This is the April 2024 Update (v2.21.0) (#2115)

* Fix #2026

* Fix #2000, closes #2005

* Fix #2010

* Fix added AL bug (good thing we had tests!)

* Fix #1500

* Undo any unintentional changes

* Add nint overloads for things like VertexAttribPointer

* Fix build errors

* Add more standard cursor shapes

* Upversion natives where necessary

* Patch notes for 2.21

* Reorder literally a single line

* Incorporate #2143/#2066/#2090 in patch notes

* Implement IsExtensionPresent for WGL

* nit

* OpenXR updates?

* Fix flawed constant parsing for Vk/XR

* Add openxr to patch notes

* Update patch notes for 2.21

Silk.NET.sln

@@ -610,6 +610,12 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "HelloWorld", "examples\CSha
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Silk.NET.OpenXR.Extensions.NV", "src\OpenXR\Extensions\Silk.NET.OpenXR.Extensions.NV\Silk.NET.OpenXR.Extensions.NV.csproj", "{34D35A41-E974-40C9-8888-3510A0F074AA}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Silk.NET.OpenXR.Extensions.LEIA", "src\OpenXR\Extensions\Silk.NET.OpenXR.Extensions.LEIA\Silk.NET.OpenXR.Extensions.LEIA.csproj", "{B70533BB-FB84-4BC3-888C-88E5F40FD22D}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Silk.NET.OpenXR.Extensions.ANDROIDX", "src\OpenXR\Extensions\Silk.NET.OpenXR.Extensions.ANDROIDX\Silk.NET.OpenXR.Extensions.ANDROIDX.csproj", "{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Silk.NET.OpenXR.Extensions.ANDROIDSYS", "src\OpenXR\Extensions\Silk.NET.OpenXR.Extensions.ANDROIDSYS\Silk.NET.OpenXR.Extensions.ANDROIDSYS.csproj", "{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -3715,6 +3721,42 @@ Global
 		{34D35A41-E974-40C9-8888-3510A0F074AA}.Release|x64.Build.0 = Release|Any CPU
 		{34D35A41-E974-40C9-8888-3510A0F074AA}.Release|x86.ActiveCfg = Release|Any CPU
 		{34D35A41-E974-40C9-8888-3510A0F074AA}.Release|x86.Build.0 = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|x64.Build.0 = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Debug|x86.Build.0 = Debug|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|x64.ActiveCfg = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|x64.Build.0 = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|x86.ActiveCfg = Release|Any CPU
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D}.Release|x86.Build.0 = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|x64.Build.0 = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Debug|x86.Build.0 = Debug|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|Any CPU.Build.0 = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|x64.ActiveCfg = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|x64.Build.0 = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|x86.ActiveCfg = Release|Any CPU
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C}.Release|x86.Build.0 = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|x64.Build.0 = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Debug|x86.Build.0 = Debug|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|Any CPU.Build.0 = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|x64.ActiveCfg = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|x64.Build.0 = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|x86.ActiveCfg = Release|Any CPU
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -4012,6 +4054,9 @@ Global
 		{FD0C9C4B-3777-4755-A87B-60FE65D92750} = {6842A2C6-5C7B-42DD-9825-0EDE91BFEBF7}
 		{9CB90BB8-946F-4962-9365-A97BF5C6550A} = {FD0C9C4B-3777-4755-A87B-60FE65D92750}
 		{34D35A41-E974-40C9-8888-3510A0F074AA} = {90471225-AC23-424E-B62E-F6EC4C6ECAC0}
+		{B70533BB-FB84-4BC3-888C-88E5F40FD22D} = {90471225-AC23-424E-B62E-F6EC4C6ECAC0}
+		{25ABCA5E-4FF6-43ED-9A5E-443E1373EC5C} = {90471225-AC23-424E-B62E-F6EC4C6ECAC0}
+		{01B6FFA0-5B37-44EA-ABDF-7BABD05874C5} = {90471225-AC23-424E-B62E-F6EC4C6ECAC0}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F5273D7F-3334-48DF-94E3-41AE6816CD4D}

build/props/common.props

@@ -12,22 +12,49 @@
         <LangVersion>10</LangVersion>
         <Authors>.NET Foundation and Contributors</Authors>
         <PackageReleaseNotes>
-            Silk.NET December 2023 Update
+            Silk.NET April 2024 Update
 
