Methods and apparatus for modifying a bounding volume hierarchy for raytracing

1. A system for performing a raytracing process, the system comprising:

a bounding volume hierarchy, BVH, identification unit operable to identify a BVH structure for use in generating images of a virtual environment, the BVH structure comprising information about one or more surfaces within the virtual environment, the information including information identifying a grouping of the one or more surfaces in dependence upon one or more surface orientations;

a BVH selection unit operable to discard, prior to a traversal of the BVH structure, one or more elements of the BVH structure in dependence upon a direction of an incident ray; and

a raytracing unit operable to perform a raytracing process using the remaining BVH elements, wherein:

the BVH selection unit is operable to discard one or more BVH elements that correspond to surfaces of an orientation that shares at least a first vector component sign as the incident ray,

each of one or more groups resulting from the grouping of the one or more surfaces corresponds to a face of a three-dimensional shape, and

each surface is assigned to group corresponding to the face that has a surface normal that most closely approximates that of the surface.

2. The system of claim 1 , wherein:

the BVH structure comprises a single BVH with a plurality of nodes each corresponding to surfaces of a respective orientation or range of orientations, and

the BVH selection unit is operable to discard one or more nodes of the BVH.

3. The system of claim 1 , wherein:

the BVH structure comprises a plurality of BVHs each corresponding to surfaces of a respective orientation or range of orientations, and

the BVH selection unit is operable to discard one or more BVHs.

4. The system of claim 3 , wherein two or more of the plurality of BVHs share one or more nodes.

5. The system of claim 1 , wherein the BVH selection unit is operable to determine a group of BVH elements to be used for raytracing in dependence upon the direction of the incident ray.

6. The system of claim 1 , wherein the three-dimensional shape is a cube.

7. A system for generating a bounding volume hierarchy, BVH, structure for use in a raytracing process, the system comprising:

a surface identification unit operable to identify one or more surfaces within a virtual environment;

a surface grouping unit operable to generate one or more groups of surfaces in dependence upon an identified surface orientation; and

a BVH structure generating unit operable to generate the BVH in dependence upon the generated grouping, wherein:

the BVH structure comprises one or more elements, and information about the one or more surfaces, the information including information identifying a grouping of the one or more surfaces in dependence upon one or more surface orientations,

each of one or more groups resulting from the grouping of the one or more surfaces corresponds to a face of a three-dimensional shape, and

each surface is assigned to group corresponding to the face that has a surface normal that most closely approximates that of the surface.

8. A method for generating images, the method comprising:

identifying a bounding volume hierarchy, BVH, structure for use in generating images of a virtual environment, the BVH structure comprising information about one or more surfaces within the virtual environment, the information including information identifying a grouping of the one or more surfaces in dependence upon one or more surface orientations;

discarding, prior to a traversal of the BVH structure, one or more elements of the BVH structure in dependence upon a direction of an incident ray; and

performing a raytracing process using the remaining BVH elements, wherein:

each of one or more groups resulting from the grouping of the one or more surfaces corresponds to a face of a three-dimensional shape, and

each surface is assigned to group corresponding to the face that has a surface normal that most closely approximates that of the surface.

9. A method for generating a bounding volume hierarchy, BVH, structure for use in a raytracing process, the method comprising:

identifying one or more surfaces within a virtual environment;

generating one or more groups of surfaces in dependence upon an identified surface orientation; and

generating the BVH in dependence upon the generated grouping, wherein:

the BVH structure comprises one or more elements, and information about the one or more surfaces, the information including information identifying a grouping of the one or more surfaces in dependence upon one or more surface orientations,

each of one or more groups resulting from the grouping of the one or more surfaces corresponds to a face of a three-dimensional shape, and

each surface is assigned to group corresponding to the face that has a surface normal that most closely approximates that of the surface.

10. A non-transitory machine-readable storage medium which stores computer software which, when executed by a computer, causes the computer to perform a method for generating a bounding volume hierarchy, BVH, structure for use in a raytracing process, the method comprising:

identifying one or more surfaces within a virtual environment;

generating one or more groups of surfaces in dependence upon an identified surface orientation; and

generating the BVH in dependence upon the generated grouping, wherein:

the BVH structure comprises one or more elements, and information about the one or more surfaces, the information including information identifying a grouping of the one or more surfaces in dependence upon one or more surface orientations,

each of one or more groups resulting from the grouping of the one or more surfaces corresponds to a face of a three-dimensional shape, and

each surface is assigned to group corresponding to the face that has a surface normal that most closely approximates that of the surface.