Radix

Keeping with tradition, I'd say it's about time we took a look at what our community has achieved throughout the year. If last time I was saying how 2017 was a year of immense growth, then 2018 was surely one of significant change. And it hasn't been without its troubles and anxious moments. No change ever is, but I believe it to be for the best. We've seen some of our friends become parents, change work fields or get their first job in the industry. We've even seen a few pursue their dream projects. And for that, we have to applaud them. It takes courage to keep moving forward and to realise when it's time for something new. In the meantime, I hope this article inspires you and I wish everyone 
good luck!
 
2018: Mapcore's Year in Review
 

SteamVR - Gulping Goat Space Farm
by @Steve, @marnamai, @The Horse Strangler, @Sersch and others at Scraggy Rascal Studios
produced in collaboration with Valve
"Scraggy Rascal has been working with Valve to create all new SteamVR content, we've been given a lot of liberty to create these locations. Our goal was to create interesting and fun locations for the player to explore. These projects, over the last couple months, have been a crash course in Source 2,VR, project management, delivering within deadlines, working together as a team and personal growth. It has been an invaluable experience and great opportunity ... and we're just getting started!" - marnamai
 

Darksiders III - Art
by @The Horse Strangler and others at Gunfire Games
"Probably one of the biggest challenges the artists and designers faced on Darksiders 3 was working with both a platforming and fully connected streamed world. This meant that everything exists all the time. While we streamed levels in and out, areas couldn't intersect and we couldn't do the classic "Small exterior, big interior" swap. This was especially challenging because of how much verticality our design must support. We had a few "vistas", but for the most part every aspect of the level was accessible. If you can see it, you will likely be able to get there, jump on it, fight around it, etc. Fury, the main playable character can double jump, swing, float, glide and even rocket jump over 10 meters high. Personally for me it completely changed how I looked at art filling up a space. Every single mesh we placed impacted design. Art was design, and design was art." - The Horse Strangler
 

Europa
by @[HP]
"Europa is a relaxing narrative experience. The goal with this game is to offer just enough challenge that its rewarding to get from one area to the other for more than just the visuals by using environmental hazards, platforming sequences and light puzzles that you can beat by exploring.The game is split into linear sections and wider areas, that's at the core of the game and as you play, you keep improving your characters moving ability, which will further exploration and give you the ability to solve newer light puzzles. There's none of the typical character upgrading systems, rather, the levels will offer the incremental challenges and the sense of progression. Europa's main focus lies in environmental storytelling and immersing the player in it's universe with passive storytelling, evoking awe and bliss with colorful watercolor-like art and music." - Helder Pinto
 

Counter-Strike: Global Offensive - Turnpike
by @Squad
"For a while the "Highway Restaurant" theme has been sitting in my little Concepts.txt file. When the Wingman Contest was announced, it felt like the perfect opportunity to turn this idea into a map, as its relatively small size would be fitting for the Wingman gamemode. The casual nature of Wingman made me add some elements that I would not normally add to, let's say, a Defusal map, like the TF2-esque team color coding (albeit subtle), the moving vehicles and the silly bomb target. Additionally, since the playable space is (almost) completely indoors, making it nighttime felt right, as it both emphasizes the interiors and makes for an atmospheric blorange background." - Squad
 

Dying Light - A New Hope
by @will2k
"A full-fledged custom single player campaign that ties in to the original story of the main game. It will see the main protagonist, Kyle Crane,leaving the City for the countryside to search for a specific elusive medicinal herb and bring it back to Dr. Camden who believes it could be the cure to the Harran Virus. This campaign is a one man show as I’m doing everything myself: level design, environment art/detailing, story creation, scripting/quest creation, custom dialog, custom audio, custom materials/textures, custom foliage systems, custom brushes for terrain painting/sculpting, lighting, manual nav mesh tuning, scripted NPCs…" - will2k
 

Prodeus
by @General Vivi and Michael Voeller
"Prodeus is the first person shooter of old, re-imagined using modern rendering techniques. Oh, and tons of blood, gore, and secrets. Creating Prodeus has meant a lot to us over the last year. It feels great to finally be doing something for ourselves. It can be pretty ambitious at times since there are just two of us, but I’m confident we can pull it off. Keep an eye out for the end of February for a big announcement." - General Vivi
 

Counter-Strike: Global Offensive - Ruby
by @catfood
"When I was on vacation in Portugal years ago I was so impressed by the city Lisbon that I really wanted to build a map that has the same vibe. At the time I was already working on different projects so I decided whenever I got enough time to work on a map this size I would go back. So early 2017 the moment was finally there, I went back to Lisbon to shoot (~2000) reference photos then made a list of things that are iconic for Lisbon and started working on Ruby. Adding a lot of height differation, warm colors, tile patterns and ofcourse trams was essentiental to get the Lisbon vibe." - catfood
 

Subnautica
by @dux, @PogoP and others at Unknown Worlds Entertainment
"A mix of Survival, story, mystery, resource gathering, base building with some accidental horror and plenty of deep, deep water. We had not long finished up with Natural Selection 2 and were hungry to develop a different kind of game. During development we were (and still are) a small team but the game kept getting bigger and grew into something far larger in scope than originally planned. So we soon realised that what we had could be turned into something really unique if we put our heads down and just cranked on it." - dux
 

