Cube image specification clarification

A VkImage created with VK_IMAGE_CREATE_CUBE_COMPATIBLE_BIT can have over 6 layers. In this case, is it allowed to have overlapping cubemaps? For example, can we have a cubemap in layers [0-5] and another cubemap on in layers[1-6] or is it only legal to have cubemaps start at layers which are multiples of 6, which would mean no overlap is allowed?

This would be key for any implementation which precomputes neighboring borders for each cubemap face for texture filtering across multiple faces. Allowing overlapping cubemaps would mean that these borders could have to be modified multiple times within the same draw call, potentially impacting performance.

The issue names no file, test, or specification entry point. Review the Vulkan cube-compatible image and layer rules, determine whether overlapping cubemaps are legal, and update the relevant specification wording so the allowed layer ranges and overlap behavior are explicit.

Written by the indexing model from the issue text.