vtkWheel: add feature flags for available rendering support

CMake/vtkWheelFinalization.cmake

@@ -15,5 +15,51 @@ if (TARGET VTK::RenderingOpenVR)
     "    'openvr': [],\n")
 endif ()
 
+if (TARGET VTK::RenderingOpenGL2)
+  set(has_onscreen OFF)
+  set(has_offscreen OFF)
+  if (VTK_USE_X)
+    string(APPEND vtk_feature_entries
+      "    'rendering-onscreen-x11': [],\n")
+    set(has_onscreen ON)
+  endif ()
+  if (VTK_USE_COCOA)
+    string(APPEND vtk_feature_entries
+      "    'rendering-onscreen-cocoa': [],\n")
+    set(has_onscreen ON)
+  endif ()
+  if (WIN32)
+    string(APPEND vtk_feature_entries
+      "    'rendering-onscreen-windows': [],\n")
+    set(has_onscreen ON)
+  endif ()
+  if (VTK_OPENGL_HAS_OSMESA)
+    string(APPEND vtk_feature_entries
+      "    'rendering-offscreen-osmesa': [],\n")
+    set(has_offscreen ON)
+  endif ()
+
+  if (has_onscreen)
+    string(APPEND vtk_feature_entries
+      "    'rendering-onscreen': [],\n")
+  endif ()
+  if (has_offscreen)
+    string(APPEND vtk_feature_entries
+      "    'rendering-offscreen': [],\n")
+  endif ()
+
+  if (VTK_OPENGL_USE_GLES)
+    string(APPEND vtk_feature_entries
+      "    'rendering-backend-gles': [],\n")
+  else ()
+    string(APPEND vtk_feature_entries
+      "    'rendering-backend-gl': [],\n")
+  endif ()
+  if (VTK_OPENGL_HAS_EGL)
+    string(APPEND vtk_feature_entries
+      "    'rendering-backend-egl': [],\n")
+  endif ()
+endif ()
+
 file(WRITE "${CMAKE_BINARY_DIR}/vtk_features.py"
   "FEATURES = {\n${vtk_feature_entries}}\n")