-            - Added support for UTF-8 file paths in GLFW and SDL windows (thanks @WinstonMao)
-            - Updated to OpenXR 1.0.32.1
-            - Updated to Vulkan 1.3.273
-            - Updated to latest OpenGL specifications
-            - Updated to latest OpenCL specifications
-            - Fixed Matrix2X2.GetDeterminant returning incorrect values
-            - Fixed ALC_SOFT_reopen_device being a non-context extension (thanks @okaniku, @doobah)
+            - Added nint overloads for the cases where OpenGL represents a native-sized integer as a void pointer.
+            - Added support for executing Windowing loops during repaint and drag events on GLFW in some cases. (thanks @otac0n)
+            - Added a distinction between "unset" (-1) and "default" (null) for Windowing depth/stencil buffer bits, defaulting to 24/8 on all platforms unless overridden.
+            - Added support for 64-bit Arm Linux for Assimp, GLFW (+ Windowing &amp; Input), OpenAL Soft, SDL, Vkd3d, Vulkan Loader, SwiftShader, and WGPU. (thanks @alexrp)
+            - Added support for Apple Silicon Macs for OpenAL Soft, Vulkan Loader, and SwiftShader. (thanks @alexrp)
+            - Added support for 32-bit Arm Linux for Assimp, GLFW, OpenAL Soft, SDL, Shaderc, SPIR-V Cross, SPIR-V Reflect, Vkd3d, SwiftShader, and WGPU. (thanks @alexrp)
+            - Added support for 64-bit Windows on Arm for Assimp, OpenAL Soft, VulkanLoader, and SwiftShader. (thanks @alexrp)
+            - Added limited native library support (SPIR-V Tools and Shaderc) for glibc versions as old as 2.17 on Linux platforms.
+            - Added support for new standard cursor shapes in Input and GLFW.
+            - Updated to use `ref readonly` instead of `in`.
+            - Updated to OpenXR 1.1.36.
+            - Updated to DirectStorage 1.2.2.
+            - Updated to Vulkan 1.3.281.
+            - Updated to SDL 2.30.1.
+            - Updated to latest OpenCL specifications.
+            - Updated to latest SPIR-V Reflect.
+            - Updated to latest WebGPU/Dawn/WGPU headers.
+            - Updated Vkd3d native binaries.
+            - Fixed string marshalling occasionally resulting in memory access violations on newer .NET 8 versions.
+            - Fixed Windowing crashing on .NET Framework builds with prefer 32-bit set using GLFW.
+            - Fixed extension loading generic type usage issues with full IL trimming enabled.
+            - Fixed erroneous BreakneckLock acquisition logic slowing input events on mobile/SDL. (thanks @ZingBallyhoo)
+            - Fixed windowing losing events when using multiple windows on desktop with the mobile/SDL implementation. (thanks @ZingBallyhoo)
+            - Fixed some packages not referencing their native counterparts where appropriate. (thanks @alexrp)
+            - Fixed Input events for standalone joysticks not being tracked on GLFW.
+            - Fixed Input events no longer being tracked after 3-10 reopens of the same window on GLFW.
+            - Fixed V-Sync configuration not persisting over window state changes in Windowing.
+            - Fixed Circle.Contains erroneously comparing the squared vector distance from its center against its non-squared radius. (thanks @djoyahoy)
+
+            After this update:
+            - Apple Silicon support is complete except for missing ANGLE binaries.
+            - Arm Linux support is complete except for missing DXVK, ANGLE, and Vulkan Loader (missing on 32-bit only) binaries.
+            - 64-bit Windows on Arm support is complete except for missing DXVK and ANGLE binaries.
+            - 32-bit Windows on Arm remains unsupported except for DirectStorage.
         </PackageReleaseNotes>
         <PackageTags Condition="'$(PackageTags)' == ''">OpenCL;OpenGL;OpenAL;OpenGLES;GLES;Vulkan;Assimp;DirectX;GLFW;SDL;Windowing;Input;Gamepad;Joystick;Keyboard;Mouse;SilkTouch;Source;Generator;C#;F#;.NET;DotNet;Mono;Vector;Math;Maths;Numerics;Game;Graphics;Compute;Audio;Sound;Engine;Silk;Silk.NET;Slim.NET;ElgarTK;GPU;Sharp;Science;Scientific;Visualization;Visual;Audiovisual;Windows;macOS;Linux;Android;Bindings;OSX;Wrapper;Native</PackageTags>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
         <PackageOutputPath>$(MSBuildThisFileDirectory)/../output_packages</PackageOutputPath>
         <RepositoryUrl>https://github.com/dotnet/Silk.NET</RepositoryUrl>
         <RepositoryType>Git</RepositoryType>
-        <VersionPrefix>2.20.0</VersionPrefix>
+        <VersionPrefix>2.21.0</VersionPrefix>
         <VersionSuffix Condition="'$(VersionSuffix)' == ''"></VersionSuffix>
         <Description Condition="'$(Description)' == ''">
             Silk.NET is a high-speed, advanced library, providing bindings to popular low-level APIs such as OpenGL, OpenCL, OpenAL, OpenXR, GLFW, SDL, Vulkan, Assimp, and DirectX.

