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Experimental Features

When Developer Extras are enabled in the Interface tab, a new Preferences experimental tab is shown. It contains non-production ready features that need feedback and design iterations.

Rule of Thumb

Any experimental features should not change how a file renders, regardless of the user preference. These preferences are only to be used to show or hide features in the user interface, and not to disable functionality.

DNA Changes and Check

The DNA struct UserDef_Experimental contains the variables that enable/disable experimental features in the user interface:

typedef struct UserDef_Experimental {
  char use_tool_fallback;
  char virtual_reality;
  char _pad0[6];
} UserDef_Experimental;

Although this is not the most efficient way of handling multiple variables, it is very easy to remove a setting when it is no longer experimental.

Use the macro USER_EXPERIMENTAL_TEST to test whether the features are enabled.

RNA Changes

In the file you need to create a new property in rna_def_userdef_experimental, but its get function can be auto-generated with the macro RNA_USERDEF_EXPERIMENTAL_BOOLEAN_GET:



static void rna_def_userdef_experimental(BlenderRNA *brna)
  StructRNA *srna;
  PropertyRNA *prop;

  srna = RNA_def_struct(brna, "PreferencesExperimental", NULL);
  RNA_def_struct_sdna(srna, "UserDef_Experimental");
  RNA_def_struct_nested(brna, srna, "Preferences");
  RNA_def_struct_clear_flag(srna, STRUCT_UNDO);
  RNA_def_struct_ui_text(srna, "Experimental", "Experimental features");


  prop = RNA_def_property(srna, "use_tool_fallback", PROP_BOOLEAN, PROP_NONE);
  RNA_def_property_boolean_sdna(prop, NULL, "use_tool_fallback", 1);
  RNA_def_property_boolean_funcs(prop, "rna_userdef_experimental_use_tool_fallback_get", NULL);
  RNA_def_property_ui_text(prop, "Fallback Tool Support", "Allow selection with an active tool");
  RNA_def_property_update(prop, 0, "rna_userdef_update");


Sometimes we have an operator which is experimental, so it will not be in the user interface at all times. However its poll() function should not be affected by the experimental value.

This way we can make sure anyone building an add-on that calls this operator will have predictable results regardless of the user preferences. The downside is that this operator will be visible in the Operator Search.