Added support for creating GL context using the "assemble" methods

binding/Binding/GRGlInterface.cs

@@ -8,11 +8,27 @@
 //
 
 using System;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
 
 namespace SkiaSharp
 {
+	// public delegates
+	public delegate IntPtr GRGlGetProcDelegate (object context, string name);
+
+	// internal proxy delegates
+	[UnmanagedFunctionPointer (CallingConvention.Cdecl)]
+	internal delegate IntPtr GRGlGetProcDelegateInternal (IntPtr context, string name);
+
 	public class GRGlInterface : SKObject
 	{
+		// so the GC doesn't collect the delegate
+		private static readonly GRGlGetProcDelegateInternal getProcDelegate;
+		static GRGlInterface ()
+		{
+			getProcDelegate = new GRGlGetProcDelegateInternal (GrGLGetProcInternal);
+		}
+
 		[Preserve]
 		internal GRGlInterface (IntPtr h, bool owns)
 			: base (h, owns)
@@ -29,6 +45,54 @@ namespace SkiaSharp
 			return GetObject<GRGlInterface> (SkiaApi.gr_glinterface_create_native_interface ());
 		}
 
+		public static GRGlInterface AssembleInterface (GRGlGetProcDelegate get)
+		{
+			return AssembleInterface (null, get);
+		}
+
+		public static GRGlInterface AssembleInterface (object context, GRGlGetProcDelegate get)
+		{
+			var del = Marshal.GetFunctionPointerForDelegate (getProcDelegate);
+
+			var ctx = new GRGlGetProcDelegateContext (context, get);
+			var ptr = ctx.Wrap ();
+			var glInterface = GetObject<GRGlInterface> (SkiaApi.gr_glinterface_assemble_interface (ptr, del));
+			GRGlGetProcDelegateContext.Free (ptr);
+			return glInterface;
+		}
+
+		public static GRGlInterface AssembleGlInterface (GRGlGetProcDelegate get)
+		{
+			return AssembleGlInterface (null, get);
+		}
+
+		public static GRGlInterface AssembleGlInterface (object context, GRGlGetProcDelegate get)
+		{
+			var del = Marshal.GetFunctionPointerForDelegate (getProcDelegate);
+
+			var ctx = new GRGlGetProcDelegateContext (context, get);
+			var ptr = ctx.Wrap ();
+			var glInterface = GetObject<GRGlInterface> (SkiaApi.gr_glinterface_assemble_gl_interface (ptr, del));
+			GRGlGetProcDelegateContext.Free (ptr);
+			return glInterface;
+		}
+
+		public static GRGlInterface AssembleGlesInterface (GRGlGetProcDelegate get)
+		{
+			return AssembleGlesInterface (null, get);
+		}
+
+		public static GRGlInterface AssembleGlesInterface (object context, GRGlGetProcDelegate get)
+		{
+			var del = Marshal.GetFunctionPointerForDelegate (getProcDelegate);
+
+			var ctx = new GRGlGetProcDelegateContext (context, get);
+			var ptr = ctx.Wrap ();
+			var glInterface = GetObject<GRGlInterface> (SkiaApi.gr_glinterface_assemble_gles_interface (ptr, del));
+			GRGlGetProcDelegateContext.Free (ptr);
+			return glInterface;
+		}
+
 		public GRGlInterface Clone ()
 		{
 			return GetObject<GRGlInterface> (SkiaApi.gr_glinterface_clone (Handle));
@@ -52,6 +116,54 @@ namespace SkiaSharp
 
 			base.Dispose (disposing);
 		}
+
+		// internal proxy
+		#if __IOS__
+		[ObjCRuntime.MonoPInvokeCallback (typeof (GRGlGetProcDelegateInternal))]
+		#endif
+		private static IntPtr GrGLGetProcInternal (IntPtr context, string name)
+		{
+			var ctx = GRGlGetProcDelegateContext.Unwrap (context);
+			return ctx.GetProc (ctx.Context, name);
+		}
+
+		// This is the actual context passed to native code.
+		// Instead of marshalling the user's data as an IntPtr and requiring 
+		// him to wrap/unwarp, we do it via a proxy class. This also prevents 
+		// us from having to marshal the user's callback too. 
+		private struct GRGlGetProcDelegateContext
+		{
+			// the "managed version" of the callback 
+			public readonly GRGlGetProcDelegate GetProc;
+			public readonly object Context;
+
+			public GRGlGetProcDelegateContext (object context, GRGlGetProcDelegate get)
+			{
+				Context = context;
+				GetProc = get;
+			}
+
+			// wrap this context into a "native" pointer
+			public IntPtr Wrap ()
+			{
+				var gc = GCHandle.Alloc (this, GCHandleType.Pinned);
+				return GCHandle.ToIntPtr (gc);
+			}
+
+			// unwrap the "native" pointer into a managed context
+			public static GRGlGetProcDelegateContext Unwrap (IntPtr ptr)
+			{
+				var gchandle = GCHandle.FromIntPtr (ptr);
+				return (GRGlGetProcDelegateContext) gchandle.Target;
+			}
+
+			// unwrap and free the context
+			public static void Free (IntPtr ptr)
+			{
+				var gchandle = GCHandle.FromIntPtr (ptr);
+				gchandle.Free ();
+			}
+		}
 	}
 }
 

binding/Binding/SkiaApi.cs

@@ -1056,6 +1056,12 @@ namespace SkiaSharp
 		
 		// GLInterface
 		
+		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
+		public extern static gr_glinterface_t gr_glinterface_assemble_interface (IntPtr ctx, IntPtr get);
+		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
+		public extern static gr_glinterface_t gr_glinterface_assemble_gl_interface (IntPtr ctx, IntPtr get);
+		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
+		public extern static gr_glinterface_t gr_glinterface_assemble_gles_interface (IntPtr ctx, IntPtr get);
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
 		public extern static gr_glinterface_t gr_glinterface_default_interface ();
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]

skia

@@ -1 +1 @@
-Subproject commit 18f95a7963dd1eac6ef8b4cdab94c92f8ca9b63b
+Subproject commit 065c1e637d3bc0e3766ab286cf2f0335f019616b