What would be the value of VkAccessFlags for a VkBuffer or VkImage after being allocated memory?

Question

So I create a bunch of buffers and images, and I need to set up a memory barrier for some reason.

How do I know what to specify in the srcAccessMask field for the barrier struct of a newly created buffer or image, seeing as at that point I wouldn't have specified the access flags for it? How do I decide what initial access flags to specify for the first memory barrier applied to a buffer or image?

Specifying initial values for other parameters in Vk*MemoryBarrier is easy since I can clearly know, say, the original layout of an image, but it isn't apparent to me what the value of srcAccessMask could be the first time I set up a barrier.

Is it based on the usage flags specified during creation of the object concerned? Or is there some other way that can be used to find out?

Answer 1

So, let's assume vkCreateImage and VK_LAYOUT_UNDEFINED.

Nowhere the specification says it defines some scheduled operation. So it is healthy to assume all its work is done as soon as it returns. Plus, it does not even have memory.

So any synchronization needs would be of the memory you bind to it. Let's assume it is just fresh memory from vkAllocate. Similarly, nowhere it is said in the specification that it defines some scheduled operation.

Even so, there's really only two options. Either the implementation does nothing with the memory, or it null-fills it (for security reason). In the case it null-fills it, that must be done in a way you cannot access the original data (even using synchronization errors). So it is healthy to assume the memory has no "synchronization baggage" on it.

So simply srcStageMask = VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT (no previous outstanding scheduled operation) and srcAccessMask = 0 (no previous writes) should be correct.