Support for external allocators:

* The newly introduced API surface area matches that of VMA's advanced usage and another hand-rolled memory allocator in a content-heavy application.
* All suballocator callbacks -- allocate, bind image, bind buffer, map, unmap and free -- are expected to guard VkDeviceMemory operations within a mutex.
* Each texture now also keeps track of its VkDeviceMemory offset.
* The 64 bit allocationId is to be used as a book-keeping measure by external suballocator callbacks to keep track of and free up suballocations. The external allocator can use a hashtable (ala std::unordered_map in C++) to keep track of the page(s) alloted to this suballocation. ('Pages' here refers to potential sparse bindings).

include/ktxvulkan.h

@@ -124,8 +124,22 @@ typedef struct ktxVulkanTexture
  uint32_t depth; /*!< The depth of the image. */
  uint32_t levelCount; /*!< The number of MIP levels in the image. */
  uint32_t layerCount; /*!< The number of array layers in the image. */
+ uint64_t devMemoryOffset;
+ uint64_t allocationId;
 } ktxVulkanTexture;
 
+typedef uint64_t(*subAllocatorAllocMemFuncPtr)(VkMemoryAllocateInfo* allocInfo, VkMemoryRequirements* memReq, VkDeviceMemory* devMemory, uint64_t* devMemoryOffset);
+typedef VkResult(*subAllocatorBindBufferFuncPtr)(VkBuffer buffer, uint64_t allocId);
+typedef VkResult(*subAllocatorBindImageFuncPtr)(VkImage image, uint64_t allocId);
+typedef VkResult(*subAllocatorMemoryMapFuncPtr)(uint64_t allocId, VkDeviceSize offsetFromOffset, VkDeviceSize len, void** dataPtr);
+typedef void (*subAllocatorMemoryUnmapFuncPtr)(uint64_t allocId);
+typedef void (*subAllocatorFreeMemFuncPtr)(uint64_t allocId);
+
+KTX_API void KTX_APIENTRY
+ktxVulkanTexture_Destruct_WithPotentialSuballocator(ktxVulkanTexture* This, VkDevice device,
+ const VkAllocationCallbacks* pAllocator,
+ subAllocatorFreeMemFuncPtr freeMemFuncPtr);
+
 KTX_API void KTX_APIENTRY
 ktxVulkanTexture_Destruct(ktxVulkanTexture* This, VkDevice device,
  const VkAllocationCallbacks* pAllocator);
@@ -208,6 +222,18 @@ ktxVulkanDeviceInfo_Destruct(ktxVulkanDeviceInfo* This);
 KTX_API void KTX_APIENTRY
 ktxVulkanDeviceInfo_Destroy(ktxVulkanDeviceInfo* This);
 KTX_API KTX_error_code KTX_APIENTRY
+ktxTexture_VkUploadEx_WithPotentialSuballocator(ktxTexture* This, ktxVulkanDeviceInfo* vdi,
+ ktxVulkanTexture* vkTexture,
+ VkImageTiling tiling,
+ VkImageUsageFlags usageFlags,
+ VkImageLayout finalLayout,
+ subAllocatorAllocMemFuncPtr allocMemFuncPtr,
+ subAllocatorBindBufferFuncPtr bindBufferFuncPtr,
+ subAllocatorBindImageFuncPtr bindImageFuncPtr,
+ subAllocatorMemoryMapFuncPtr memoryMapFuncPtr,
+ subAllocatorMemoryUnmapFuncPtr memoryUnmapFuncPtr,
+ subAllocatorFreeMemFuncPtr freeMemFuncPtr);
+KTX_API KTX_error_code KTX_APIENTRY
 ktxTexture_VkUploadEx(ktxTexture* This, ktxVulkanDeviceInfo* vdi,
  ktxVulkanTexture* vkTexture,
  VkImageTiling tiling,