The Vireo class encapsulate the creation of the various objects needed by the graphics API such as the physical adapter and the logical device. The instance of the Vireo class is stored in the vireo field of the base Application class of your project. The creation of the instance is done in the os-specific main class (Win32Application for Windows) of your project after the user selects the runtime backend :

backend_select.png

The Vireo class is the main class of the library; You need an instance of this class to create all the library objects.

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Related manual page : The Vireo class