generator.json

@@ -77,6 +77,44 @@
                     "glPointSizePointerOES"
                 ]
             },
+            "glIntAsPtr": {
+                "EdgeFlagPointer": ["pointer"],
+                "EdgeFlagPointerEXT": ["pointer"],
+                "EdgeFlagPointerListIBM": ["pointer"],
+                "VertexPointer": ["pointer"],
+                "VertexPointerEXT": ["pointer"],
+                "VertexPointerListIBM": ["pointer"],
+                "VertexPointervINTEL": ["pointer"],
+                "ColorPointer": ["pointer"],
+                "ColorPointerEXT": ["pointer"],
+                "ColorPointerListIBM": ["pointer"],
+                "ColorPointervINTEL": ["pointer"],
+                "IndexPointer": ["pointer"],
+                "IndexPointerEXT": ["pointer"],
+                "IndexPointerListIBM": ["pointer"],
+                "NormalPointer": ["pointer"],
+                "NormalPointerEXT": ["pointer"],
+                "NormalPointerListIBM": ["pointer"],
+                "NormalPointervINTEL": ["pointer"],
+                "TexCoordPointer": ["pointer"],
+                "TexCoordPointerEXT": ["pointer"],
+                "TexCoordPointerListIBM": ["pointer"],
+                "TexCoordPointervINTEL": ["pointer"],
+                "MultiTexCoordPointerEXT": ["pointer"],
+                "FogCoordPointer": ["pointer"],
+                "FogCoordPointerEXT": ["pointer"],
+                "FogCoordPointerListIBM": ["pointer"],
+                "SecondaryColorPointer": ["pointer"],
+                "SecondaryColorPointerEXT": ["pointer"],
+                "SecondaryColorPointerListIBM": ["pointer"],
+                "VertexAttribPointer": ["pointer"],
+                "VertexAttribPointerARB": ["pointer"],
+                "VertexAttribPointerNV": ["pointer"],
+                "VertexAttribIPointer": ["pointer"],
+                "VertexAttribIPointerEXT": ["pointer"],
+                "TangentPointerEXT": ["pointer"],
+                "BinormalPointerEXT": ["pointer"]
+            },
             "extensionsNamespace": "Silk.NET.OpenGL.Extensions",
             "typeMaps": [
                 {
@@ -124,6 +162,44 @@
                 "Boolean"
             ],
             "namespace": "Silk.NET.OpenGL.Legacy",
+            "glIntAsPtr": {
+                "EdgeFlagPointer": ["pointer"],
+                "EdgeFlagPointerEXT": ["pointer"],
+                "EdgeFlagPointerListIBM": ["pointer"],
+                "VertexPointer": ["pointer"],
+                "VertexPointerEXT": ["pointer"],
+                "VertexPointerListIBM": ["pointer"],
+                "VertexPointervINTEL": ["pointer"],
+                "ColorPointer": ["pointer"],
+                "ColorPointerEXT": ["pointer"],
+                "ColorPointerListIBM": ["pointer"],
+                "ColorPointervINTEL": ["pointer"],
+                "IndexPointer": ["pointer"],
+                "IndexPointerEXT": ["pointer"],
+                "IndexPointerListIBM": ["pointer"],
+                "NormalPointer": ["pointer"],
+                "NormalPointerEXT": ["pointer"],
+                "NormalPointerListIBM": ["pointer"],
+                "NormalPointervINTEL": ["pointer"],
+                "TexCoordPointer": ["pointer"],
+                "TexCoordPointerEXT": ["pointer"],
+                "TexCoordPointerListIBM": ["pointer"],
+                "TexCoordPointervINTEL": ["pointer"],
+                "MultiTexCoordPointerEXT": ["pointer"],
