extensions/nv/low_latency2: Use count parameter for p_timings "ar…

…ray" member

As it turns out this extension has a rather suboptimal layout where
the `vk::GetLatencyMarkerInfoNV` struct is not aware that its own
`p_timings` field is an array, because it does not have a count field.
Instead the length of this array is passed around via the `pTimingCount`
pointer parameter of `get_latency_timings()`.

A couple things are needed to set this straight:
1. The struct builder must be adjusted to accept a slice (without
   storing the length anywhere...);
2. The `get_latency_timings()` wrapper function should no longer accept
   a mutable slice of `vk::GetLatencyMarkerInfoNV`, but instead accept a
   single object that contains a pointer to the array (and `p_next`...);
3. This function must have a separate parameter to pass the length of
   the `p_timings` slice mentioned at 1., as we cannot reconstruct it
   from `vk::GetLatencyMarkerInfoNV` nor via its `p_timings` pointer;
4. The mutable struct and initialized `p_timings` array must still be
   passed fully by the user because both `vk::GetLatencyMarkerInfoNV`
   and `vk::LatencyTimingsFrameReportNV` have a `p_next` field that the
   user could initialize to point to some extension structure that they
   desire to be filled in.  This info might also be relevant in the
   `_len()` query;
5. Asserts have been put in place to ensure correct use of this API
   with regards to `p_timings` being (not) NULL for querying the count
   or actual values, respectively.

ash/src/extensions/nv/low_latency2.rs

@@ -4,7 +4,6 @@ use crate::RawPtr;
 use crate::{Device, Instance};
 use std::ffi::CStr;
 use std::mem;
-use std::ptr;
 
 /// <https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VK_NV_low_latency2.html>
 #[derive(Clone)]
@@ -53,32 +52,43 @@ impl LowLatency2 {
         (self.fp.set_latency_marker_nv)(self.handle, swapchain, latency_marker_info)
     }
 
-    /// Retrieve the number of elements to pass to [`get_latency_timings()`][Self::get_latency_timings()]
+    /// Retrieve the number of elements to pass to [`vk::GetLatencyMarkerInfoNV::timings()`] in
+    /// [`get_latency_timings()`][Self::get_latency_timings()]
     #[inline]
-    pub unsafe fn get_latency_timings_len(&self, swapchain: vk::SwapchainKHR) -> usize {
+    pub unsafe fn get_latency_timings_len(
+        &self,
+        swapchain: vk::SwapchainKHR,
+        latency_marker_info: &mut vk::GetLatencyMarkerInfoNV<'_>,
+    ) -> usize {
+        assert!(
+            latency_marker_info.p_timings.is_null(),
+            "latency_marker_info.p_timings must be NULL in order to query its length"
+        );
         let mut count = 0;
-        (self.fp.get_latency_timings_nv)(self.handle, swapchain, &mut count, ptr::null_mut());
+        (self.fp.get_latency_timings_nv)(self.handle, swapchain, &mut count, latency_marker_info);
         count as usize
     }
 
     /// <https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/vkGetLatencyTimingsNV.html>
     ///
-    /// Call [`get_latency_timings_len()`][Self::get_latency_timings_len()] to query the number of elements to pass to `latency_marker_info`.
-    /// Be sure to [`Default::default()`]-initialize these elements and optionally set their `p_next` pointer.
+    /// Call [`get_latency_timings_len()`][Self::get_latency_timings_len()] to query the number of
+    /// elements to pass to [`vk::GetLatencyMarkerInfoNV::timings()`].
+    /// Be sure to [`Default::default()`]-initialize `timing_count` elements and optionally set their `p_next` pointer.
     #[inline]
     pub unsafe fn get_latency_timings(
         &self,
         swapchain: vk::SwapchainKHR,
-        latency_marker_info: &mut [vk::GetLatencyMarkerInfoNV<'_>],
+        timing_count: usize,
+        latency_marker_info: &mut vk::GetLatencyMarkerInfoNV<'_>,
     ) {
-        let mut count = latency_marker_info.len() as u32;
-        (self.fp.get_latency_timings_nv)(
-            self.handle,
-            swapchain,
-            &mut count,
-            latency_marker_info.as_mut_ptr(),
+        let mut count = timing_count as u32;
+        assert!(
+            !latency_marker_info.p_timings.is_null(),
+            "latency_marker_info.p_timings must be a valid pointer to an array of {} elements",
+            count
         );
-        assert_eq!(count as usize, latency_marker_info.len());
+        (self.fp.get_latency_timings_nv)(self.handle, swapchain, &mut count, latency_marker_info);
+        assert_eq!(timing_count, count as usize);
     }
 
