C# DllImport : AccessViolationException when calling a vkCreateInstance

Question

I'm trying to create a Vulkan wrapper in C#, but I have some problems when I call a function. I rewrote the vulkan.h header as follows :

public static class Vk {
    [StructLayout(LayoutKind.Sequential)] public class Instance { }

    public enum Result {
        ...
    }
    public enum StructureType {
        ...
    }

    [StructLayout(LayoutKind.Sequential)] public class ApplicationInfo {
        public StructureType sType;
        public IntPtr pNext;
        public string pApplicationName;
        public uint applicationVersion;
        public string pEngineName;
        public uint engineVersion;
        public uint apiVersion;
    }

    [StructLayout(LayoutKind.Sequential)] public class InstanceCreateInfo {
        public StructureType sType;
        public IntPtr pNext;
        public uint flags_VkInstanceCreateFlags;
        public ApplicationInfo pApplicationInfo;
        public uint enabledLayerCount;
        public string[] ppEnabledLayerNames;
        public uint enabledExtensionCount;
        public string[] ppEnabledExtensionNames;
    }

    [DllImport("vulkan-1.dll", EntryPoint = "vkCreateInstance")]
    public extern static Result CreateInstance(
        InstanceCreateInfo pCreateInfo,
        IntPtr AllocationCallbacks_pAllocator,
        out IntPtr pInstance_Instance);
}

The original declaration in C of this function is

VKAPI_ATTR VkResult VKAPI_CALL vkCreateInstance(
    const VkInstanceCreateInfo*                 pCreateInfo,
    const VkAllocationCallbacks*                pAllocator,
    VkInstance*                                 pInstance);

Now when I call my function, I'm doing like this :

Vk.InstanceCreateInfo instance_create_info = new Vk.InstanceCreateInfo();
...

IntPtr hinstance;
Vk.Result result = Vk.CreateInstance(instance_create_info, IntPtr.Zero, out hinstance);   <-- error AccessViolationException

I don't understand where is my problem, because it seems to be a valid solution : StackOverflow : AccessViolationException when calling vkEnumeratePhysicalDevices via pInvoke from c#.

I tried by initializing my IntPtr hinstance with

Marshal.AllocHGlobal(Marshal.SizeOf<Vk.Instance>());

I also tried to "convert" my instance_create_info to another IntPtr with Marshal.StructureToPtr(...); and I tried to pass instance_create_info and instance by the ref keyword. Obviously, nothing worked.

Any idea ?

EDIT :

The native function is used as follows :

//Definition
typedef struct VkApplicationInfo {
    VkStructureType    sType;
    const void*        pNext;
    const char*        pApplicationName;
    uint32_t           applicationVersion;
    const char*        pEngineName;
    uint32_t           engineVersion;
    uint32_t           apiVersion;
} VkApplicationInfo;`
typedef struct VkInstanceCreateInfo {
    VkStructureType             sType;
    const void*                 pNext;
    VkInstanceCreateFlags       flags;
    const VkApplicationInfo*    pApplicationInfo;
    uint32_t                    enabledLayerCount;
    const char* const*          ppEnabledLayerNames;
    uint32_t                    enabledExtensionCount;
    const char* const*          ppEnabledExtensionNames;
} VkInstanceCreateInfo;

#define VK_DEFINE_HANDLE(object) typedef struct object##_T* object;
VK_DEFINE_HANDLE(VkInstance)

//Code
VkApplicationInfo application_info{};
    application_info.sType                  = VK_STRUCTURE_TYPE_APPLICATION_INFO;
    application_info.apiVersion             = VK_API_VERSION;
    application_info.applicationVersion     = VK_MAKE_VERSION( 1, 0, 0 );
    application_info.pApplicationName       = "";
    application_info.engineVersion          = VK_MAKE_VERSION( 1, 0, 0 );
    application_info.pEngineName            = "";

VkInstanceCreateInfo instance_create_info{};
    instance_create_info.sType                      = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
    instance_create_info.pApplicationInfo           = &application_info;
    instance_create_info.enabledLayerCount          = 0
    instance_create_info.ppEnabledLayerNames        = nullptr
    instance_create_info.enabledExtensionCount      = 0
    instance_create_info.ppEnabledExtensionNames    = nullptr

VkInstance _instance = nullptr;
assert( !vkCreateInstance( &instance_create_info, nullptr, &_instance ) );

There's not enough info here to answer. We'd need both sides of the interface in full and a spec of the semantics. Or some example C calling code. — David Heffernan, Apr 16 '16 at 15:17
@DavidHeffernan I added a sample code. Tell me if you need something else. — Clematrics, Apr 16 '16 at 15:44
I don't know how the the C# FFI works, but `out IntPtr pInstance_Instance` looks wrong. The out argument of `vkCreateInstance` takes a double-pointer to an opaque struct; an integer may not be large enough for the pointer. — Colonel Thirty Two, Apr 17 '16 at 15:51

score 1 · Accepted Answer · answered May 06 '16 at 09:11

it seems that you are trying to do something similar this guy made a wrapper for the c#. Can be useful for you. Go to Source/SharpVulkan/Generated/Functions.

    public static unsafe Instance CreateInstance(ref InstanceCreateInfo createInfo, AllocationCallbacks* allocator = null)
    {
        Instance instance;
        fixed (InstanceCreateInfo* __createInfo__ = &createInfo)
        {
            vkCreateInstance(__createInfo__, allocator, &instance).CheckError();
        }
        return instance;
    }

    [DllImport("vulkan-1.dll", CallingConvention = CallingConvention.StdCall)]
    internal static extern unsafe Result vkCreateInstance(InstanceCreateInfo* createInfo, AllocationCallbacks* allocator, Instance* instance);

    internal static unsafe void EnumerateInstanceExtensionProperties(byte* layerName, ref uint propertyCount, ExtensionProperties* properties)
    {
        fixed (uint* __propertyCount__ = &propertyCount)
        {
            vkEnumerateInstanceExtensionProperties(layerName, __propertyCount__, properties).CheckError();
        }
    }

Hope it is helpfull :)

mehrdad safa · Answer 2 · 2016-04-16T16:23:29.480

-1

remove out keyword for third argument or declare it as corresponding struct.

edited Apr 16 '16 at 16:23

answered Apr 16 '16 at 14:33

mehrdad safa

1,081
9
10

First arg is a class, so passed by ref, -1 – David Heffernan Apr 16 '16 at 15:18
@David Heffernan oh my god! that was a mistake, thank you very much. I edited the post. – mehrdad safa Apr 16 '16 at 15:23
It's still wrong though, `ref` is incorrect since that would be a reference to a reference. – David Heffernan Apr 16 '16 at 15:39
@Clematrics You've now reached the stage where you will try any combination of possibilities, almost at random, hoping for success. Isn't it better for you to understand what you are doing? – David Heffernan Apr 16 '16 at 15:40
@DavidHeffernan I prefer indeed to understand what am I doing. – Clematrics Apr 16 '16 at 15:48

C# DllImport : AccessViolationException when calling a vkCreateInstance

2 Answers2