+                "FogCoordPointer": ["pointer"],
+                "FogCoordPointerEXT": ["pointer"],
+                "FogCoordPointerListIBM": ["pointer"],
+                "SecondaryColorPointer": ["pointer"],
+                "SecondaryColorPointerEXT": ["pointer"],
+                "SecondaryColorPointerListIBM": ["pointer"],
+                "VertexAttribPointer": ["pointer"],
+                "VertexAttribPointerARB": ["pointer"],
+                "VertexAttribPointerNV": ["pointer"],
+                "VertexAttribIPointer": ["pointer"],
+                "VertexAttribIPointerEXT": ["pointer"],
+                "TangentPointerEXT": ["pointer"],
+                "BinormalPointerEXT": ["pointer"]
+            },
             "extensionsNamespace": "Silk.NET.OpenGL.Legacy.Extensions",
             "overloadExclusions": {
                 "RefOverloader": [
@@ -212,6 +288,44 @@
                 "Boolean"
             ],
             "namespace": "Silk.NET.OpenGLES",
+            "glIntAsPtr": {
+                "EdgeFlagPointer": ["pointer"],
+                "EdgeFlagPointerEXT": ["pointer"],
+                "EdgeFlagPointerListIBM": ["pointer"],
+                "VertexPointer": ["pointer"],
+                "VertexPointerEXT": ["pointer"],
+                "VertexPointerListIBM": ["pointer"],
+                "VertexPointervINTEL": ["pointer"],
+                "ColorPointer": ["pointer"],
+                "ColorPointerEXT": ["pointer"],
+                "ColorPointerListIBM": ["pointer"],
+                "ColorPointervINTEL": ["pointer"],
+                "IndexPointer": ["pointer"],
+                "IndexPointerEXT": ["pointer"],
+                "IndexPointerListIBM": ["pointer"],
+                "NormalPointer": ["pointer"],
+                "NormalPointerEXT": ["pointer"],
+                "NormalPointerListIBM": ["pointer"],
+                "NormalPointervINTEL": ["pointer"],
+                "TexCoordPointer": ["pointer"],
+                "TexCoordPointerEXT": ["pointer"],
+                "TexCoordPointerListIBM": ["pointer"],
+                "TexCoordPointervINTEL": ["pointer"],
+                "MultiTexCoordPointerEXT": ["pointer"],
+                "FogCoordPointer": ["pointer"],
+                "FogCoordPointerEXT": ["pointer"],
+                "FogCoordPointerListIBM": ["pointer"],
+                "SecondaryColorPointer": ["pointer"],
+                "SecondaryColorPointerEXT": ["pointer"],
+                "SecondaryColorPointerListIBM": ["pointer"],
+                "VertexAttribPointer": ["pointer"],
+                "VertexAttribPointerARB": ["pointer"],
+                "VertexAttribPointerNV": ["pointer"],
+                "VertexAttribIPointer": ["pointer"],
+                "VertexAttribIPointerEXT": ["pointer"],
+                "TangentPointerEXT": ["pointer"],
+                "BinormalPointerEXT": ["pointer"]
+            },
             "extensionsNamespace": "Silk.NET.OpenGLES.Extensions",
             "overloadExclusions": {
                 "RefOverloader": [
@@ -763,6 +877,9 @@
             "typeMaps": [
                 {
                     "$typemapPrecedesInjections": "true",
+                    "XrFutureEXT": "FutureEXT",
+                    "PFN_xrGetInstanceProcAddr": "PfnGetInstanceProcAddr",
+                    "PFN_xrCreateApiLayerInstance": "PfnCreateApiLayerInstance",
                     "char": "byte",
                     "XR_DEFINE_ATOM": "uint64_t",
                     "LUID": "ulong",

