Method and apparatus for implementing level of detail with ray tracing
View Patent ↗The present invention relates to computer graphics applications involving scene rendering using objects modeled at multiple levels of detail. In accordance with an aspect of the invention, a ray tracer implementation allows users to specify multiple versions of a particular object, categorized by LOD ID's. A scene server selects the version appropriate for the particular scene, based on the size of the object on the screen for example, and provides a smooth transition between multiple versions of an object model. In one example, the scene server will select two LOD representations associated with a given object and assign relative weights to each representation. The LOD weights are specified to indicate how to blend these representations together. A ray tracer computes the objects hit by camera rays associated with pixels in the camera window, as well as secondary rays in recursive implementations, and rays striking LOD objects are detected and shaded in accordance with the weights assigned to the different representations. Embodiments are disclosed for level of detail control using both forward ray tracing and backward ray tracing, including handling of camera rays, reflected rays, refracted rays and shadow rays.
1. A graphics apparatus for rendering a scene including an object having more than one representation, the apparatus comprising:
a rendering system that computes a first point of intersection between a first level of detail (LOD) of the object and a ray corresponding to a view of the scene, and a second point of intersection between a second LOD of the object and the ray.
2. A graphics apparatus according to claim 1 , wherein the rendering system further determines first and second colors respectively associated with the first and second points of intersection.
3. A graphics apparatus according to claim 2 , wherein the rendering system further blends the first and second colors to provide a combined color for a pixel corresponding to the ray.
4. A graphics apparatus according to claim 3 , wherein the rendering system blends the first and second colors in accordance with first and second weights respectively associated with the first LOD and the second LOD.
5. A graphics apparatus according to claim 1 , wherein the rendering system selects the first LOD and the second LOD from among a plurality of LODs.
6. A graphics apparatus according to claim 5 , wherein the rendering system selects the representations in accordance with a perceived size of the object in the scene.
7. A graphics apparatus, comprising:
a scene server for identifying an appropriate representation of an object among more than one representation of the object, each representation having a corresponding level of detail; and
a ray tracer coupled to the scene server that computes a first point of intersection between a first LOD of the object and a ray corresponding to a view of a scene including the object, and a second point of intersection between a second LOD of the object and the ray.
8. A graphics apparatus according to claim 7 , further comprising a shader that determines a respective color associated with the first and second points of intersection.
9. A graphics apparatus according to claim 7 , wherein weights are respectively associated with the appropriate and alternate representations.
10. A graphics apparatus according to claim 9 , wherein weights are respectively associated with the appropriate and alternate representations, the shader further determining a final color based on the respective colors and the respective weights.
11. A graphics apparatus according to claim 7 , wherein the ray tracer generates a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
12. A graphics apparatus according to claim 8 , wherein the ray tracer generates a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
13. A graphics apparatus according to claim 7 , wherein the ray is a camera ray.
14. A graphics apparatus according to claim 8 , wherein the ray is a camera ray.
15. A graphics apparatus according to claim 7 , wherein the ray is a shadow ray.
16. A graphics apparatus according to claim 8 , wherein the ray is a shadow ray.
17. A graphics apparatus according to claim 7 , wherein the ray is one of a refracted ray and a reflected ray.
18. A graphics apparatus according to claim 8 , wherein the ray is one of a refracted ray and a reflected ray.
19. A graphics apparatus, comprising:
means for identifying an appropriate representation of an object among more than one representation of the object, each representation having a corresponding level of detail; and
means for computing a first point of intersection between a first LOD of the object and a ray corresponding to a view of a scene including the object, and a second point of intersection between a second LOD of the object and the ray.
20. A graphics apparatus according to claim 19 , further comprising means for determining a respective color associated with the first and second points of intersection.
21. A graphics apparatus according to claim 19 , further comprising means for respectively associating weights with the appropriate and alternate representations.
22. A graphics apparatus according to claim 20 , further comprising means for respectively associating weights with the appropriate and alternate representations, the determining means including means for further determining a final color based on the respective colors and the respective weights.
23. A graphics apparatus according to claim 19 , further comprising means for generating a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
24. A graphics apparatus according to claim 20 , further comprising means for generating a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
25. A graphics apparatus according to claim 19 , wherein the ray is a camera ray.
26. A graphics apparatus according to claim 20 , wherein the ray is a camera ray.
27. A graphics apparatus according to claim 19 , wherein the ray is a shadow ray.
28. A graphics apparatus according to claim 20 , wherein the ray is a shadow ray.
29. A graphics apparatus according to claim 19 , wherein the ray is one of a refracted ray and a reflected ray.
30. A graphics apparatus according to claim 20 , wherein the ray is one of a refracted ray and a reflected ray.
31. A graphics method, comprising:
identifying an appropriate representation of an object among more than one representation of the object, each representation having a corresponding level of detail (LOD); and
computing a first point of intersection between a first LOD of the object and a ray corresponding to a view of a scene including the object, and a second point of intersection between a second LOD of the object and the ray.
32. A graphics method according to claim 31 , further comprising determining a respective color associated with the first and second points of intersection.
33. A graphics method according to claim 31 , further comprising respectively associating weights with the appropriate and alternate representations.
34. A graphics method according to claim 32 , further comprising respectively associating weights with the appropriate and alternate representations, the determining step including determining a final color based on the respective colors and the respective weights.
35. A graphics method according to claim 31 , further comprising generating a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
36. A graphics method according to claim 32 , further comprising generating a ray tree based on the first point of intersection and a sibling ray tree based on the second point of intersection.
37. A graphics method according to claim 31 , wherein the ray is a camera ray.
38. A graphics method according to claim 32 , wherein the ray is a camera ray.
39. A graphics method according to claim 31 , wherein the ray is a shadow ray.
40. A graphics method according to claim 32 , wherein the ray is a shadow ray.
41. A graphics method according to claim 31 , wherein the ray is one of a refracted ray and a reflected ray.
42. A graphics method according to claim 32 , wherein the ray is one of a refracted ray and a reflected ray.
43. A graphics method according to claim 31 , wherein the identifying step includes: determining a perceived size of the object;
comparing the perceived size with a value corresponding to the perceived size respectively associated with each representation; and
identifying the appropriate and alternate representations in accordance with a result of the comparing step.
44. A graphics method according to claim 43 , further comprising respectively associating weights with the appropriate and alternate representations in accordance with the result of the comparing step.
45. A graphics method according to claim 44 , further comprising determining a respective color associated with the first and second points of intersection and the respective weights.