This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I thought only a character needs to be updated, not the background or any non-moving objects.
I thought about this after I removed the code that fills up the background in this program. The result was the image being shadowed, or the image the buffer replaced was never erased and left a trail of the image wherever the user dragged the mouse cursor.