* [Context] check Visual before using it

diff --git a/uglcContextGtk2GLX.pas b/uglcContextGtk2GLX.pas
index b3ddb20..f9d1475 100644 (file)
--- a/uglcContextGtk2GLX.pas
+++ b/uglcContextGtk2GLX.pas
@@ -351,6 +351,9 @@ var
   attrList: TGLIntArray;\r
   drawable: PGdkDrawable;\r
 begin\r
+  if not Assigned(aControl) then\r
+    raise EArgumentException.Create('aControl is not assigned');\r
+\r
   {\r
     Temporary (realized) widget to get to display\r
   }\r
@@ -382,6 +385,8 @@ begin
       FVisual  := glXChooseVisual(FDisplay, DefaultScreen(FDisplay), @attrList[0]);\r
     end;\r
   end;\r
+  if not Assigned(FVisual) then\r
+    raise EGLXError.Create('choose visual failed');\r
 \r
   {\r
     Most widgets inherit the drawable of their parent. In contrast to Windows, descending from\r