Merge pull request AvaloniaUI#3363 from PJB3005/19-12-16-egl

Fix loading EGL functions on GLX.

Author: danwalmsley

src/Avalonia.X11/Glx/Glx.cs

@@ -84,8 +84,24 @@ public delegate IntPtr GlxCreateContextAttribsARB(IntPtr dpy, IntPtr fbconfig, I
         [GlEntryPoint("glGetError")]
         public GlGetError GetError { get; }
 
-        public GlxInterface() : base(GlxGetProcAddress)
+        public GlxInterface() : base(SafeGetProcAddress)
         {
         }
+
+        // Ignores egl functions.
+        // On some Linux systems, glXGetProcAddress will return valid pointers for even EGL functions.
+        // This makes Skia try to load some data from EGL,
+        // which can then cause segmentation faults because they return garbage.
+        public static IntPtr SafeGetProcAddress(string proc, bool optional)
+        {
+            if (proc.StartsWith("egl", StringComparison.InvariantCulture))
+            {
+                return IntPtr.Zero;
+            }
+
+            return GlxConverted(proc, optional);
+        }
+
+        private static readonly Func<string, bool, IntPtr> GlxConverted = ConvertNative(GlxGetProcAddress);
     }
 }

src/Avalonia.X11/Glx/GlxDisplay.cs

@@ -87,7 +87,7 @@ public GlxDisplay(X11Info x11)
             ImmediateContext.MakeCurrent();
             var err = Glx.GetError();
 
-            GlInterface = new GlInterface(GlxInterface.GlxGetProcAddress);
+            GlInterface = new GlInterface(GlxInterface.SafeGetProcAddress);
             if (GlInterface.Version == null)
                 throw new OpenGlException("GL version string is null, aborting");
             if (GlInterface.Renderer == null)