src/Core/Silk.NET.BuildTools/Bind/ClassWriter.cs

@@ -276,10 +276,7 @@ static string GetSignature(Function func)
                         sw.WriteLine("        public bool TryGetExtension<T>(out T ext)");
                         sw.WriteLine($"            where T:NativeExtension<{@class.ClassName}>");
                         sw.WriteLine("        {");
-                        sw.WriteLine("             ext = IsExtensionPresent(GetExtensionAttribute(typeof(T)).Name)");
-                        sw.WriteLine("                 ? (T) Activator.CreateInstance(typeof(T), Context)");
-                        sw.WriteLine("                 : null;");
-                        sw.WriteLine("             return ext is not null;");
+                        sw.WriteLine("             throw new NotImplementedException();");
                         sw.WriteLine("        }");
                         sw.WriteLine();
                         sw.WriteLine("        public override bool IsExtensionPresent(string extension)");

src/Core/Silk.NET.BuildTools/Common/Builders/TypeSignatureBuilder.cs

@@ -37,6 +37,8 @@ public sealed class TypeSignatureBuilder
         private Function _newFunctionPointerSignature;
 
         private List<Type> _newGenericParams;
+
+        private bool _newIsIntAsPtr;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="TypeSignatureBuilder" /> class.
@@ -56,6 +58,7 @@ public TypeSignatureBuilder(Type typeSignature)
             _newIsGenericType = typeSignature.IsGenericTypeParameterReference;
             _newFunctionPointerSignature = typeSignature.FunctionPointerSignature;
             _newGenericParams = typeSignature.GenericTypes;
+            _newIsIntAsPtr = typeSignature.IsIntAsPtr;
         }
 
         /// <summary>
@@ -142,7 +145,8 @@ public Type Build()
                 OriginalGroup = _newOriginalGroup,
                 OriginalClass = _newOriginalClass,
                 IsGenericTypeParameterReference = _newIsGenericType,
-                GenericTypes = _newGenericParams
+                GenericTypes = _newGenericParams,
+                IsIntAsPtr = _newIsIntAsPtr
             };
         }
 
@@ -191,6 +195,12 @@ public TypeSignatureBuilder WithGenericTypes(params Type[] parameters)
             _newGenericParams = parameters.ToList();
             return this;
         }
+
+        public TypeSignatureBuilder WithIsIntAsPtr(bool isIntAsPtr)
+        {
+            _newIsIntAsPtr = isIntAsPtr;
+            return this;
+        }
         // ReSharper restore UnusedParameter.Global
     }
 }

src/Core/Silk.NET.BuildTools/Common/Functions/Type.cs

@@ -102,6 +102,12 @@ public int IndirectionLevels
         /// </summary>
         public bool IsThis { get; set; }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether this is a pointer that is actually an integer and not a pointer to a
+        /// memory location.
+        /// </summary>
+        public bool IsIntAsPtr { get; set; }
+
         /// <summary>
         /// Gets or sets the function pointer signature if this type is a function pointer. May be null.
         /// </summary>