     /// <https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/vkQueueNotifyOutOfBandNV.html>

ash/src/vk/definitions.rs

@@ -4319,8 +4319,8 @@ impl<'a> PipelineMultisampleStateCreateInfo<'a> {
         self.min_sample_shading = min_sample_shading;
         self
     }
-    #[doc = r" Sets `p_sample_mask` to `null` if the slice is empty. The mask will"]
-    #[doc = r" be treated as if it has all bits set to `1`."]
+    #[doc = r" Sets [`Self::p_sample_mask`] to [`std::ptr::null()`] if the slice is empty. The"]
+    #[doc = r" mask will be treated as if it has all bits set to `1`."]
     #[doc = r""]
     #[doc = r" See <https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VkPipelineMultisampleStateCreateInfo.html#_description>"]
     #[doc = r" for more details."]
@@ -51890,9 +51890,22 @@ unsafe impl<'a> TaggedStructure for GetLatencyMarkerInfoNV<'a> {
     const STRUCTURE_TYPE: StructureType = StructureType::GET_LATENCY_MARKER_INFO_NV;
 }
 impl<'a> GetLatencyMarkerInfoNV<'a> {
+    #[doc = r" This only sets the slice pointer. Users must manually pass the length of"]
+    #[doc = r" `timings` to [`crate::extensions::nv::LowLatency2::get_latency_timings()`]."]
+    #[doc = r""]
+    #[doc = r" [`Self::p_timings`] will be set to to [`std::ptr::null_mut()`] if the"]
+    #[doc = r" slice is empty, which is necessary to query the length of the array via"]
+    #[doc = r" [`crate::extensions::nv::LowLatency2::get_latency_timings_len()`]."]
+    #[doc = r""]
+    #[doc = r" See <https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/vkGetLatencyTimingsNV.html#_description>"]
+    #[doc = r" for more details."]
     #[inline]
-    pub fn timings(mut self, timings: &'a mut LatencyTimingsFrameReportNV<'a>) -> Self {
-        self.p_timings = timings;
+    pub fn timings(mut self, timings: &'a mut [LatencyTimingsFrameReportNV<'a>]) -> Self {
+        self.p_timings = if timings.is_empty() {
+            std::ptr::null_mut()
+        } else {
+            timings.as_mut_ptr()
+        };
         self
     }
 }

generator/src/lib.rs

@@ -1972,8 +1972,8 @@ fn derive_setters(
 
         if name == "pSampleMask" {
             return Some(quote! {
-                /// Sets `p_sample_mask` to `null` if the slice is empty. The mask will
-                /// be treated as if it has all bits set to `1`.
+                /// Sets [`Self::p_sample_mask`] to [`std::ptr::null()`] if the slice is empty. The
+                /// mask will be treated as if it has all bits set to `1`.
                 ///
                 /// See <https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VkPipelineMultisampleStateCreateInfo.html#_description>
                 /// for more details.
@@ -2004,6 +2004,32 @@ fn derive_setters(
                 });
             }
 
+            // pTimings is a dynamic array, but its length is only available as a mutable-pointer parameter in a calling function:
+            // https://github.com/KhronosGroup/Vulkan-Docs/issues/2269
+            if struct_.name == "VkGetLatencyMarkerInfoNV" && field.name.as_deref() == Some("pTimings") {
+                return Some(quote! {
+                    /// This only sets the slice pointer. Users must manually pass the length of
+                    /// `timings` to [`crate::extensions::nv::LowLatency2::get_latency_timings()`].
+                    ///
+                    /// [`Self::p_timings`] will be set to to [`std::ptr::null_mut()`] if the
+                    /// slice is empty, which is necessary to query the length of the array via
+                    /// [`crate::extensions::nv::LowLatency2::get_latency_timings_len()`].
+                    ///
+                    /// See <https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/vkGetLatencyTimingsNV.html#_description>
+                    /// for more details.
+                    #[inline]
+                    #deprecated
+                    pub fn timings(mut self, timings: &'a mut [LatencyTimingsFrameReportNV<'a>]) -> Self {
+                        self.p_timings = if timings.is_empty() {
+                            std::ptr::null_mut()
+                        } else {
+                            timings.as_mut_ptr()
+                        };
+                        self
+                    }
+                });
+            }
+
             if matches!(field.array, Some(vkxml::ArrayType::Dynamic)) {
                 if let Some(ref array_size) = field.size {
                     let mut slice_param_ty_tokens = field.safe_type_tokens(quote!('a), type_lifetime.clone(), None);