Exit early when importing a resource without allocation.

Author: bbernhar

include/gpgmm_d3d12.h

@@ -1113,11 +1113,11 @@ namespace gpgmm::d3d12 {
                                        const D3D12_CLEAR_VALUE* pClearValue,
                                        IResourceAllocation** ppResourceAllocationOut) = 0;
 
-        /** \brief  Imports an existing D3D12 resource.
+        /** \brief  Use existing D3D12 resource as a resource allocation.
 
-        Allows externally created D3D12 resources to be used as a ResourceAllocation.
+        Returns a ResourceAllocation which represents an existing resource with a resource heap.
 
-        @param allocationDescriptor A reference to ALLOCATION_DESC structure that provides
+        @param allocationDescriptor A reference to ALLOCATION_DESC structure that provides.
         properties for the resource allocation.
         @param pCommittedResource A pointer to a committed ID3D12Resource.
         @param[out] ppResourceAllocationOut Pointer to a memory block that receives a pointer to the

src/gpgmm/d3d12/ResourceAllocatorD3D12.cpp

@@ -1305,6 +1305,11 @@ namespace gpgmm::d3d12 {
             return E_INVALIDARG;
         }
 
+        // If no resource allocation is to be created then only validate by returning early.
+        if (ppResourceAllocationOut == nullptr) {
+            return S_FALSE;
+        }
+
         HEAP_DESC resourceHeapDesc = {};
         resourceHeapDesc.SizeInBytes = resourceInfo.SizeInBytes;
         resourceHeapDesc.Alignment = resourceInfo.Alignment;
@@ -1328,13 +1333,10 @@ namespace gpgmm::d3d12 {
         allocationDesc.HeapOffset = kInvalidSize;
         allocationDesc.SizeInBytes = allocationSize;
         allocationDesc.Method = AllocationMethod::kStandalone;
-        allocationDesc.OffsetFromResource = 0;
 
-        if (ppResourceAllocationOut != nullptr) {
-            *ppResourceAllocationOut = new ResourceAllocation(
-                allocationDesc, nullptr, this, static_cast<Heap*>(resourceHeap.Detach()), nullptr,
-                std::move(resource));
-        }
+        *ppResourceAllocationOut = new ResourceAllocation(allocationDesc, nullptr, this,
+                                                          static_cast<Heap*>(resourceHeap.Detach()),
+                                                          nullptr, std::move(resource));
 
         return S_OK;
     }