This is a duplicate of my StackOverflow post linked here
I am currently working with Metal's ray tracing API. I remembered I could pass data from an intersection function to the compute kernel that started the ray intersection process. After rewatching the WWDC 2020 talk Discover ray tracing with Metal by Sean James (linked here), I found the relevant section around 16:13 where he talks about the ray payload.
However, I was curious where this payload is stored as it passed to the intersection function. When declared with the relevant [[ payload ]] attribute in the intersection function, it must be in the ray_data address. According to the Metal Shading Language Specification (version 2.3), pg. 64, the data passed into the intersection function is copied in the ray_data address space and is copied back out once the intersection function returns. However, this doesn't specify if, e.g., the data is stored in tile memory (like data in the threadgroup address space is) or stored in the per-thread memory (thread address space). The video did not specify this either.
In fact, the declarations for the intersect function (see pg. 204) that include the payload term are in the thread address space (which makes sense)
So where does the copied ray_data "version" of the data stored in the thread address space in the kernel go?
I am currently working with Metal's ray tracing API. I remembered I could pass data from an intersection function to the compute kernel that started the ray intersection process. After rewatching the WWDC 2020 talk Discover ray tracing with Metal by Sean James (linked here), I found the relevant section around 16:13 where he talks about the ray payload.
However, I was curious where this payload is stored as it passed to the intersection function. When declared with the relevant [[ payload ]] attribute in the intersection function, it must be in the ray_data address. According to the Metal Shading Language Specification (version 2.3), pg. 64, the data passed into the intersection function is copied in the ray_data address space and is copied back out once the intersection function returns. However, this doesn't specify if, e.g., the data is stored in tile memory (like data in the threadgroup address space is) or stored in the per-thread memory (thread address space). The video did not specify this either.
In fact, the declarations for the intersect function (see pg. 204) that include the payload term are in the thread address space (which makes sense)
So where does the copied ray_data "version" of the data stored in the thread address space in the kernel go?
