So I recently upgraded to windows 10. Since upgrading, whenever I try to play DDC or LoLK full screen at 640x480 resolution, the gameplay screen only covers about a third of the actual screen (the rest is black). I'm also unable to use print screen to take a screenshot to show you what it looks like, but I roughly recreated in paint ;-;
Playing at higher 960x720 increases the size of the play screen, but doesn't actually make it full screen. It also causes significant lag because my computer sucks, so it's not really possible for me to play this way.
At first I assumed it was a problem with my computer, but someone else also described the same problem.