Method and apparatus for modeling specular reflection

• US 6,545,677 B2
• Filed: 04/30/2001
• Issued: 04/08/2003
• Est. Priority Date: 05/21/1999
• Status: Expired due to Term

• Current Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Brown, Russell A.
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Sealey, Lance W.
• Application Number:
  US09/845,781
• Publication Number:
  US 20010048434A1
• Time in Patent Office: 708 Days
• Field of Search: 345/426, 345/420, 345/474, 345/473, 345/582
• US Class Current: 345/426
• CPC Class Codes: G06T 15/506 Illumination models

Abstract

A method and apparatus for modeling the specular reflection of light from an object is disclosed. In accordance with one embodiment of the method, a portion of the object is modeled by one or more surfaces each having at least one vertex and an edge point corresponding to an edge. A sine value associated with a highlight angle is determined at each vertex and edge point, and a control value is determined at each vertex and edge point using the sine values. A specular input component at each point on the surface is determined using the control values. The specular input component is utilized to determine the specular light component at that particular point. Embodiments of apparatus implementing the method are also disclosed.

Claims

1. A system comprising

a processor;

a memory coupled to said processor;

code executed by said processor configured to determine a specular reflection component of an object to be graphically imaged, comprising the steps of;

modeling a portion of said object to be imaged with one or more surfaces having at least one vertex and at least one edge having an edge point corresponding thereto;

determining a sine value associated with a highlight angle at each vertex and edge point;

determining a control value at each vertex and edge point based upon said sine values;

determining a specular input value at a particular point on said surface from said control values; and

determining a specular reflection component at said point based on said specular input value at said point.

2. The system in accordance with claim 1, wherein said surface comprises a quadratic triangular Bezier surface.

3. The system in accordance with claim 2, wherein each edge point comprises a midpoint corresponding to each edge of said surface.

4. The system in accordance with claim 1, wherein said step of calculating said sine value comprises calculating the sine square value of said angle.

5. The system in accordance with claim 1, wherein said highlight angle comprises the angle between a halfway vector and a normal vector at each vertex and edge point.

6. The system in accordance with claim 1, wherein said highlight angle comprises the angle between a view vector and a reflection vector at each vertex and edge point.

7. The system in accordance with claim 1 wherein said step of determining a specular input value at a particular point comprises determining such a value dependent upon said control values and a positional relationship of said particular point with respect to said vertices and edge points.

8. The system in accordance with claim 1, further including the step of reparametrizing said specular input value at said point on a scale between 1 and 0 and wherein said specular reflection component is determined from said reparametrized specular input value.

9. The system in accordance with claim 8, wherein said step of reparametrizing comprises obtaining a value r by subtracting a predetermined low specular input value from said specular input value at said point and dividing said result by the difference between a predetermined high specular input value and said low specular input value, producing a value t, and where r=1−

t²(3−

2t).

10. The system in accordance with claim 1 further including the step of reparametrizing said specular input value at said point using a cubic spline function.

11. The system in accordance with claim 1, wherein said surface has vertices P₀, P₁, and P₂ and edge points P₃, P₄, and P₅, said control values S₀, S₁, S₂, S₃, S₄ and S₅ at P₀, P₁, P₂, P₃, P₄ and P₅, respectively, comprise s₀, s₁, s₂, (4s₃−

s₀−

s₁)/2, (4s₄−

s₁−

s₂)/2 and (4s₅−

s₂−

s₀)/2, where s₀, s₁, s₂, s₃, s₄ and s₅ represent said sine values at P₀, P₁, P₂, P₃, P₄ and P₅.

12. The system in accordance with claim 11, wherein said specular input value at said point comprises (b₀S₀+2b₁S₃)b₀+(b₁S₁+2b₂S₄)b₁+(b₂S₂+2b₀S₅)b₂, where b₀, b₁ and b₂ are barycentric coordinates of said point relative to said vertices P₀, P₁ and P₂.

