Texture2D.CreateExternalTexture
static function CreateExternalTexture(width: int, height: int, format: TextureFormat, mipmap: bool, linear: bool, nativeTex: IntPtr): Texture2D;
static Texture2D CreateExternalTexture(int width, int height, TextureFormat format, bool mipmap, bool linear, IntPtr nativeTex);
static def CreateExternalTexture(width as int, height as int, format as TextureFormat, mipmap as bool, linear as bool, nativeTex as IntPtr) as Texture2D
Parameters

nativeTex Native texture object.
Description

Creates Unity Texture on top of already inited native texture object.

You should make sure that params specified here are the same as the ones used for creation of native texture. Native texture object on Direct3D-like devices is a pointer to the base type, from which a texture can be created (IDirect3DBaseTexture9 on D3D9, ID3D11ShaderResourceView on D3D11). On OpenGL/OpenGL ES it is GLuint.