Hall of Mirrors

The Hall of Mirrors effect is a rendering glitch present in many games, including Halo 3. The glitch occurs when nothing is rendered to a particular region of the screen. This glitch can be recreated in the Unity game engine by turning off the "Clear flags" effect, then entering play mode.

Description
When a video game, such as Halo 3, renders a 3D animation, it does so by generating frames of animation. Once the frame of animation has been created, it is then displayed on the screen—specifically, it is drawn over the previous frame, covering it.

Sometimes, however, when a frame of 3D animation is rendered, nothing—not even a skybox—is rendered to a particular region of the screen. This results in parts of the affected frame being transparent. When the new frame is then drawn over the previous frame, parts of the previous frame show through. In nearly all games, this can result in a "hall of mirrors" or "afterimage" effect; if, in Halo 3, it occurs on Player 2's screen during split-screen gameplay, then parts of Player 1's screen will appear on Player 2's screen.

When playing a Campaign or Multiplayer level, if a player can see outside the level—that is, if they can see the void surrounding the level—then they will see the hall of mirrors effect. However, when saving a screenshot or showing a Campaign film, the effect is replaced with a solid color (usually sky blue in Multiplayer or off-white in Campaign). Furthermore, after taking a screenshot, the hall of mirrors effect sometimes shows part of the game's GUI (e.x. parts of the keyboard dialog box that is used to type a screenshot's name and description).

Explanation
To be more specific, the frames of animation are created by the rendering engine and stored in a framebuffer. The framebuffer is basically a storage area for frame data. When a frame is displayed, it is sent to the framebuffer.

The hall of mirrors effect results from the fact that the framebuffer is not cleared between frames. That is, the data from the previous frame is not deleted from the framebuffer before the next frame is drawn, so if the next frame has transparent regions, then the undeleted data from the previous frame will show through.

There is also an explanation for the phenomenon that occurs when the hall of mirrors effect is seen during split-screen gameplay. If the same framebuffer was used for each of the split screens, then Player 1's screen would show through any transparent areas on Player 2's screen, because Player 2's screen is effectively drawn over Player 1's.

Seeing the Hall of Mirrors Effect
There are a variety of ways to view the effect. Any time a player gets outside the map or sees a gap in the level geometry, they may see the effect.

If Pan Cam is used to get outside a level's boundaries, then the hall of mirrors glitch is almost guaranteed to appear.

The Storm
Start The Storm at Rally Point Alpha on Co-op. During the part that the Scarab Tanks appear, two players must be on a Mongoose, and drive them against a door and the passenger to alight. If done correctly, the game will freeze for 10 seconds. The Scarab will disappear, and if you go to the door, you will see the hall of mirrors effect.

The Covenant
At the beginning of The Covenant, after taking out the (normal) Wraith, if you climb up the surface of the tower you are supposed to enter, you will find a rift in the snow that shows the hall of mirrors effect.

Another hall of mirrors effect occurs in this level. Start the level at Rally Point Alpha. Get into a Hornet and fly to the second tower. Look directly at it and hover down to the left. You will be facing a ledge; fly towards it. Park the Hornet onto the longest ledge, and face the rock wall. Turn left and move forward to a crack in the rock. When you look into it, you will see the hall of mirrors effect.

The glitch can also be seen when the Time travel glitch is performed.

Halo
Start Halo at Rally Point Alpha on Co-op, right after you kill 343 Guilty Spark. One player should move forwards and kill the Flood forces ahead; the other one should remain where they spawned. The stationary player should turn and look behind them. They will see two doors; they need to go to the bottom of the one on the left, and look straight up. There will be a small crack that displays the hall of mirrors effect.

Isolation
On the default Isolation, go up to the Forerunner Wall, and try to force a teleporter through it. Once it's out, go through it, and you should see a Hall of Mirrors Effect.

Sandtrap
The glitch can be done in Sandtrap in Forge. Go into Edit Mode, and fly into the chasm-like structure and face the high dunes that cover up the barrier. Look right, and move forward into the indention of the top of the wall just below the ledge and zoom in. You should see the hall of mirrors effect there.

Prepare to Drop
The "Hall of Mirrors" glitch can be done by observing the untextured exterior of the UNSC Say My Name ship in the level Prepare to Drop in Theater mode.