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Portal is Valve’s professionally developed spiritual successor to the freeware game Narbacular Drop, the 2005 independent game released by students of the DigiPen Institute of Technology; the original Narbacular Drop team are now all employed at Valve. Certain elements have been retained from Narbacular Drop, such as the system of identifying the two unique portal endpoints with the colors orange and blue.

A key difference in the signature portal mechanic between the two games however is that Portal’s “portal gun” cannot create a portal through an existing portal unlike in Narbacular Drop. Portal took approximately two years and four months to complete after the DigiPen team was brought into Valve, and no more than ten people were involved with its development.

Portal writer Erik Wolpaw, who along with fellow writer Chet Faliszek of the classic gaming commentary/comedy website Old Man Murray were hired by Valve for the game, noted that “Without the constraints, Portal would not be as good a game.”

Portal Gun [Concept Art / Proto]:

Images still at Portal on Steam Store, Notice that some differences are:

• The Colors of Portal gun was still in beta, but Portal Gun was changed.
• Graphics looks a little better.
• The Portals graphics was a lot of different.
• When the portal gun shoots and open the gate, the graphic was a lot of different, there was more effects

The Portal team worked with Half-Life series writer Marc Laidlaw on fitting the game into the series’ plot. Wolpaw and Faliszek were put to work on the dialogue for Portal. GLaDOS was central to the plot, as Wolpaw notes “We designed the game to have a very clear beginning, middle, and end, and we wanted GLaDOS to go through a personality shift at each of these points.” Wolpaw further describes the idea of using cake as the reward came about as “at the beginning of the Portal development process, we sat down as a group to decide what philosopher or school of philosophy our game would be based on. That was followed by about 15 minutes of silence and then someone mentioned that a lot of people like cake.” According to Kim Swift, the cake is a Black Forest cake which she “thought looked the best” at a nearby bakery.

The austere settings in the game were a result of finding that testers spent too much time trying to complete the puzzles using decorative but non-functional elements; as a result, they minimized the setting to make the usable aspects of the puzzle easier to spot, using the clinical feel of the setting in the film The Island as reference. While there were plans for a third area, an office space, to be included after the test chambers and the maintenance areas, the team ran out of time to include it. They also dropped the introduction of the “Rat Man”, the character that left the messages in the maintenance areas to avoid creating too much narrative for the game.

The textures of the Old Portal Gun are still found in game files, however, the Purple and Blue color was changed to the original (orange and Blue):
*Click to Enlarge*

GLaDOS [Concept Art]:

The player’s model was at the beginning a male character, but then it was changed for the actual female character known as Chell. Chell’s face and body are modeled after Alésia Glidewell, an American freelance actor and voice over artist, selected by Valve from a local modeling agency for her face and body structure. Ellen McLain provided the voice of the antagonist GLaDOS.

Erik Wolpaw noted that “When we were still fishing around for the turret voice, Ellen did a ‘sultry’ version. It didn’t work for the turrets, but we liked it a lot, and so a slightly modified version of that became the model for GLaDOS’s final incarnation.”

Mike Patton’s voice also appears in the game performing the growling and snarling of the final core-chip of GLaDOS. The Weighted Companion Cube inspiration was from project lead Kim Swift with additional input from Wolpaw from reading some “declassified government interrogation thing” whereby “isolation leads subjects to begin to attach to inanimate objects”;

Swift commented that “We had a long level called Box Marathon; we wanted players to bring this box with them from the beginning to the end. But people would forget about the box, so we added dialogue, applied the heart to the cube, and continued to up the ante until people became attached to the box. Later on, we added the incineration idea.”

GLaDOS Protos:
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According to Swift, the final battle with GLaDOS went through many iterations, including having the player chased by “James Bond lasers”, which was partially applied to the turrets, “Portal Kombat” where the player would have needed to redirect rockets while avoiding turret fire, and a chase sequence following a fleeing GLaDOS. Eventually, they found that playtesters enjoyed a rather simple puzzle with a countdown timer near the end; Swift noted that “Time pressure makes people think something is a lot more complicated than it really is”, and Wolpaw admitted that “it was really cheap to make [the neurotoxin gas]” in order to simplify the dialogue during the battle. [Infos from Wikipedia]

In the beta trailer below, you can notice many rooms that were removed or heavily changed from the final game (also, the portals look different). The game seemed to originally have a more dark color scheme.

Video [Beta Trailer / Gameplay]:

Unused Stuff

This game contains some beta unused stuff, some of those images appeared in trailers, such as Red Portal, and the Effect of the Red Portal:

There was one unused sign that was never saw in any trailers, a sign with a Joke of the 300 Movie. It might be rejected due to copyright issues:

There is also a Unused GLaDOS voice in the game files, would might be used at the end of the game:

Thanks to FullMetalMC and Gabrielwoj for some of the images!
Also Thanks again to Gabrielwoj for the unused Stuff!