Rendering with point sampling and pre-computed light transport information

• US 9,704,283 B2
• Filed: 03/10/2014
• Issued: 07/11/2017
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Original Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Inventors: Ozdas, Cuneyt, Peterson, Luke Tilman
• Primary Examiner(s): Tryder, Gregory J
• Assistant Examiner(s): Sonners, Scott E
• Application Number:
  US14/203,094
• Publication Number:
  US 20140333623A1
• Time in Patent Office: 1,219 Days
• CPC Class Codes: G06T 15/00 3D [Three Dimensional] image rendering
• CPC Class Codes: G06T 15/06 Ray-tracing
• CPC Class Codes: G06T 15/08 Volume rendering
• CPC Class Codes: G06T 15/50 Lighting effects
• CPC Class Codes: G06T 15/60 Shadow generation
• CPC Class Codes: G06T 15/80 Shading
• CPC Class Codes: G06T 2215/06 Curved planar reformation of 3D line structures
• CPC Class Codes: G06T 2215/12 Shadow map, environment map

Abstract

Rendering system combines point sampling and volume sampling operations to produce rendering outputs. For example, to determine color information for a surface location in a 3-D scene, one or more point sampling operations are conducted in a volume around the surface location, and one or more sampling operations of volumetric light transport data are performed farther from the surface location. A transition zone between point sampling and volume sampling can be provided, in which both point and volume sampling operations are conducted. Data obtained from point and volume sampling operations can be blended in determining color information for the surface location. For example, point samples are obtained by tracing a ray for each point sample, to identify an intersection between another surface and the ray, to be shaded, and volume samples are obtained from a nested 3-D grids of volume elements expressing light transport data at different levels of granularity.

Claims

1. A method for use in rendering a computer graphics image from 3-D scene data, comprising:

tracing, by a processor, a ray in a 3-D scene defined by said 3-D scene data, in a direction and originating from a point up to a first end of a transition zone, and continuing through the transition zone to a second end of the transition zone;

wherein the first end of the transition zone is separated from the point by a first distance, such that the ray is traced the first distance before entering the transition zone, and the second end of the transition zone is separated from the point by a second distance greater than the first distance;

if no intersection was detected for the ray closer than the first end of the transition zone, then

marching a conic section through a 3-D grid of volume elements in the 3-D scene, each volume element associated with data representative of light energy propagating from that volume element, wherein an area of the conic section is determined based on a spreading factor and a distance from the point in the 3-D scene, and

collecting light energy data from volume elements intersected by the conic section during the marching; and

producing, by a processor, shading information for the point in the 3-D scene from the collected light energy from the volume elements, wherein said shading information is used in rendering said computer graphics image.

2. The method for use in rendering a computer graphics image of claim 1, wherein the data representing light energy propagating from each volume element comprises directional and intensity data associated with respective surfaces of elements of a nested structure located in the 3-D scene, the elements of the nested structure having different granularity, where more granular elements represent smaller volumes in the 3-D scene and more precisely represent the directional and color intensity data, and less granular elements comprise a blending of the directional and color intensity data of a plurality of more granular elements.

3. The method for use in rendering a computer graphics image of claim 1, wherein the data representing the light energy propagating through each volume element comprises respective data for light energy propagating through surfaces of each volume element.

4. The method for use in rendering a computer graphics image of claim 1 wherein the marching of the conic section is axially centered along the direction of the ray.

5. The method for use in rendering a computer graphics image of claim 1, further comprising, if an intersection was detected for the ray between the first end and the second end of the transition zone, producing the lighting information by blending lighting information resulting from shading the intersection with collected light energy from surfaces of the volume elements intersected by the conic section within the transition zone.

6. The method for use in rendering a computer graphics image of claim 1, wherein the marching comprises selecting a set of volume elements that form a continuous volume that includes a volume enclosed by the ray.

7. The method for use in rendering a computer graphics image of claim 1, further comprising determining a size of the conic section at a specific distance from the point in the 3-D scene based on a spreading factor and the specific distance from the point.

8. The method for use in rendering a computer graphics image of claim 1, wherein the 3-D grid of volume elements in the 3-D scene comprises a nested set of volume elements, volume elements in the nested set having data representative of a blend of light energy propagating through the surfaces of elements nested therein, if any, and further comprising determining a size of the volume element to be sampled at a given distance from the point in the 3-D scene based on a spreading factor and that distance from the point where the ray originated.

