How Portals Are Made in Portal and Other Similar Games / ITech content

Contents:

• Portals before Portal
• How portals work

Teleportation is an important element of many science fiction and fantasy games. There are two main types of teleportation. The first type simply moves the character from one location to another, often accompanied by various effects, such as colored sparks and bright visual elements, to hide the moment of transition. These effects add spectacle and help create an atmosphere of magic and wonder.

The second type of portal is an opening on the wall or suspended in midair. This is an additional door through which the character can move. The unique feature of this method is that the location the character will reach is visible through the portal. The transition between locations is so smooth and seamless that it feels as if the character simply walked through the door.

In this article, we will discuss the final type of portal in games. They are distinguished by a more complex implementation and impressive visual design. Portals not only serve as a functional element of gameplay but also become an important part of the design, creating a unique atmosphere and adding dynamics to gameplay interactions. We will consider their features, advantages and impact on gameplay, as well as examples of successful use of portals in modern games.

Portals before Portal

The Portal series of games by Valve has become iconic and is associated with the unique portal mechanic. However, it should be noted that the concept of portals emerged long before the release of this franchise. The idea of ​​teleportation and the use of spatial transitions in games was presented in various projects preceding Portal. This inspired the developers to create original and innovative gameplay mechanics that won the hearts of players around the world.

The secret level Lunatic Fringe in the shooter Duke Nukem 3D, released in 1996, is an interesting example of unconventional game design. This location is a small cylindrical room with a smaller room in the center. What makes the level unique is that after going around the first room clockwise and returning to the starting point, the player finds themselves in an alternate version of this room. To return to the original space, it is necessary to either go in the opposite direction or continue moving clockwise. Thus, to completely bypass the room, the player must go through it twice. This mechanic creates a captivating and confusing experience that highlights the creativity of the game's developers.

If you stand in the interior room, you'll notice that the windows overlook an alternate version of the level, while the door overlooks the standard version. This contrast creates a unique perception of space and allows you to better understand the differences between the two versions.

The 3D effect in the game is achieved thanks to the features of the Build Engine. This engine creates the illusion of depth, despite the fact that all the game rooms are located on the same plane. For example, when the character falls into a lake and ends up underwater, in reality, an unnoticeable teleportation occurs to a separate room in another part of the map, located on the same level as the other rooms. This helps create unique gameplay situations and maintain player interest in exploring the world.

In Duke Nukem 3D, the water surface acts as a teleporter that moves the character to the next room, creating the illusion of an underwater world. This game design element allows players to immerse themselves in the atmosphere of an underwater adventure, adding unique mechanics and visual effects characteristic of the game.

The game engine operates on the principles of impossible geometry, allowing characters to teleport between rooms located at significant distances from each other. Specifically, the Lunatic Fringe map features two versions of a single cylindrical room. At a certain point, the player is teleported from one version of the room to another, creating a unique gaming experience and adding an element of mystery to the exploration of the space.

Tier Drops operate on a similar principle, but in this case, we are dealing with a spacious square room that can be entered from four sides. Importantly, the character's choice of entrance determines the contents inside. This creates a unique gameplay dynamic, allowing players to explore different options and tactics based on their chosen direction. Thanks to this approach, each entrance becomes not just a starting point, but an important strategic element that affects the entire gameplay.

Speaking of portals that appear as doors and open access to spaces larger than their external dimensions, it is worth mentioning the 1997 Russian shooter MadSpace: To Hell and Beyond. This game features a cube, each side of which leads to a long corridor. Although such geometry is impossible in real life, it has been actively used in video games since the inception of the FPS genre. Game developers are using these concepts to create unique game worlds and experiences, allowing players to explore spaces that defy conventional laws of physics and perception.

Unreal, released in 1998, gained popularity thanks to its multiplayer map mechanics. One notable example is the map DMRadikus, where players could discover a portal located in the center of the room leading to a vast hall. This feature contributed to the creation of a unique gaming experience and solidified Unreal's position as one of the iconic games of its time.

In Unreal, portals are called warp zones and have certain limitations. For example, weapons that use hitscan (a method of detecting hits using an invisible beam emitted from the barrel at the moment of firing) cannot hit an enemy located on the other side of a warp zone. However, projectiles such as rockets, grenades, and disks, which are separate objects, can pass through this zone without hindrance.

When creating multiplayer maps for Unreal, it is important to consider the placement of warp zones. The developers advise avoiding placing such zones in long corridors. This is because players, upon spotting an enemy at the other end of the corridor, will likely equip a long-range weapon, but will be unable to hit their target. Taking these aspects into account can improve gameplay and enhance interaction between players.

Sounds don't travel through the Warp Zone, making it a unique space in the game. If you're playing with bots, they won't be able to detect you when you're outside the portal. This creates unique opportunities for tactical maneuvering and strategic planning in gameplay. Use these features to gain an advantage in the game.

