get_query_pool_results buggy when called with vk::QueryResultFlags::WITH_AVAILABILITY

[matszczygiel]

Hello,
I have a piece of code which according to my knowledge does not violate the Vulkan spec.

let first_query = 0;
let query_count = 2;
let flags = vk::QueryResultFlags::WITH_AVAILABILITY;
let mut data = [0u32; 4];
device.get_query_pool_results(
    query_pool,
    first_query,
    query_count,
    data.as_mut_slice(),
    flags,
)?;

This code gives a validation error:

[VK][Validation]"Validation Error: [ VUID-vkGetQueryPoolResults-dataSize-00817 ] Object 0: handle = 0x13105e0000000155, type = VK_OBJECT_TYPE_QUERY_POOL; | MessageID = 0x73375ed4 | vkGetQueryPoolResults() on querypool VkQueryPool 0x13105e0000000155[] specified dataSize 8 which is incompatible with the specified query type and options. The Vulkan spec states: dataSize must be large enough to contain the result of each query, as described here (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-vkGetQueryPoolResults-dataSize-00817)"

I managed to locate a bug in the implementation of this function. It passes query_count as a data length parameter forward. This is fine in most cases but here the flagvk::QueryResultFlags::WITH_AVAILABILITY requires the data to be twice as large as query_count.
I will open PR with a fix.

[MarijnS95]

This ended up not requiring a fix but merely a simplified API since the type T of data: &[T] is used to determine the stride, where T = u32 for a WITH_AVAILABILITY query would overwrite the bool in query N-1 which was not addressed by the linked PR. Instead we now force the user to use slice length by removing the query_count parameter: #644

This is a breaking change that has not been released yet (will be part of Ash 0.38) but to achieve what you want now, make sure T includes the availability flag through a tuple via T = (0u32, vk::Bool32), and request a total of 2 instead of 4 queries:

let first_query = 0;
let flags = vk::QueryResultFlags::WITH_AVAILABILITY;
let mut data = [(0u32, vk::Bool32); 2];
device.get_query_pool_results(
    query_pool,
    first_query,
    data.len(),
    data.as_mut_slice(),
    flags,
)?;

This pattern remains in Ash 0.38, where only data.len() (= query count) should be removed from the call signature.