First Thanks for the quick answer.
I want make possible to resize my window, but i want to keep the aspect ratio. So i added
case WM_SIZE:
case WM_SIZING:
in the WindowImplWin32.cpp, at first just for trying purposes, i think, so can i set the width to the new hight from my window. But when i resize the window, my game stop polling events from the stack, so i cant handle WM_SIZING-Events.