At E3 in 1998, the developers of the shooter Prey demonstrated one of the game's key features: portals. These portals were intended to play a significant role in gameplay, not just serve as decorative elements in levels. This innovative approach to using portals significantly differentiated Prey from other games of the time and attracted the attention of both players and critics.

The first impressive moment of our presentation was the demonstration of the portal mine. This mine opens a portal when thrown, allowing the player to create a unique playspace. We then used her "sister" to open a second portal. During the demo, we threw mines so that the player could see their character through the rift and aim at them. This evoked surprise and delight in the audience.

Paul Schuitema is a key member of the Prey development team. His experience and expertise contribute to the creation of innovative solutions and the improvement of the product's functionality. Paul oversees strategies to optimize Prey's performance, making him a key player in the development and implementation of new technologies.

Let's get to the heart of the development of the first version of Prey. When the game was released in 2006, it did indeed feature portals. However, their functionality was significantly limited. Portals were used to create unique geometry of the alien spaceship, but in general they played more of a decorative role in the game locations.

The portals were attractive in appearance and functioned flawlessly. When the player first encountered them, they caused surprise and slight confusion.

They created many exciting situations. In one scene, for example, we could use a portal to reach a miniature planet enclosed in a glass container. This unique concept adds depth and interest to the story, allowing viewers to immerse themselves in unusual worlds and explore their details.

In 2005, eight students at the DigiPen Institute of Technology developed the game Narbacular Drop as part of their studies. In this game, the player controls a princess who is trying to escape from a dungeon. The princess does not have the ability to jump, but has the unique ability to create portals on most surfaces. Moving through one portal, she emerges from another, which allows her to overcome various obstacles in each level. Thus, Narbacular Drop is an original puzzle game that combines elements of strategy and logic, offering players an exciting gameplay.

Portals in games are not a new concept, but the way the students were able to integrate them into the core gameplay deserves recognition. The ability to create portals on virtually any surface opens up new horizons for gameplay, which was announced, but not implemented, in Prey. This solution not only enriches the gaming experience, but also provides players with unique opportunities to explore and interact with the world around them.

The students developed the game with the intention that it would become part of their portfolio and help with future employment in the gaming industry. This plan turned out to be more successful than they expected. When Gabe Newell, Valve's CEO, saw their project, he decided to hire the entire team, offering them the chance to create a similar game, but at a more professional level—using the Source engine, rather than a home-made one that required some work. Thus began the development of the famous game Portal.

How Portals Work

Portal is a unique game in which the player controls a portal gun capable of creating two portals on different surfaces: blue and orange. Using this mechanic, reminiscent of the game Narbacular Drop, the player can move between rooms, solving complex puzzles. The main goal of the game is to escape from the evil artificial intelligence GLaDOS, who not only dislikes humans but also enjoys creating torturous challenges using the portal gun. Portal stands out for its originality and deep concept, offering players an immersive experience in solving puzzles and interacting with the world around them.

There are numerous materials available online explaining the creation of portals, through which you can look as if through an open door. The developers of the game Portal also provided comprehensive commentary and explanations revealing the details of this effect during gameplay.

The effect is achieved using multiple cameras. The main camera is attached to the protagonist, allowing us to see the world through her eyes and creating an image outside the portal. The second camera is fixed on the portal we will exit through if we enter the one we're looking at. It is this camera that creates the image we see through the portal. Thus, the game's image is rendered twice, creating a unique visual atmosphere and enhancing immersion.

An important point is that the position and angle of the second camera relative to the portal to which it is attached are set in the same way as the position of the main camera relative to the portal it is facing. This ensures consistency in the images received by both cameras and ensures a more accurate perception of space. Proper camera positioning is critical to creating high-quality visual content and improving user experience.

Teleportation is a subtle and seamless movement of a character from one point in a level to another, occurring when approaching a portal. This technology is based on the correct configuration of two cameras, which allows the player to seamlessly merge the image from the second camera with the image from the first camera. This creates the effect of instant movement and enhances immersion in the gameplay, making interaction with the game world more natural and dynamic.

When rendering the image that the player observes through a portal, it is necessary to use a virtual camera directed through the opposite portal. To achieve an accurate result and improve rendering efficiency, we render only those objects that fall within the limited field of view of the opposite portal. Objects located between the virtual camera and the plane of the opposite portal are excluded from rendering. This approach allows us to optimize the process and improve the quality of images displayed in the game.

David Kirchner, a programmer who participated in the development of Portal, shares his thoughts in the developer commentary mode. His insights help players gain a deeper understanding of the game creation process and the specifics of game design.

Objects that are not visible during rendering, including walls, play an important role in the visualization of scenes. When a second camera is placed behind a portal, it appears behind the first camera, which can affect the perception of the image. There are two methods for outputting the image from the second camera to the first portal, allowing for effective rendering control and improved visual quality. Proper use of these methods can significantly improve performance and scene realism.

