dxsdk当中是有说明的
IDirect3D9::GetDeviceCaps Method
The application should not assume the persistence of vertex processing capabilities across Direct3D device objects. The particular capabilities that a physical device exposes may depend on parameters supplied to CreateDevice. For example, the capabilities may yield different vertex processing capabilities before and after creating a Direct3D Device Object with hardware vertex processing enabled.
IDirect3DDevice创建时候的参数不同,使得返回的能力数值也会不同的
你更应该依赖于IDirect3DDevice的返回数值