82: Design Patterns: Double Buffer.

What is the double buffer design pattern? The double buffer behavioral pattern allows multiple changes to all appear to occur at the same time. Use it when you need readers to have access to current information while writers are updating a new version. Once everything is ready, then the new version becomes the current and the old current version is recycled to become the next new version. This design pattern also starts a new series of design patterns focused more on game development. This pattern can be found in the book “Game Programming Patterns” by Robert Nystrom. I recommend this book in addition to listening to my audio explanation because the author has an explanation that’s designed for the written page. The most common application of this pattern in game programming is probably the screen updates. It takes a while to draw each frame as it needs to appear. And this process usually starts with a blank canvas and gets built up bit by bit. Some parts can even get updated multiple times as some image is drawn and then overwritten by some other image. Only once the frame is completely drawn should it be sent to the screen. During the time the new frame is being drawn, it’s possible that the video card will need to be refreshing the screen on its own schedule. By updating a separate buffer, your application can let the video card use the current frame until the new one is ready. This pattern can help not just with video refreshes. You can also manage class property values in the same way. If you have an object with lots of properties and you want to update some of them but the update really needs to be done all at once in order to make any sense, then this pattern can help. You’ll need to keep two copies of the data in memory with some way to switch between them. The easiest way to switch is to maintain two pointers, a current pointer and a next pointer. And you can also use this pattern for cancelling updates. Let’s say you have a dialog box where the user can enter different values in data fields. The dialog box will have an Ok and a Cancel button. While changes are being made, put the new values in the next buffer. If the user commits the changes, then swap the buffers. And if the user cancels, then you don’t need to worry about restoring anything because you left all the original data unchanged. The Cancel button just causes the second buffer to be discarded. Or you can just clear it and be ready for another possible update. If you’d like to read the book that describes this pattern along with diagrams and sample code, then you can find Game Programming Patterns at the Resources page. You can find all my favorite books and resources at this page to help you create better software designs. Listen to the full episode about this design pattern or you can also read the full transcript below. Transcript The basic description says that this pattern causes multiple operations done sequentially to appear to be done at the same time. We’ve actually finished going through all the patterns in the Gang of Four book and I’m now explaining various patterns from other books. There’s a really good book called Game Programming Patterns by Robert Nystrom that I recommend that documents several more patterns applicable to game development. All of these patterns from the Gang of Four to any more recent book about design patterns describe well known and common practices. There’s nothing new or unique about a pattern because if so, then it wouldn’t be a pattern. Even though I’m explaining the patterns, I recommend that you buy a copy of the books I mention because the authors explain the patterns in a way that best fits a written page. The authors can also use diagrams. Anytime you can learn through multiple techniques, you’ll learn better and faster. So make sure to get the books in addition to listening to this podcast. In the book Game Programming Pa