OpenGL 4.0 fix

src/Avalonia.OpenGL/GlBasicInfoInterface.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Runtime.InteropServices;
 using Avalonia.Platform.Interop;
 
@@ -16,6 +18,7 @@ namespace Avalonia.OpenGL
         
         public delegate void GlGetIntegerv(int name, out int rv);
         public delegate IntPtr GlGetString(int v);
+        public delegate IntPtr GlGetStringi(int v, int v1);
     }
     
     public class GlBasicInfoInterface<TContextInfo> : GlInterfaceBase<TContextInfo>
@@ -34,6 +37,9 @@ namespace Avalonia.OpenGL
         
         [GlEntryPoint("glGetString")]
         public GlBasicInfoInterface.GlGetString GetStringNative { get; }
+        
+        [GlEntryPoint("glGetStringi")]
+        public GlBasicInfoInterface.GlGetStringi GetStringiNative { get; }
 
         public string GetString(int v)
         {
@@ -42,5 +48,25 @@ namespace Avalonia.OpenGL
                 return Marshal.PtrToStringAnsi(ptr);
             return null;
         }
+        
+        public string GetString(int v, int index)
+        {
+            var ptr = GetStringiNative(v, index);
+            if (ptr != IntPtr.Zero)
+                return Marshal.PtrToStringAnsi(ptr);
+            return null;
+        }
+
+        public List<string> GetExtensions()
+        {
+            var sp = GetString(GlConsts.GL_EXTENSIONS);
+            if (sp != null)
+                return sp.Split(' ').ToList();
+            GetIntegerv(GlConsts.GL_NUM_EXTENSIONS, out int count);
+            var rv = new List<string>(count);
+            for (var c = 0; c < count; c++)
+                rv.Add(GetString(GlConsts.GL_EXTENSIONS, c));
+            return rv;
+        }
     }
 }

src/Avalonia.OpenGL/GlInterface.cs

@@ -30,7 +30,7 @@ namespace Avalonia.OpenGL
             public static GlContextInfo Create(GlVersion version, Func<string, IntPtr> getProcAddress)
             {
                 var basicInfoInterface = new GlBasicInfoInterface(getProcAddress);
-                var exts = basicInfoInterface.GetString(GL_EXTENSIONS).Split(' ');
+                var exts = basicInfoInterface.GetExtensions();
                 return new GlContextInfo(version, new HashSet<string>(exts));
             }
         }

src/Avalonia.OpenGL/GlInterfaceBase.cs

@@ -48,6 +48,8 @@ namespace Avalonia.OpenGL
                         proc = typed.GetProcAddress(context, getProcAddress);
                     else if (attr is IGlEntryPointAttribute untyped)
                         proc = untyped.GetProcAddress(getProcAddress);
+                    if (proc != IntPtr.Zero)
+                        break;
                 }
                 
                 if (proc != IntPtr.Zero)