Answer: 
Above figure shows the overall architecture of WPF. It has three major sections presentation core, presentation framework and milcore. In the same diagram we have shown how other section like direct and operating system interact with the system. So let’s go section by section to understand how every section works.
User32:- It decides which goes where on the screen.
DirectX: - As said previously WPF uses directX internally. DirectX talks with drivers and renders the content.
Milcore: - Mil stands for media integration library. This section is a unmanaged code because it acts like a bridge between WPF managed and DirectX / User32 unmanaged API.
Presentation core ;- This is a low level API exposed by WPF providing features for 2D , 3D , geometry etc.
Presentation framework:- This section has high level features like application controls , layouts . Content etc which helps you to build up your application.