user32.dll and gdi32.dll

user32.dll提供了用户界面相互的API，例如CreateWindow, MessageBox等等，但是其底层是使用gdi32.dll中的函数来实现窗口界面的绘制,具体参考文章：User32.dll Lock the computer 虽然该文并不是讨论user32.dll和gdi32.dll的关系，但是其中有一句话：Many of the functions in user32.dll call GDI functions provided by gdi32.dll to make the rendering of the many of the elements of the user interface. Some programs are also calling the GDI functions directly to perform lower-level operations within a previously by user32 created window.

表明uer32.dll中的 API 调用gdi32.dll来实现UI元素的渲染

关于win32窗口的渲染：win32窗口渲染原理

窗口就是由像素点组成的

自己绘制窗口：draw Windows