CGSociety :: Game Production Focus
15 July 2011, by Paul Hellard
Valve Software's Portal games are based around a deceptively simple concept: using a 'portal gun' the player is able to open a hole in space that connects two locations in the world in an otherwise impossible manner.
By moving through one portal, you emerge from the other portal no matter where it is. This has allowed the development crew to craft all sorts of exciting, brain bending puzzles for players.
In the move from Portal and Portal 2, The player takes on the role of Chell, a test subject trapped in a diabolical labyrinth of test chambers run by an insane computer AI named GLaDOS. The player's aim is to use their portal gun to solve puzzles and ultimately escape from their entrapment. Along the way they explore the incredible interiors of the testing facility and meet other characters who can help them.
"Our process at Valve is very much built around the idea of collecting people on a team and making sure we always have a diverse mixture of disciplines working closely together to solve problems and build the game," says Josh Weier, Project Lead on Portal 2.
"We believe that the people doing the work on an area of the game should also be the ones driving the design and making decisions around it, so artists attached to a specific area of the game had a great degree of freedom to create and build the world they were working on. Team members came from all over Valve depending on what was needed for the project, from concept to texture artist."
The Portal 2 designs grew from the stark look created in the first Portal title. That environment was very sterile and devoid of color and organic shapes. Part of Valve's goal with Portal 2 was to take this very clean and precise environment and break it down, age and destroy it to give contrast to the first game.
This is most obviously visible in the test chambers that are overrun by vegetation or large-scale destruction. This direction allowed them to increase the visual fidelity of the environment greatly, while still remaining familiar to players of the first game.
In some instances, concepts were taken from the first game and expanded, giving them much larger roles in the sequel. The animated robotic arms that help dynamically to build the test chambers are a good example of this. In the original Portal the walls were crude modular panels put in place by rough pistons.
By extending this concept into the animated and highly articulate robotic arms, Valve artists were able to give a lot more life to the environment, as well as making it another character in the world rather than simply a passive barrier.
In the original designs for Portal, Valve tried to place the puzzles into real-world settings like office spaces and other plausible set pieces a player would expect to find in a scientific research facility. This created a great deal of trouble, however, because the puzzle spaces often required very contrived situations for gameplay reasons.
So after a lot of wasted effort trying to create believable spaces out of mostly unbelievable (but necessary) configurations, the team decided to embrace the more abstract nature of the puzzles, which created the look and feel for the 'test chamber' areas throughout the game.
The first Portal could be roughly broken down into two main areas: these 'test chambers' and the 'out-of-bounds' areas behind those walls."For the sequel, we wanted to flesh out and expand these areas while also adding new environments that players wouldn't be expecting. We do this in the first moments of the game by starting the player trapped in a rundown old motel room.
Players quickly discover that this motel room isn't what it appears, and we take them on a frantic ride through a part of the facility they had never seen before."
"We also wanted to explore the history of the facility. The player's route takes them through long-abandoned sections of the labs," artist Randy Lundeen explained. "These are huge vertical shafts carved out of an old salt mine and containing massive, stacked spheres that house the test chambers.
"We did a lot of research into actual salt mines as well as underground neutrino detection facilities. The 'buried past' theme also let us have some fun showing the company's slow decline from its optimistic beginning to bankruptcy and corruption. The player literally walks through forty years of history."
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The core portal mechanic in the game is built around placing portals onto surfaces in the world. Surfaces fall into one of two categories: 'portalable' or 'non-portalable', meaning that a portal can or cannot be placed on the surface, respectively. It's critical that players be able to enter a space and immediately understand which surfaces fall into which of the two categories.
Failure to understand this causes players to thrash around the spaces, unsure of how to proceed and they becoming frustrated.
"We used many metrics to try to give players hints about how a surface would react to their portals. Porous surfaces, light in value, flat in texture and with non-reflective surfaces were always portalable surfaces. On the opposite end, surfaces that were dark in value, looked hard and shiny to the eye, or were bumpy or irregular were always non-portalable," says Jeremy Bennett, another talented Portal 2 artist.
"We took a lot of inspiration from reference pictures we had of old Russian Soyuz spacecraft. This let us develop textures that looked highly technical, but were still immediately readable to players," Bennett continues.
These textures were first generated in 3D packages. Variations and stains were then painted in Photoshop. Many of the other textures in the game began as swatches of colors painted by hand so they could be quickly placed into the game for assessment in their target environments. As detail was added, the spaces in the game slowly became more and more fleshed out until they were complete.
