From 8a7ccd3019fa2ed27b0c2fa1e5dad33462e0202a Mon Sep 17 00:00:00 2001
From: Eric Mellino <mellinoe@gmail.com>
Date: Mon, 19 Mar 2018 19:55:07 -0700
Subject: [PATCH] [Metal] Add a real support check for Metal.

---
 src/Veldrid.MetalBindings/MTLDevice.cs |  3 +++
 src/Veldrid.MetalBindings/NSArray.cs   | 14 ++++++++++
 src/Veldrid/GraphicsDevice.cs          |  2 +-
 src/Veldrid/MTL/MTLGraphicsDevice.cs   | 36 ++++++++++++++++++++++++++
 4 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 src/Veldrid.MetalBindings/NSArray.cs

diff --git a/src/Veldrid.MetalBindings/MTLDevice.cs b/src/Veldrid.MetalBindings/MTLDevice.cs
index 39590cccc..716a6672c 100644
--- a/src/Veldrid.MetalBindings/MTLDevice.cs
+++ b/src/Veldrid.MetalBindings/MTLDevice.cs
@@ -126,6 +126,9 @@ public Bool8 isDepth24Stencil8PixelFormatSupported
         [DllImport(MetalFramework)]
         public static extern MTLDevice MTLCreateSystemDefaultDevice();
 
+        [DllImport(MetalFramework)]
+        public static extern NSArray MTLCopyAllDevices();
+
         private static readonly Selector sel_name = "name";
         private static readonly Selector sel_maxThreadsPerThreadgroup = "maxThreadsPerThreadgroup";
         private static readonly Selector sel_newLibraryWithSource = "newLibraryWithSource:options:error:";
diff --git a/src/Veldrid.MetalBindings/NSArray.cs b/src/Veldrid.MetalBindings/NSArray.cs
new file mode 100644
index 000000000..8395a6991
--- /dev/null
+++ b/src/Veldrid.MetalBindings/NSArray.cs
@@ -0,0 +1,14 @@
+using System;
+using static Veldrid.MetalBindings.ObjectiveCRuntime;
+
+namespace Veldrid.MetalBindings
+{
+    public struct NSArray
+    {
+        public readonly IntPtr NativePtr;
+        public NSArray(IntPtr ptr) => NativePtr = ptr;
+
+        public UIntPtr count => UIntPtr_objc_msgSend(NativePtr, sel_count);
+        private static readonly Selector sel_count = "count";
+    }
+}
\ No newline at end of file
diff --git a/src/Veldrid/GraphicsDevice.cs b/src/Veldrid/GraphicsDevice.cs
index 934f251a8..56d4e0053 100644
--- a/src/Veldrid/GraphicsDevice.cs
+++ b/src/Veldrid/GraphicsDevice.cs
@@ -595,7 +595,7 @@ public static bool IsBackendSupported(GraphicsBackend backend)
 #endif
                 case GraphicsBackend.Metal:
 #if !EXCLUDE_METAL_BACKEND
-                    return RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
+                    return MTL.MTLGraphicsDevice.IsSupported();
 #else
                     return false;
 #endif
diff --git a/src/Veldrid/MTL/MTLGraphicsDevice.cs b/src/Veldrid/MTL/MTLGraphicsDevice.cs
index dce6e5062..34fb3a1f0 100644
--- a/src/Veldrid/MTL/MTLGraphicsDevice.cs
+++ b/src/Veldrid/MTL/MTLGraphicsDevice.cs
@@ -11,6 +11,8 @@ namespace Veldrid.MTL
 {
     internal unsafe class MTLGraphicsDevice : GraphicsDevice
     {
+        private static readonly Lazy<bool> s_isSupported = new Lazy<bool>(GetIsSupported);
+
         private readonly MTLDevice _device;
         private readonly MTLCommandQueue _commandQueue;
         private readonly MTLSwapchain _mainSwapchain;
@@ -307,6 +309,40 @@ public override void ResetFence(Fence fence)
             Util.AssertSubtype<Fence, MTLFence>(fence).Reset();
         }
 
+        internal static bool IsSupported() => s_isSupported.Value;
+
+        private static bool GetIsSupported()
+        {
+            bool result = false;
+            try
+            {
+                if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+                {
+                    if (RuntimeInformation.OSDescription.Contains("Darwin"))
+                    {
+                        NSArray allDevices = MTLDevice.MTLCopyAllDevices();
+                        result |= (ulong)allDevices.count > 0;
+                        ObjectiveCRuntime.release(allDevices.NativePtr);
+                    }
+                    else
+                    {
+                        MTLDevice defaultDevice = MTLDevice.MTLCreateSystemDefaultDevice();
+                        if (defaultDevice.NativePtr != IntPtr.Zero)
+                        {
+                            result = true;
+                            ObjectiveCRuntime.release(defaultDevice.NativePtr);
+                        }
+                    }
+                }
+            }
+            catch
+            {
+                result = false;
+            }
+
+            return result;
+        }
+
         internal MTLComputePipelineState GetUnalignedBufferCopyPipeline()
         {
             lock (_unalignedBufferCopyPipelineLock)