triangle primitive). The method first comprises generating a view vector matrix which corresponds to the given eye position and corner coordinates of the given viewport, where the corner coordinates are expressed in screen space coordinates. The view vector matrix is usable to map screen space coordinates to an eye vector space which corresponds to the given viewport. The method next includes receiving a first set of coordinates (in screen space) which correspond to the first vertex. The first set of coordinates are then scaled to a numeric range which is representable by the fixed point lighting unit. Next, the first set of coordinates are transformed using the view vector matrix, which produces a non-normalized local eye vector within the eye vector space for the given viewport. The non-normalized local eye vector is normalized to form a normalized local eye vector. The normalized local eye vector is then usable to perform subsequent lighting computations such as computation of specular reflection values for infinite light sources, producing more realistic lighting effects than if an infinite eye vector were used. These more realistic lighting effects do not come at decreased performance, however, as the local eye vector may be calculated rapidly using this method.

Claims

1. A method for calculating a local eye vector in a graphics sub-system, wherein said local eye vector corresponds to a given eye position and a first vertex of a first geometric primitive, said method comprising:

receiving a first set of coordinates corresponding to said first vertex, wherein said first set of coordinates are represented in a first coordinate space;

generating a reverse transform matrix corresponding to said given eye position, wherein said given eye position is represented by a second set of coordinates located in a second coordinate space;

transforming said first set of coordinates using said reverse transform matrix, wherein said transforming generates a preliminary local eye vector;

wherein said preliminary local eye vector is usable to perform lighting computations upon said first vertex.

2. The method of claim 1, wherein said first coordinate space is screen space, and wherein said second coordinate space is world space.

3. The method of claim 1, further comprising scaling first set of coordinates to a given numeric range, wherein said scaling is performed prior to said transforming.

4. The method of claim 1, further comprising normalizing said preliminary local eye vector, thereby producing a normalized local eye vector, wherein said normalized local eye vector is usable for performing said lighting computations upon said first vertex.

5. The method of claim 4, further comprising:

performing said lighting computations on said first vertex using said normalized local eye vector.

6. The method of claim 5, wherein said performing said lighting computations includes calculating specular highlight values for an infinite light source.

7. The method of claim 1, wherein said reverse transform matrix corresponds to a given viewport within said first coordinate space.

8. The method of claim 7, further comprising:

calculating said reverse transform matrix from coordinates of said given viewport, an inverse of a current viewing matrix, and said given eye position, wherein said current viewing matrix is usable to transform coordinates from said second coordinate space to said first coordinate space.

9. The method of claim 8, wherein said second coordinate space is world space, and wherein said first coordinate space is screen space.

10. The method of claim 1, wherein said transforming is performed using fixed point arithmetic having a predetermined numeric range.

11. The method of claim 10, further comprising:

determining whether said reverse transform matrix is valid for said predetermined numeric range;

performing computation of said local eye vector using floating point arithmetic in response to said determining that said reverse transform matrix is invalid for said predetermined numeric range.

12. A graphics sub-system for calculating a local eye vector, wherein said local eye vector corresponds to a given eye position and a given position value, said graphics sub-system comprising:

a coordinate conversion unit coupled to receive a first set of coordinates corresponding to said given position value, wherein said coordinate conversion unit is configured to generate a second set of coordinates from said first set of coordinates, wherein said first set of coordinates are located in a first coordinate space, and wherein said second set of coordinates are located in a second coordinate space;

a lighting unit coupled to receive said second set of coordinates and a reverse transform matrix corresponding to said given eye position, wherein said lighting unit is configured to generate a preliminary local eye vector by transforming said second set of coordinates using said reverse transform matrix, wherein said lighting unit is configured to utilize said preliminary local eye vector in performing lighting computations on said given position value.

13. The graphics sub-system of claim 12, wherein said first coordinate space is world space, and wherein said second coordinate space is screen space.

14. The graphics sub-system of claim 12, wherein said coordinate conversion unit is configured to utilize floating point arithmetic to generate said second set of coordinates, and wherein said lighting unit is configured to utilize fixed point arithmetic to generate said preliminary local eye vector.

15. The graphics sub-system of claim 14, wherein said lighting unit is configured to scale said second set of coordinates to a predetermined fixed point numeric range before generation of said preliminary local eye vector.

16. The graphics sub-system of claim 12, wherein said preliminary local eye vector is non-normalized, wherein said lighting unit is configured to normalize said preliminary local eye vector, wherein said normalized local eye vector is usable to perform said lighting computations on said given position value.

17. The graphics sub-system of claim 12, wherein said reverse transform matrix corresponds to a given viewport within screen space.

18. The graphics sub-system of claim 17, wherein said reverse transform matrix is calculated using said given eye position, coordinates of said given viewport, and an inverse of a current viewing matrix, wherein said current viewing matrix is usable by said coordinate conversion unit for transforming coordinates from said first coordinate space to said second coordinate space.

19. The graphics sub-system of claim 12, wherein said lighting unit is configured to calculate specular highlight values for said given position value, wherein said specular highlight values are modeled as originating from an infinite light source.

20. The graphics sub-system of claim 12, further comprising:

a setup unit coupled to said coordinate conversion unit, wherein said setup unit is configured to receive said second set of coordinates concurrently with said lighting unit, wherein said setup unit is configured to perform setup operations on a geometric primitive including said given position value.

21. A computer system for calculating a local eye vector, wherein said local eye vector corresponds to a given eye position and a given position value, said computer system comprising:

a host CPU configured to generate a reverse transform matrix corresponding to said given eye position, wherein said given eye position is represented by coordinates located in a first coordinate space;

a graphics sub-system coupled to said host CPU, said graphics sub-system comprising;

a coordinate conversion unit coupled to receive a first set of coordinates corresponding to said given position value, wherein said coordinate conversion unit is configured to generate a second set of coordinates from said first set of coordinates, wherein said first set of coordinates are located in said first coordinate space, and wherein said second set of coordinates are located in a second coordinate space;

a lighting unit coupled to receive said second set of coordinates and said reverse transform matrix, wherein said lighting unit is configured to generate a preliminary local eye vector by transforming said second set of coordinates using said reverse transform matrix, wherein said lighting unit is configured to utilize said preliminary local eye vector in performing lighting computations on said given position value.

22. The computer system of claim 21, wherein said first coordinate space is world space, and wherein said second coordinate space is screen space.

23. The computer system of claim 22, wherein said coordinate conversion unit is configured to utilize floating point arithmetic to generate said second set of coordinates, and wherein said lighting unit is configured to utilize fixed point arithmetic to generate said preliminary local eye vector.

24. The computer system of claim 22, wherein said reverse transform matrix corresponds to a given viewport within screen space.

25. The computer system of claim 24, wherein said reverse transform is calculated using said given eye position, coordinates of said given viewport, and an inverse of a current viewing matrix, wherein said current viewing matrix is usable by said coordinate conversion unit for transforming coordinates from said first coordinate space to said second coordinate space.

26. A system for calculating a local eye vector, wherein said local eye vector corresponds to a given eye position and a first vertex of a first geometric primitive, said system comprising:

receiving means for receiving a first set of coordinates corresponding to said first vertex, wherein said first set of coordinates are represented in a first coordinate space;

generating means for generating a reverse transform matrix corresponding to said given eye position, wherein said given eye position is represented by a second set of coordinates located in a second coordinate space;

transforming means for transforming said first set of coordinates using said reverse transform matrix, wherein said transforming generates a preliminary local eye vector;

wherein said preliminary local eye vector is usable to perform lighting computations upon said first vertex.