Intersection Testing in a Ray Tracing System Using Three-Dimensional Axis-Aligned Box

A method of determining, in a ray tracing system, whether a ray intersects a three-dimensional axis-aligned box, wherein the box represents a volume defined by a front-facing plane and a back-facing plane for each dimension of the three-dimensional axis-aligned box, the method comprising:

• identifying which of the back-facing planes intersects the ray as a position that is the least far along a direction of the ray;
• and
• determining whether the ray intersects the axis-aligned-box in dependence on comparing (i) the position at which the ray intersects the identified back-facing plane with (ii) at least one position at which the ray intersects one of the front-facing planes for the two dimensions for which the back-facing plane was not identified;
• wherein the method determines whether the ray intersects the box without comparing the position at which the ray intersects the identified back-facing plane with a position at which the ray intersects the front-facing plane in the dimension for which back-facing plane was identified.

An intersection testing module implemented in fixed function circuitry, for use in a ray tracing system, configured to determine whether a ray intersects a three-dimensional axis-aligned box, wherein the box represents a volume defined by a front-facing plane and a back-facing plane for each dimension of the three-dimensional axis-aligned box, the intersection testing module being configured to:

• identify which of the front-facing planes intersects the ray at a position that is furthest along a direction of the ray;
• and
• determine whether the ray intersects the axis-aligned box in dependence on comparing (i) the position at which the ray intersects the identified front-facing plane with (ii) at least one position at which the ray intersects one of the back-facing planes for the two dimensions for which the front-facing plane was not identified;
• wherein the intersection testing module is configured to determine whether the ray intersects the box without comparing the position at which the ray intersects the identified front-facing plane with a position at which the ray intersects the back-facing plane in the dimension for which the front-facing plane was identified.

An intersection testing module implemented in fixed function circuitry, for use in a ray tracing system, configured to determine whether a ray intersects a three-dimensional axis-aligned box, wherein the box represents a volume defined by a front-facing plane and a back-facing plane for each dimension of the three-dimensional axis-aligned box, the intersection testing module being configured to:

• identify which of the back-facing planes intersects the ray at a position that is the least far along a direction of the ray;
• and
• determine whether the ray intersects the axis-aligned-box in dependence on comparing (i) the position at which the ray intersects the identified back-facing plane with (ii) at least one position at which the ray intersects one of the front-facing planes for the two dimensions for which the back-facing plane was not identified;
• wherein the intersection testing module is configured to determine whether the ray intersects the box without comparing the position at which the ray intersects the identified back-facing plane with a position at which the ray intersects the front-facing plane in the dimension for which back-facing plane was identified.