c_gdk_window_get_device_position_double

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
__gshared extern (C)
GdkWindow* function(GdkWindow* window, GdkDevice* device, double* x, double* y, GdkModifierType* mask) c_gdk_window_get_device_position_double;

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