add better support for using mesa when needed on windows

Add a header file function to handle some of the work in
testing opengl support and selecting mesa. Also add a cmake option
to turn on delayed loading for opengl.

(cherry picked from commit 29607014)

CMake/vtkOpenGL.cmake

@@ -146,6 +146,12 @@ if(VTK_CAN_DO_ONSCREEN)
   endif()
 endif()
 
+# windows  opengl delayed loading option
+if(WIN32)
+  option(VTK_USE_OPENGL_DELAYED_LOAD "Use delayed loading for the opengl dll" FALSE)
+  mark_as_advanced(VTK_USE_OPENGL_DELAYED_LOAD)
+endif()
+
 # Function to link a VTK target to the necessary OpenGL libraries.
 function(vtk_opengl_link target)
   if(VTK_OPENGL_HAS_OSMESA)
@@ -157,4 +163,8 @@ function(vtk_opengl_link target)
   if(VTK_CAN_DO_ONSCREEN)
     vtk_module_link_libraries(${target} LINK_PRIVATE ${OPENGL_LIBRARIES})
   endif()
+  if (VTK_USE_OPENGL_DELAYED_LOAD)
+    vtk_module_link_libraries(${target} LINK_PRIVATE delayimp.lib)
+    set_property(TARGET ${target} APPEND_STRING PROPERTY LINK_FLAGS "/DELAYLOAD:opengl32.dll")
+  endif()
 endfunction()

Rendering/OpenGL2/vtkTestOpenGLVersion.h

+/*=========================================================================
+
+  Program:   Visualization Toolkit
+
+  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
+  All rights reserved.
+  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notice for more information.
+
+=========================================================================*/
+/**
+ * This header file is designed to be included into your program
+ * to support delayed loading of opengl and if needed use of Mesa
+ * in cases where the users computer does not support OpenGL 3.2
+ * natively.
+ *
+ * To use this class you must
+ *
+ * 1) Build VTK with the advanced cmake option VTK_USE_OPENGL_DELAYED_LOAD
+ *    turned on.
+ *
+ * 2) Include this file in your application and call HandleOpenGL32Issues
+ *    before you do any rendering or anything that would cause opengl
+ *    to be used. Ideally do this right at the beginning of your program.
+ *
+ * 3) Make sure you include vtkTestOpenGLVersion.exe with your application
+ *    and pass the fullpath to it as the first argument to HandleOpenGL32Issues
+ *
+ * 4) Make sure you include the Mesa libraries with your application. Typically
+ *    this means opengl32.dll swrAVX.dll swrAVX2.dll and graw.dll. Pass the path
+ *    to these libraries as the second argument to HandleOpenGL32Issues
+ */
+
+#include <windows.h>
+
+// returns an int, zero indicates a problem though right now
+// all paths return 1.
+int HandleOpenGL32Issues(
+  const char *pathToTestOpenGLExecutable,
+  const char *mesaLibPath
+  )
+{
+  // run the test executable and collect the result
+  int result = system(pathToTestOpenGLExecutable);
+
+  // if the default works then just return
+  if (result == 0)
+  {
+    return 1;
+  }
+
+  // otherwise set the dll path so that mesa willbe loaded
+  SetDllDirectory(mesaLibPath);
+
+  return 1;
+}
+
+// VTK-HeaderTest-Exclude: vtkTestOpenGLVersion.h