Fix variable count descriptor set allocations (#1702)

* fix variable count descriptor set allocations

* remove option

vulkano/src/descriptor_set/layout/sys.rs

@@ -33,6 +33,8 @@ pub struct DescriptorSetLayout {
     desc: DescriptorSetDesc,
     // Number of descriptors.
     descriptors_count: DescriptorsCount,
+    // Number of descriptors in a variable count descriptor. Will be zero if no variable count descriptors are present.
+    variable_descriptor_count: u32,
 }
 
 impl DescriptorSetLayout {
@@ -50,6 +52,7 @@ impl DescriptorSetLayout {
     {
         let desc = desc.into();
         let mut descriptors_count = DescriptorsCount::zero();
+        let mut variable_descriptor_count = 0;
         let bindings = desc.bindings();
         let mut bindings_vk = Vec::with_capacity(bindings.len());
         let mut binding_flags_vk = Vec::with_capacity(bindings.len());
@@ -130,6 +133,7 @@ impl DescriptorSetLayout {
                     ));
                 }
 
+                variable_descriptor_count = desc.descriptor_count;
                 // TODO: should these be settable separately by the user?
                 binding_flags |= ash::vk::DescriptorBindingFlags::VARIABLE_DESCRIPTOR_COUNT;
                 binding_flags |= ash::vk::DescriptorBindingFlags::PARTIALLY_BOUND;
@@ -191,6 +195,7 @@ impl DescriptorSetLayout {
             device,
             desc,
             descriptors_count,
+            variable_descriptor_count,
         })
     }
 
@@ -204,6 +209,12 @@ impl DescriptorSetLayout {
         &self.descriptors_count
     }
 
+    /// Returns the number of descriptors in a variable count descriptor. This will return zero if there are no variable count descriptors present.
+    #[inline]
+    pub fn variable_descriptor_count(&self) -> u32 {
+        self.variable_descriptor_count
+    }
+
     /// Returns the number of binding slots in the set.
     #[inline]
     pub fn num_bindings(&self) -> u32 {

vulkano/src/descriptor_set/pool/sys.rs

@@ -157,6 +157,8 @@ impl UnsafeDescriptorPool {
     where
         I: IntoIterator<Item = &'l DescriptorSetLayout>,
     {
+        let mut variable_descriptor_counts: SmallVec<[_; 8]> = SmallVec::new();
+        
         let layouts: SmallVec<[_; 8]> = layouts
             .into_iter()
             .map(|l| {
@@ -166,17 +168,20 @@ impl UnsafeDescriptorPool {
                     "Tried to allocate from a pool with a set layout of a different \
                                  device"
                 );
+
+                variable_descriptor_counts.push(l.variable_descriptor_count());
                 l.internal_object()
             })
             .collect();
 
-        self.alloc_impl(&layouts)
+        self.alloc_impl(&layouts, &variable_descriptor_counts)
     }
 
     // Actual implementation of `alloc`. Separated so that it is not inlined.
     unsafe fn alloc_impl(
         &mut self,
         layouts: &SmallVec<[ash::vk::DescriptorSetLayout; 8]>,
+        variable_descriptor_counts: &SmallVec<[u32; 8]>,
     ) -> Result<UnsafeDescriptorPoolAllocIter, DescriptorPoolAllocError> {
         let num = layouts.len();
 
@@ -186,10 +191,25 @@ impl UnsafeDescriptorPool {
             });
         }
 
+        let variable_desc_count_alloc_info = if variable_descriptor_counts.iter().any(|c| *c != 0) {
+            Some(ash::vk::DescriptorSetVariableDescriptorCountAllocateInfo {
+                descriptor_set_count: layouts.len() as u32,
+                p_descriptor_counts: variable_descriptor_counts.as_ptr(),
+                .. Default::default()
+            })
+        } else {
+            None
+        };
+
         let infos = ash::vk::DescriptorSetAllocateInfo {
             descriptor_pool: self.pool,
             descriptor_set_count: layouts.len() as u32,
             p_set_layouts: layouts.as_ptr(),
+            p_next: if let Some(next) = variable_desc_count_alloc_info.as_ref() {
+                next as *const _ as *const _
+            } else {
+                ptr::null()
+            },
             ..Default::default()
         };