These ingenious optical illusions are hiding in some of our favourite games

We love a good optical illusion, and even more so when it serves a practical purpose to help achieve a design objective. Game developers use a wide range of clever techniques to trick players’ perceptions, making graphics richer, bigger, or more complex than they really are.

From parallax scrolling in classic 2D games to the repetition of textures to create the impression of complex surfaces, forced perspective to change how large objects look, and the use of fog and lighting to hide rendering limitations, illusions in game development can save processing power and development time while enhancing immersion.

Today these visual tricks are also a great way to promote a game. Many indie devs reveal the techniques they're using during the development process as part of their buildup to a game's release, helping to building engagement on social media.

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How I fake an infinite room in my puzzle game from r/IndieDev

In the post above on Reddit, CraftwareGG shares progress on a system developed for their upcoming fantasy puzzle adventure Realms of Riddles: Wizards' Keep. The solo developer created the illusion of an infinite room by using two hidden portals that constantly teleport the player between duplicated sections. The left side of the video shows what the player sees in the game, while the right side shows the scene view in Unity (see our guide to game development software).

Each portal has a plane and a camera, and the target portal's camera inversely replicates the player's movements. The plane renders what the target portal's camera sees through a shader. When the player crosses the plane, they're teleported to the target portal. Since it’s just another camera, the developer can choose whether the player gets rendered or not using layers and culling masks.

It's reminding some of the myhouse.wad modification for Doom II. The developer says they originally built the system for a different puzzle mechanic. The infinite room illusion came about naturally through experimentation. Tweaking of the portal settings and shadows and SSAO properties was necessary to achieve smooth lighting.

In the post above, game developer Maxime Minard, AKA Istrandar, reveals a trick used for their eerie upcoming roguelike cardbuilder Carnholt. The game's world looks to have a lot of depth to it, but when the camera is moved it's revealed to be mainly fixed points of view and projected textures. The owl even has two faces.

“Video games only need to look right from one angle!,” the developer points out.

“I start with painting the texture then I model around it from the camera POV,” they add. “My main goal is to have the geometry match the silouhette and grossly the shape. The camera won't move much and all lighting is baked in the texture so I don't need very complex mesh.”

As for why the back of the owl's head is textured, the developer is using camera projection so the UV map of the back of the head is placed in the same place as the front. “I could clean it up, but it's not really possible to notice it within the game,” they note.

In the post above, the Argentine developer and reverse engineering enthusiast Sammwy dissects Team Cherry's hugely popular Hollow Knight: Silksong using UnityExplorer to reveal that, like many 2D games, the metroidvania is actually 3D. Many small layers are positioned in harmony, and as only two of the available axes are used, the third is available to create layered depth effects through parallax.

For more tips, see our Indie Game Dev insider series of interviews with developers.

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