I frequently see screen size and desktop size in graphics programming forum or some documents, Isn’t screen size equal to desktop size? take the following as an example, what’s the differences?
For windowed mode, the size of the destination surface should be the
size of the desktop. For full-screen mode, the size of the destination
surface should be the screen size.
That is because the Desktop Size does NOT always fill the screen. Change your resolution to maybe 800×600 or (if possible) 640×480, and you will see that on many screens, it will only occupy a small area on the display. Screen size = the full amount your screen can show. Desktop size is that box that I just described. MOST cases, they are the same – but not always.
It also, depending on the context, may be describing what fits inside the current window, minus the title bar, tool bars, task bar, etc.