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Once you have imported a model and while editing it, you will see exactly how it will look once added to the game, thanks to the addon's automatic generation of materials for blizzlike rendering. Here is a comparison of the same WMO imported with the addon (left) and as an .obj via WMV (right): The addon supports both the internal Blender renderer (soon to become Eevee renderer) and Cycles renderer, with materials generated for the one you import the model in. You can change the renderer and re-generate materials at any time. The addon provides you with a vast array of tools to show, hide, and edit any aspect of the WMO. You can change the existing mesh, create new rooms with portals between them, move doodads around, and light everything up! In addition to manual editing, many tasks can be auto-performed globally, for example ambient lighting: Doodads, too, can be lightmapped manually or auto-aligned to fit the surroundings:
The addon allows you to import any M2 or WMO without conversion: either an extracted one from somewhere on your computer or directly from WoW Model Viewer. In both cases, the addon will do its best to find the required textures, doodads, etc. and import them automatically, unless you tell it otherwise.