Path guiding for path-traced rendering

1. A computer-implemented method for generating a mask for a light source used in rendering virtual scenes, the computer-implemented method comprising:

under control of one or more computer systems configured with executable instructions, perform steps of:

determining a bounding volume for a scene based on a frustum or spherical aperture of a virtual camera having a virtual camera position in the scene;

generating a path-traced first image of a portion of the scene within the bounding box by projecting a plurality of first light paths from the virtual camera position, wherein each first light path of the plurality of first light paths comprises a plurality of vertices;

storing a light paths subset of the plurality of first light paths, wherein a stored light path in the light paths subset is a light path that exits at the light source;

removing objects from the scene that are sampled less than a predetermined threshold by the first light paths to form a modified virtual scene, wherein the objects are not light paths;

generating an initial mask for the light source from the light paths subset such that at least some positions on the light source is assigned an emission probability in the initial mask based on a density of first light paths emitted from that position on the light source that exit at the virtual camera position, thereby generating a masked light source data structure wherein light paths are emitted by the light source anisotropically;

refining the initial mask, to form a refined mask, by generating successive second images of the scene by repeatedly:

(a) generating a path-traced second image using the masked light source data structure and the modified virtual scene to generate an isotropic plurality of second light paths;

(b) storing the second light paths that exit at the virtual camera position into an exiting path subset; and

(c) modifying the emission probability of the at least some positions on the light source based on a cumulative average across a plurality of the successive second images of a density of second light paths stored in the exiting path subset; and

storing the refined mask into computer memory for use in a rendering process.

2. The computer-implemented method of claim 1 , wherein the frustum comprises a truncated pyramid.

3. The computer-implemented method of claim 1 , wherein the predetermined threshold is zero samples.

4. The computer-implemented method of claim 1 , wherein the refined mask comprises a probability density function.

5. The computer-implemented method of claim 1 , further comprising:

if a termination/splitting factor is less than one, terminating a light path.

6. The computer-implemented method of claim 1 , wherein the refined mask comprises nonzero emission probability only for positions capable of emitting into the bounding volume.

7. The computer-implemented method of claim 6 , wherein the cumulative average is cumulative across at least some of the successive second images.

8. The computer-implemented method of claim 7 , wherein terminating a given light path comprises deleting selected vertices of the given light path.

9. The computer-implemented method of claim 8 , further comprising denoising the path-traced first image or a path-traced second image.

10. The computer-implemented method of claim 9 , wherein the denoising comprises employing density-based outlier rejection.

11. A computer system for modeling surfaces of simulated objects, the computer system comprising:

at least one processor; and

a computer-readable medium storing instructions, which when executed by the at least one processor, causes the computer system to carry out the method of claim 1 .

12. A non-transitory computer-readable storage medium storing instructions, which when executed by at least one processor of a computer system, causes the computer system to carry out the method of claim 1 .