Windows Xiaobai study notes

       1. InvalidRect invalidates the rectangular area and redraws this part;

　　2. After minimization, the length and width of hdc's rect will become 0;

　　3. Setting the animation is to give the object an initial speed;

　　4. The same object is needed to store the object, in order to prevent it from restarting movement when the window changes;

　　5. The first parameter in CreateWindow is the window class name, which must be the same as the one previously registered, otherwise the create will fail.