How to Build a Prince-Of-Persia-Style Time-Rewind System, Part 1

What You'll Be Creating

In this tutorial, we'll build a simple game where the player can rewind progress in Unity (it can also be adapted to work in other systems). This first part will go into the basics of the system, and the next part will flesh it out and make it much more versatile.

First, though we'll take a look at what games use this. Then we'll look at the other uses for this technical setup, before ultimately creating a small game that we can rewind, which should give you a basis for your own.

A demonstation of the basic functionality

You will need the newest version of Unity for this, and should have some experience with it. The source code is also available for download if you want to check your own progress against it.

Ready? Let's go!

How Has This Been Used Before?

Prince of Persia: The Sands of Time is one of the first games to truly integrate a time-rewinding mechanic into its gameplay. When you die you do not just have to reload, but can rather rewind the game for a few seconds to where you were alive again, and immediately try again.

Prince of Persia: The Forgotten Sands. The Sands Of Time Trilogy integrates time-rewinding beautifully into its gameplay and avoids immersion-breaking quick-reloading.

This mechanic is not only integrated into the gameplay, but the narrative and universe as well, and is mentioned throughout the story.

Other games that employ these systems are Braid, for example, which is also centered around the winding of time. The hero Tracer in Overwatch has a power that resets her to a position a few seconds ago, essentially rewinding her time, even in a multiplayer game. The GRID-series of racing games also has a snapshot-mechanic, where you have a small pool of rewinds during a race, which you can access when you have a critical crash. This prevents frustration caused by crashes near the end of race, which can be especially infuriating.

When you have a fatal crash in GRID you get the chance to rewind the game to a point before the crash.

Other Uses

But this system can not only be used to replace quick-saving. Another way this is employed is ghosting in racing games and asynchronous multiplayer.

Replays
Replays are another fun way to employ this feature. This can be seen in games like SUPERHOT, the Worms series, and pretty much the majority of sports games.

Sports-replays work the same way they are presented on TV, where an action is showed again, possibly from a different angle. For this not a video is recorded but rather the actions of the user, allowing the replay to employ different camera angles and shots. The Worms games use this in a humorous way, where very comical or effective kills are shown in an Instant Replay.

SUPERHOT also records your movement. When you are done playing around your entire progress is then replayed, showing the few seconds of actual movement that happened.

Super Meat Boy uses this in a fun way. When you finish a level you see a replay of all your previous attempts laid on top of each other, culminating with your finishing run being the last left standing.

The end-of-level replay in Super Meat Boy. Every one of your previous attempts is recorded and then played back at the same time.

Time-Trial Ghosts
Race-Ghosting is a technique where you race for the best time on an empty track. But at the same time, you race against a ghost, which is a ghostly, transparent car, which drives the exact way you raced before on your best attempt. You cannot collide with it, which means you can still concentrate on getting the best time.

Instead of driving alone you get to compete against yourself, which makes time-trials much more fun. This feature shows up in the majority of racing games, from the Need for Speed series to Diddy Kong Racing.

Racing a ghost in Trackmania Nations. This one has the silver difficulty, meaning I will get the silver medal if I beat them. Note the overlap in car-models, showing the ghost isn't corporeal and can be driven through.

Multiplayer-Ghosts
Asynchronous Multiplayer-Ghosting is another way to use this setup. In this rarely-used feature, multiplayer matches are accomplished by recording the data of one player, who then sends their run to another player, who can subsequently battle against the first player. The data is applied the same way a time-trial-ghost would be, only that you are racing against another player.

A form of this shows up in the Trackmania-games, where it is possible to race against certain difficulties. These recorded racers will give you an opponent to beat for a certain reward.

Movie-Editing
Few games offer this from the get-go but used right it can be a fun tool.Team Fortress 2 offers a built-in replay-editor, with which you can create your own clips.

The replay editor from Team Fortress 2. Once recorded a match can be seen from any perspective, not just the player's.

Once the feature has been activated you can record and watch previous matches. The vital element is that everything is recorded, not only your view. This means you can move around the recorded game-world, see where everyone is, and have control over time.
Written by Matthias Zarzecki (continue)

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