first, create a button via CreateWindow(WC_BUTTON, ...)
second, draw a image via StretchDIBits(hdc, x, ...), the image memory is gotten with a camera
then, I want to draw the button created above on the image
I try to use ShowWindow, it will send a message to windows to draw the button
so ShowWindow and StretchDIBits maybe be draw button first, then draw image, or draw image first, then draw button
it's not what I want to do. I want to draw image first, then draw button immediately. Or the button is covered by the image.