Compressed ray direction data in a ray tracing system

A ray compression method comprising:

• obtaining ray direction data for a ray to be processed in a ray tracing system, the ray direction data comprising three components representing a direction of the ray in the three-dimensional space of a scene to be rendered;
• compressing the ray direction data for the ray in accordance with an octahedral vector format which uses two parameters to reference a position on an octahedron to represent the ray direction;
• scaling a clipping distance of the ray by transforming the clipping distance for the ray into Manhattan space;
• storing the compressed ray direction data for the ray in a memory for subsequent use in performing intersection testing on the ray;
• and
• storing the scaled clipping distance of the ray.

A method of processing data in a ray tracing system, the method comprising:

• executing a shader program which outputs a ray for intersection testing;
• compressing ray direction data for the ray;
• storing the compressed ray direction data;
• scaling a clipping distance of the ray by an amount based on the magnitude of an unnormalised ray direction vector for the ray, wherein the unnormalised ray direction vector is a projection of an uncompressed ray direction vector for the ray onto an octahedron;
• storing the scaled clipping distance of the ray;
• and
• performing intersection testing on the ray without fully decompressing the compressed ray direction data,
• wherein the ray tracing system is configured to use results of the intersection testing for rendering the image of the scene.