Intersection testing in a ray tracing system using offset intersection distances
A method and an intersection testing module for performing intersection testing in a ray tracing system determines a first offset intersection distance which is equal to a sum of an intersection distance at which a ray intersects a first primitive and a first offset which is dependent upon the orientation of the first primitive. A second offset intersection distance is determined which is equal to a sum of an intersection distance at which the ray intersects a second primitive and a second offset which is dependent upon the orientation of the second primitive. The determined first and second offset intersection distances are compared to select the intersection of the ray with one of the first and second primitives.
1 . A computer-implemented method of performing intersection testing in a ray tracing system, the method comprising:
determining a first offset intersection distance which is equal to a sum of an intersection distance at which a ray intersects a first primitive and a first offset which is dependent upon the orientation of the first primitive;
determining a second offset intersection distance which is equal to a sum of an intersection distance at which the ray intersects a second primitive and a second offset which is dependent upon the orientation of the second primitive; and
comparing the determined first and second offset intersection distances to select the intersection of the ray with one of the first and second primitives.
2 . The method of claim 1 , wherein said determining the first offset intersection distance comprises determining the intersection distance at which the ray intersects the first primitive, and wherein said determining the second offset intersection distance comprises determining the intersection distance at which the ray intersects the second primitive.
3 . The method of claim 2 , wherein said determining the first offset intersection distance comprises offsetting the determined intersection distance at which the ray intersects the first primitive by the first offset.
4 . The method of claim 2 , wherein said determining the second offset intersection distance comprises offsetting the determined intersection distance at which the ray intersects the second primitive by the second offset.
5 . The method of claim 1 , wherein the orientation of the first primitive is different to the orientation of the second primitive, and wherein the first offset is different to the second offset.
6 . The method of claim 5 , wherein the first offset is zero and the second offset is non-zero.
7 . The method of claim 5 , wherein the second offset is zero and the first offset is non-zero.
8 . The method of claim 1 , wherein if the first offset is non-zero, then an offset with the same sign as the first offset is used for determining offset intersection distances for any primitives which have the same orientation as the first primitive, and
wherein if the second offset is non-zero, then an offset with the same sign as the second offset is used for determining offset intersection distances for any primitives which have the same orientation as the second primitive.
9 . The method of claim 1 , wherein if the first offset is non-zero, then an offset with the same sign and mantissa as the first offset is used for determining offset intersection distances for any primitives which have the same orientation as the first primitive;
wherein if the second offset is non-zero, then an offset with the same sign and mantissa as the second offset is used for determining offset intersection distances for any primitives which have the same orientation as the second primitive; and
wherein each of the offsets has an exponent which scales with an exponent of the intersection distance with which it is to be summed.
10 . The method of claim 1 , wherein if the first offset is non-zero, then an offset with the same sign, mantissa and exponent as the first offset is used for determining offset intersection distances for any primitives which have the same orientation as the first primitive, and
wherein if the second offset is non-zero, then an offset with the same sign, mantissa and exponent as the second offset is used for determining offset intersection distances for any primitives which have the same orientation as the second primitive.
11 . The method of claim 1 , wherein
if the first primitive has a particular orientation then the first offset is less than if the first primitive does not have the particular orientation, and
if the second primitive has the particular orientation then the second offset is less than if the second primitive does not have the particular orientation.
12 . The method of claim 1 , wherein said comparing the determined first and second offset intersection distances comprises identifying which of the determined first and second offset intersection distances is lower, wherein the intersection corresponding to the identified offset intersection distance is selected.
13 . The method of claim 11 , wherein a primitive which has said particular orientation is a front-facing primitive, and wherein a primitive which has an orientation that is different to said particular orientation is a back-facing primitive.
14 . The method of claim 1 , further comprising determining that the ray intersects the first and second primitives.
15 . The method of claim 1 , wherein if the determined first and second offset intersection distances are equal, the intersection of the ray with one of the first and second primitives is selected based on unique primitive IDs which are associated with the first and second primitives.
16 . The method of claim 1 , further comprising using the selected intersection in the ray tracing system for rendering an image.
17 . An intersection testing module, for use in a ray tracing system, the intersection testing module comprising:
intersection selection logic configured to:
determine a first offset intersection distance which is equal to a sum of an intersection distance at which a ray intersects a first primitive and a first offset which is dependent upon the orientation of the first primitive;
determine a second offset intersection distance which is equal to a sum of an intersection distance at which the ray intersects a second primitive and a second offset which is dependent upon the orientation of the second primitive; and
compare the determined first and second offset intersection distances to select the intersection of the ray with one of the first and second primitives.
18 . The intersection testing module of claim 17 , further comprising intersection determination logic configured to:
determine that the ray intersects the first primitive and determine the intersection distance at which the ray intersects the first primitive; and
determine that the ray intersects the second primitive and determine the intersection distance at which the ray intersects the second primitive.
19 . The intersection testing module of claim 17 , wherein the intersection selection logic is configured to compare the determined first and second offset intersection distances to select the intersection of the ray with one of the first and second primitives by identifying which of the determined first and second offset intersection distances is lower, wherein the intersection corresponding to the identified offset intersection distance is selected.
20 . A non-transitory computer readable storage medium having stored thereon an integrated circuit definition dataset that, when processed in an integrated circuit manufacturing system, configures the integrated circuit manufacturing system to manufacture an intersection testing module for use in a ray tracing system, the intersection testing module comprising:
intersection selection logic configured to:
determine a first offset intersection distance which is equal to a sum of an intersection distance at which a ray intersects a first primitive and a first offset which is dependent upon the orientation of the first primitive;
determine a second offset intersection distance which is equal to a sum of an intersection distance at which the ray intersects a second primitive and a second offset which is dependent upon the orientation of the second primitive; and
compare the determined first and second offset intersection distances to select the intersection of the ray with one of the first and second primitives.