9. The method for use in rendering a computer graphics image of claim 1, wherein the 3-D grid of volume elements is one grid of a plurality of 3-D grids of volume elements in the 3-D scene, wherein different 3-D grids of the plurality have constituent volume elements of different sizes.

10. The method for use in rendering a computer graphics image of claim 9, wherein the marching comprises iteratively determining a location in the 3-D scene to be sampled, selecting the 3-D grid of volume elements from the plurality of 3-D grids of volume elements to be used in that sampling, and performing the sampling.

11. The method for use in rendering a computer graphics image of claim 1, wherein the marching comprises marching the conic section through the transition zone and the producing of the shading information comprises performing a depth-dependent blending of the lighting information in the transition zone with shading information resulting from shading an intersection.

12. The method for use in rendering a computer graphics image of claim 1, wherein the one or more 3-D grid of volume elements in the 3-D scene are separate from an acceleration structure used to trace rays in the 3-D scene.

13. The method for use in rendering a computer graphics image of claim 1, wherein the marching comprises selecting a set of volume elements comprising a plurality of elements, of at least two different sizes, and a spatial arrangement of the set of volume elements relative to an origin of the ray provides progressively larger volume elements with increasing distance from the ray origin.

14. A method for use in rendering a computer graphics image from 3-D scene data comprising one or more geometrical objects, comprising:

providing in a computer graphics processing system a hierarchical acceleration structure comprising elements that each bound a respective portion of a 3-D scene defined by said 3-D scene data, and which collectively bound the one or more objects;

providing in said computer graphics processing system a 3-D grid of volume elements in the 3-D scene, each volume element associated with data representative of light energy propagating from that volume element;

identifying a point on a surface of an object in the 3-D scene for which shading information is to be provided;

defining one or more rays to be emitted from the point, each ray including a respective spreading factor;

determining a respective threshold distance for each of the rays based on the spreading factor for that ray;

wherein the threshold specifies a range, ending with a maximum distance from the point;

tracing, by a processor, each of the one or more rays in the 3-D scene by traversing the hierarchical acceleration structure to identify a respective closest intersection, if any, that is within the maximum distance defined by the threshold distance from the point on the surface, and shading such intersection to produce shading information;

for each ray, if no intersection was identified within the maximum distance, then sampling the 3-D grid of volume elements that are within a conic section of the ray defined by a direction of the ray and the spreading factor and outside of the maximum distance from the point on the surface;

for each ray, if the closest intersection is in the range of the threshold, then blending shading information produced for the detected intersection with information from samples taken of the 3-D grid of volume elements that are within the range of the threshold; and

producing shading information for the point on the surface, using one or more of shading information produced for a detected intersection and sampled light information from the 3-D grid of volume elements, wherein said shading information is used in rendering said computer graphics image.

15. The method of rendering a computer graphics image of claim 14, further comprising determining lighting characteristics of surfaces in said 3-D scene by selecting a plurality of sizes of the volume elements using the spreading factor and a distance from the origin of the ray and the respective location of the volume element for use in producing said shading information.

16. A method for use in rendering a computer graphics image from 3-D scene data comprising one or more geometrical objects, comprising:

identifying a point on a surface of an object in a 3-D scene defined by said 3-D scene data for which lighting information is to be determined;

performing, by a processor, one or more point sampling operations within a maximum distance from the point along one or more directions, to produce point sampling data;

performing, by a processor, one or more volume sampling operations in a 3-D grid of volume elements in the 3-D scene, each volume element associated with data representative of light energy propagating through a surface of that volume element, farther from the point along the direction than the maximum distance; and

using the point sampling data and data obtained from the volume sampling operations to produce a rendering output for the point, by blending the point sampling data and the data obtained from the volume sampling operations if a closest intersection is within a range of a threshold distance from the point;

wherein said rendering output is used in rendering said computer graphics image.

17. The method for use in rendering a computer graphics claim 16, further comprising defining a transition zone at an intermediate distance from the point, in which both the point sampling operations and the volume sampling operations are performed.

18. The method for use in rendering a computer graphics claim 16, wherein each of the point sampling operations comprises tracing a ray in a direction, originating from the point, to determine whether the ray intersects geometry in the 3-D scene within the maximum distance.

19. The method for use in rendering a computer graphics claim 16, wherein the maximum distance is inversely related to a spreading factor that defines a relationship between distance from the point and an area of a section located in the 3-D scene that is used to determine which volume elements are to be sampled for each volume sampling operation.