Image rendering using ray-tracing

1. A method of rendering an image, the method comprising:

generating a virtual scene comprising a set of virtual resources, the virtual resources being virtual objects and/or virtual light sources;

pre-processing the virtual scene by ray-tracing with respect to a virtual camera position to detect one or more virtual resources not required for ray-tracing rendering of at least an aspect of rendering the image; and

rendering the image by a ray-tracing process from the virtual camera position, the ray-tracing process being configured to omit ray-tracing for at least a given aspect of the image, with respect to the one or more virtual resources not required for ray-tracing rendering of at least the given aspect of the image, wherein:

the pre-processing step comprises: (i) detecting, for each virtual light source, virtual objects which may be intersected by a ray emanating from that virtual light source, and (ii) storing BVH data indicative of any BVH nodes which are intersected by a ray emanating from that virtual light source;

the generating step comprises generating a bounding volume hierarchy, BVH, defining bounding volumes around the virtual objects of the set of virtual resources; and

the rendering step comprises: (i) for a given point of intersection of a ray with a given virtual object, emanating rays from that point, (ii) detecting any virtual light sources intersected by those rays, and (iii) omitting from the detection any light source not indicated by the stored BVH data, not to intersect the BVH node containing the given virtual object.

2. The method of claim 1 , in which the pre-processing step is configured to detect one or more virtual resources not required for ray-tracing rendering from that virtual camera position by detecting, using ray-tracing, whether one or more virtual resources are visible from that virtual camera position.

3. The method of claim 2 , in which the ray-tracing of the pre-processing step employs a lower density of rays than the ray-tracing of the rendering step.

4. The method of claim 2 , in which the pre-processing step comprises storing visibility data indicating of any virtual resources which are visible from the virtual camera location.

5. The method of claim 4 , in which the rendering step comprises performing the ray-tracing process in respect of those virtual resources indicated by the stored visibility data to be visible from the virtual camera location.

6. The method of claim 1 , in which each lowest level leaf node of the BVH defines a bounding volume around a single respective virtual object, and higher level nodes of the BVH define bounding volumes around respective groups of virtual objects.

7. The method of claim 6 , in which the pre-processing step comprises detecting, for each virtual light source, BVH nodes at a level higher than the leaf nodes which are intersected by a ray emanating from that virtual light source.

8. A non-transitory, machine-readable storage medium which stores computer software which, when executed by a computer, causes the computer to perform a method of rendering an image, the method comprising:

generating a virtual scene comprising a set of virtual resources, the virtual resources being virtual objects and/or virtual light sources;

pre-processing the virtual scene by ray-tracing with respect to a virtual camera position to detect one or more virtual resources not required for ray-tracing rendering of at least an aspect of rendering the image; and

rendering the image by a ray-tracing process from the virtual camera position, the ray-tracing process being configured to omit ray-tracing for at least a given aspect of the image, with respect to the one or more virtual resources not required for ray-tracing rendering of at least the given aspect of the image, wherein:

the pre-processing step comprises: (i) detecting, for each virtual light source, virtual objects which may be intersected by a ray emanating from that virtual light source, and (ii) storing BVH data indicative of any BVH nodes which are intersected by a ray emanating from that virtual light source;

the generating step comprises generating a bounding volume hierarchy, BVH, defining bounding volumes around the virtual objects of the set of virtual resources; and

the rendering step comprises: (i) for a given point of intersection of a ray with a given virtual object, emanating rays from that point, (ii) detecting any virtual light sources intersected by those rays, and (iii) omitting from the detection any light source not indicated by the stored BVH data, not to intersect the BVH node containing the given virtual object.

9. An apparatus comprising:

an image rendering apparatus, including:

a generator configured to generate a virtual scene comprising a set of virtual resources, the virtual resources being virtual objects and/or virtual light sources;

a pre-processor configured to pre-process the virtual scene by ray-tracing with respect to a virtual camera position to detect one or more virtual resources not required for ray-tracing rendering of at least an aspect of rendering the image; and

a renderer configured to render the image by a ray-tracing process from the virtual camera position, the ray-tracing process being configured to omit ray-tracing for at least a given aspect of the image, with respect to the one or more virtual resources not required for ray-tracing rendering of at least the given aspect of the image, wherein:

the pre-processor operates to: (i) detect, for each virtual light source, virtual objects which may be intersected by a ray emanating from that virtual light source, and (ii) store BVH data indicative of any BVH nodes which are intersected by a ray emanating from that virtual light source;

the generator operates to generate a bounding volume hierarchy, BVH, defining bounding volumes around the virtual objects of the set of virtual resources;

the renderer operates to: (i) for a given point of intersection of a ray with a given virtual object, emanating rays from that point, (ii) detecting any virtual light sources intersected by those rays, and (iii) omitting from the detection any light source not indicated by the stored BVH data, not to intersect the BVH node containing the given virtual object.

10. The apparatus of claim 9 , wherein the apparatus is a video game apparatus.