The first method involves displaying the image on the portal texture, similar to how it is done on a TV screen. However, this approach has a drawback: the image may look fine from a distance, but upon closer inspection, texture pixels become visible. Increasing the texture resolution can help alleviate this problem, but it will also significantly reduce system performance. This is especially true if the portals are located opposite each other, creating the effect of an endless tunnel. Initially, the developers used this method, but it was soon abandoned due to its high load on video memory.

The second method for creating portals in Portal is based on the use of a stencil buffer. This specialized buffer is present on the graphics card and allows for effective control of image display. In the context of Portal, it's important to note that both cameras render full-screen. However, the image from the second camera is only displayed within the area occupied by the portal. Thus, the portal acts as a stencil within which the game correctly draws the necessary pixels. This solution ensures realistic transitions between worlds, a key element of gameplay.

The recursion that occurs when portals interact is an interesting aspect of the gameplay. To optimize performance, the developers limited the number of recursion iterations to nine. The infinity effect is achieved by copying the image from the previous frame to the last portal in the recursion chain. This solution allows you to create the illusion of infinite space without overloading the system with unnecessary calculations.

When creating portals, there was a problem: how to avoid hitbox collision A player collides with a wall with a second portal installed on it while teleporting? This task requires careful design of the movement mechanics to ensure a smooth and seamless transition between portals. Solving this problem is critical to creating an engaging game experience and preventing unwanted collisions that could disrupt the gameplay flow.

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Integrating portals into the Source engine's physics system is a complex process that requires several iterations to achieve the optimal balance between performance and accuracy. Portals can be placed anywhere in the game world, which required modifications to the physics system. This allowed for dynamic geometry changes to calculate collisions between walls and floors and objects located on the opposite side of the portal. This approach ensures realistic object interactions and improves the overall gaming experience.

David Kirchner, a programmer at Portal, shares his thoughts and experiences within the game mode with developer commentary. His contributions to the project significantly influenced the development of gameplay and user interaction. Kirchner discusses key aspects of development, including game mechanics, and the impact of player feedback on the final product. This mode provides a unique opportunity for players to learn behind the scenes of the creation of Portal and see how industry professionals approach solving various problems.

The difficulty was that Initially, the system resized the wall's hitbox to accommodate an object entering a portal in 500 milliseconds. Although this is only half a second, this delay was noticeable during testing. As a result, the developers developed a new system that creates a temporary hybrid physics environment around the portal. This environment allows for collision calculations with less precision than the Source engine. However, the calculations proved accurate enough for portals to function correctly. Thanks to this, the surface's hitbox is now resized in just ten milliseconds, significantly improving performance and responsiveness.

During the development of the second part of the game, portals found practical application. The developers were faced with the need to constantly change the connections between rooms to achieve the desired level of complexity and spectacle. This process sometimes took hours, and sometimes days. As a result, the team decided to develop rooms that would not have direct connections to each other. The transitions between them were achieved using the portal mechanic, which significantly simplified the level design process and allowed us to focus on creating a unique gaming experience.

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By using portals to connect different areas of the world, we were able to create spaces with unique geometry. You could peer into an adjacent room through a corridor located at one point in the map, while the room itself was located in a completely different place. We easily integrated elevators, vast spaces, and rooms whose interior volume exceeds the exterior. In addition, we were able to implement the concept of an infinite fall by connecting the shaft to itself. As a result, each connection between different spaces became a portal, opening up new possibilities for exploration and interaction.

Erik Tams, one of the developers of Portal 2, shares his thoughts and ideas in the commentary mode. His contribution to the creation of this iconic game is invaluable, and it is thanks to professionals like him that players can enjoy a unique gaming experience. In the commentary, Eric reveals development details, discusses complex moments, and shares interesting facts that make Portal 2 even more engaging.

In Valve documentation, such portals are referred to as linked_portal_doors or world portals. These elements have no visual effects and are simple quadrangular shapes. Players can even use the portal gun to shoot through them, which adds an interesting element to gameplay and opens up new strategies for interacting with the environment.

During the final stages of development, most portals were removed to ensure proper connections between rooms. However, such portal doors are still present in some places. An example is the scene with GLaDOS's awakening, in which a portal connects the incinerator shaft to GLaDOS's chamber.

Since the release of Portal, the gaming industry has not seen any projects that have attempted to reproduce similar gameplay. However, teleportation mechanics continue to find widespread use, particularly for creating unusual spatial geometry. A striking example is the 2013 game Antichamber, which uses portal mechanics to create spatial illusions. Similar techniques are used in 2019's Manifold Garden, demonstrating how teleportation can enrich gameplay and add puzzle elements.

The Stanley Parable, released in 2013, uses portals to create looping locations and to ensure that returning to a previous point does not lead the character to the starting point. This approach allows players to experience a sense of disorientation and explore the game world from a new perspective. Similar mechanics can also be seen in the 2020 puzzle game Moncage, where unconventional spatial solutions and spatial perception play a key role in the gameplay. Both games showcase original uses of portals, pushing the boundaries of traditional gameplay and offering players a unique experience.

Portals offer a wonderful opportunity for creative expression. Often, players are unaware that characters are moving through these magical passages.