13. The system in accordance with claim 1, wherein said sine value at each vertex and edge midpoint comprises the square of the dot product between a normal vector and a halfway vector, subtracted from the value 1.

14. The system in accordance with claim 1, wherein said specular input value is obtained from a set of barycentric coordinates for said point in relation to said vertices and edge points and said sine values at said vertices and edge points.

15. The system in accordance with claim 1, further including the step of determining a light data component for said point comprising an ambient light component, a diffuse light component and said specular light component.

16. A method of determining a specular reflection component of an object to be graphically imaged, comprising the steps of:

modeling a portion of said object to be imaged with one or more surfaces having at least one vertex and at least one edge having an edge point corresponding thereto;

determining a specular input value at a particular point on said surface; and

determining a specular reflection component at said point based on said specular input value at said point.

17. The method in accordance with claim 16 wherein a sine value associated with a highlight angle at each vertex and edge point is determined.

18. The method in accordance with claim 17 wherein a control value at each vertex and edge point based upon said sine values is determined.

19. The method in accordance with claim 18 wherein a specular input value at a particular point on said surface is determined from said control values.

20. The method in accordance with claim 19, wherein said surface comprises a quadratic triangular Bezier surface.

21. The method in accordance with claim 20, wherein each edge point comprises a midpoint corresponding to each edge of said surface.

22. The method in accordance with claim 19, wherein said step of calculating said sine value comprises calculating the sine square value of said angle.

23. The method in accordance with claim 19, wherein said highlight angle comprises the angle between a halfway vector and a normal vector at each vertex and edge point.

24. The method in accordance with claim 19, wherein said highlight angle comprises the angle between a view vector and a reflection vector at each vertex and edge point.

25. The method in accordance with claim 19, wherein said step of determining a specular input value at a particular point comprises determining such a value dependent upon said control values and a positional relationship of said particular point with respect to said vertices and edge points.

26. The method in accordance with claim 19, further including the step of reparametrizing said specular input value at said point on a scale between 1 and 0 and wherein said specular reflection component is determined from said reparametrized specular input value.

27. The method in accordance with claim 26, wherein said step of reparametrizing comprises obtaining a value r by subtracting a predetermined low specular input value from said specular input value at said point and dividing said result by the difference between a predetermined high specular input value and said low specular input value, producing a value t, and where r=1−

t²(3−

2t).

28. The method in accordance with claim 19, further including the step of reparametrizing said specular input value at said point using a cubic spline function.

29. The method in accordance with claim 19, wherein said surface has vertices P₀, P₁, and P₂ and edge points P₃, P₄, and P₅, said control values S₀, S₁, S₂, S₃, S₄ and S₅ at P₀, P₁, P₂, P₃, P₄ and P₅, respectively, comprise s₀, s₁, s₂, (4s₃−

s₀−

s₁)/2, (4s₄−

s₁−

s₂)/2 and (4s₅−

s₂−

s₀)/2, where s₀, s₁, s₂, s₃, s₄ and represent said sine values at P₀, P₁, P₂, P₃, P₄ and P₅.

30. The method in accordance with claim 19, wherein said specular input value at said point comprises (b₀S₀+2b₁S₃)b₀+(b₁S₁+2b₂S₄)b₁+(b₂S₂+2b₀S₅)b₂, where b₀, b₁ and are barycentric coordinates of said point relative to said vertices P₀, P₁ and P₂.

31. The method in accordance with claim 30, wherein said sine value at each vertex and edge midpoint comprises the square of the dot product between a normal vector and a halfway vector, subtracted from the value 1.

32. The method in accordance with claim 19, wherein said specular input value is obtained from a set of barycentric coordinates for said point in relation to said vertices and edge points and said sine values at said vertices and edge points.

33. The method in accordance with claim 19, further including the step of determining a light data component for said point comprising an ambient light component, a diffuse light component and said specular light component.