This process builds the art alongside the gameplay, assuring that the colors and textures were correct for their application.
When designing the two-player cooperative portion of Portal 2, Valve wanted players to inhabit and control two robotic characters, rather than the human character played in the single player portion of the game.
Objects in the Portal world have a distinct aesthetic. By basing the concept pieces around specific 'Portal shapes', Valve artists were able to very rapidly close in on two particular designs selected as favorites. The first was the 'ball bot' design which would evolve into the Atlas character.
The main component of Atlas is modeled after the 'personality cores' found in the game. The second robot, 'P-Body' was based around the turret characters found throughout the game.
"By using these shapes, the robots were immediately grounded in the style of the game and afforded more opportunities in the fiction of the world. The robots needed to feel as if they were cobbled together by the maniacal artificial intelligence controlling the facility", explains artist Tristan Reidford.
Once the basic look was settled, the modelers and animators worked together to properly rig the characters for all the animations they wanted to achieve. Because these were robotic characters, the animators wanted to give them a range of motions that were unique and distinctly inhuman. The modelers were then able to use these requirements to build the armatures and joints of the robots to look and move plausibly through all the various ranges of motion that were required.
By letting their form follow the desired function, the robots' bodies were able to be crafted in a very believable manner with a high degree of mechanical accuracy.
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Valve's Portal games are required to run at a very high frame rate on a variety of computers and video game consoles (Xbox 360, Playstation 3, etc). This means that the density and complexity of the art created is sometimes too much for those machines to handle effectively, and what is required is called a 'perf pass' to bring them within performance requirements determined with the help of the project's graphics programmers. This often means making painful cuts in visual fidelity or density and quite a bit of work to hide these cuts and deliver a high-quality visual experience.
Portal was unique because the addition of the portals in the world means that the engine can very quickly be drawing the same scene multiple times. If a player looks through a portal, they'll be seeing the world in front of them and also the world through the portal.
If that portal can see its paired portal, the engine is suddenly drawing the world three times over. If you add to that the two-player co-op, which can have four portals simultaneously, plus reflective water surfaces and split-screen rendering, the engine can very quickly be drawing the world up to sixteen times per frame.
This required the Valve Software team to do more graphical optimization that any game they've created previously, including finding methods for creating 'world imposters' which baked portions of the scene into rough model geometry that can could selectively turn on in graphically intense scenes.
Portal 2 was based on the Source engine that has been developed at Valve. This is the same core technology that's driven Left 4 Dead 2 and Team Fortress 2. The biggest difference this time around has been the use of dynamic lighting, which allows the contrast and tone of the game to be drastically changed in comparison to other titles.
The Source engine uses a pre-computed method to calculate radiosity lighting in the different levels, which is baked into lightmaps. The addition of dynamic lighting, with smoothly rendered dynamic shadows, allowed the lighters to augment that radiosity lighting with high-contrast spotlights. This created a very different look than the typical Source engine game.
The radiosity produced great details in the low end of the dynamic range, while the spotlights provided very intense contrast in the higher end of the range, along with very detailed shadows that could interact in real time with the various elements in the world. These features were utilized heavily in conjunction with the articulated robotic arms that could come to life and interact with the rest of the world right in front of players. The dynamic lighting allowed them to tie these elements more strongly into the scene than would have been possible with just radiosity lighting.
The original Portal had a very cold, sterile environment. The objects that the players interacted with (buttons, cubes, doors) were some of the only things in that world with any sort of color. This was a very deliberate choice to help players identify what was necessary for completing each test chamber.
For example, the buttons that players needed to place cubes onto were bright red, which made them visually pop out of their surroundings. Shape also aided identification, and objects the player could interact with were often rounded and circular to help them stand out against the otherwise very rectilinear backdrops.
In Portal 2, the hue of the lighting in the world slowly shifts as the player progresses through the game. At first, the light is very warm in hue, scattering in from the ceiling to emulate the sun near the surface of the facility. As the player descends deeper into the facility, the lighting slowly changes in hue to a cooler blue, helping provide the feeling that they're moving further and further away from the surface.
In the lowest portions of the facility, the player is taken through three distinct time periods in the facility's history. Players begin in the mid-1950s before progressing through the 1970s and finally the mid-90s. A great deal of signage, color, and typography is used to help sell this movement through time. Valve Software's Portal 2 is a huge triumph of design, engine optimisation and a huge load of talent by a team proving themselves time after time. If you ever get a chance, buy this and expect some great laughs.
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