Unreal Tournament 4 - Chamber
by @Ubuska
"I used Halo and Warframe artstyle as a reference. The goal of this project was to make fun and cool looking map with 100% custom art that is 100 mb in file size. To achieve that I used several advanced techniques such as custom vertex normals, deferred mesh decals, no bake, tiling base materials and masks. There are basically 5 or so texture maps used in the entire map,  most of the filesize space was taken by lightmaps. I learned a lot doing this project in terms of composition, art direction and optimization. Hope you enjoy this map as much as I do!" - Ubuska
 

Counter-Strike: Global Offensive - Pitstop
by @Quotingmc and Quadratic
"It is not often that CS: GO receives a new game-mode, especially one as competitively focused as Wingman. I was understandably pleased at the announcement of the 2018 CSMapMakers contest for the mode. Pitstop was my entry where I set out to create a thematically bold centre piece for my portfolio. With the help of my teammate Quadratic and support from multiple Mapcore members, I learnt a lot about taking a level from a simple blockout to completion; I can say for certain I’m thrilled with the end result!" - Quoting
 

Black Mesa - Xen
by @JeanPaul, Adam Engels and others at Crowbar Collective
"While building Xen we had to design, iterate, and iterate (then iterate some more). We took what we thought we knew, and put it to the test. We learned how design and scope work together, and how to build momentum as a team. We are extremely proud of what we have accomplished over the year(s)! Despite the long and occasionally frustrating timeline, it has been a real testament to the commitment that this team and this community have for Half-Life." - Adam Engels
 

Unreal Engine 4 scene
by @Vorontsov
"So I decided I would step out of my comfort zone and create a small environment in an engine I've never used before, UE4. Although I think I did a fairly decent job at the time there were ultimately many nuances I could have done better, but that is the artist dilemma. This project taught me the value of properly blocking out your environment, gathering as many references as you can and to have patience and not rush through assets, when breaking any of these rules I was punished for it. Stay tuned for my next project which will be a giant mech, coming soon Valve time TM." - Vorontsov
 

Counter-Strike: Global Offensive - Opal
by @MikeGon
"My goal with this project was to make a fun and compact defuse map, with a simple level flow, ample verticality, and an overlapped layout! I wanted to have interior and exterior, and break the grid a lot, to avoid having that "90 degrees grid" feel in the layout. I needed to have a vista on one side of the map to help with orientation, so I decided to make it a coastal town, inspired by those found on the island of Skopelos, Greece. Expect more updates in the near future, as I'm not yet satisfied with it. Since this is my only CSGO map, I want to put all my time and effort into it, and focus on quality instead of quantity. Thank you everybody for your support and feedback! <3" - MikeGon
 

Insurgency: Sandstorm - Precinct
by @Xanthi, @Squad, @Jonny Phive, @LATTEH, @Steppenwolf and others at New World Interactive
"Precinct, was a fun and challenging map to work on. We decided early on to melt District and Contact two of our very nostalgic maps together into a single large-scale urban environment. The goal was to preserve the nostalgic feeling and at the same time create something unique and fresh not just a 1:1 copy. In the block-out stage we started playing with different terrain heights, which eventually was the key to accomplish our goal. Terrain height was a bit of a trial and error process; I remember driving up a hill and not having enough torque, oops!!" -Xanthi
 

Counter-Strike: Global Offensive - Killhouse
by @FMPONE
"Killhouse showcases brutal duels, player reaction times, and close-quarters combat. A highly vertical layout ensures the sort of unpredictability and replayability ideal for CS:GO’s 2vs.2 "Wingman" game-mode." - FMPONE
 

Counter-Strike: Global Offensive - Station
by @Roald and @untor
"All experiences contribute to where I am at this point. I am just a hobbiest but I think I learned alot about level design just by doing it and enjoying it. Overal my goal is to improve myself on level design, but also enviorment art. I think I archieved a goal on level design and it's now time to continue on enviorment art. This is where untor morozov comes in. I have met untor a while ago. He made this map 'Waterfall' which was pretty populair. I liked his designs and added him as a friend. When I had this wingman map going on with positive feedback I just contacted him again to work on it with me and since this moment we have had a incredible teamwork. I am gameplay orientated and he is art orientated so we were a great couple. We just enjoyed work on this project and respected eachother and had alot of fun." - Roald
 

The Gap
by @Yanzl and Sara Lukanc
"The Gap is a sci-fi thriller first person narrative exploration video game. You play as Joshua Hayes, a neuroscientist trying to figure out what happened, barely remembering anything about his past. It started as a project for our BA thesis and has now grown into a standalone game. It's also my first "real" indie game project, helping me learn a lot about Unreal Engine 4 and game development in general." - Yanzl
 

Counter-Strike: Global Offensive - Alexandra remake
by @Serialmapper
"My first successful map was born 10 years ago for CS1.6. It was done in just 4 days. Since then it has been ported/improved several times on CS:S then finally on CS:GO. It always had a "dust" theme. Initially i wanted to remake it with an "inferno" style but when the new dust2 came i switched the plan to use the new assets. The map was and is frequently played on public servers especially in Eastern Europe so i had plenty of feedback to improve it. For some it's just another "dust" map, but for me it's my dust2." - Serialmapper
 

Far Cry 5 - Wetland Turmoil
by @grapen
"I wanted to try working with location design in an (imaginary) open world game for the first time, so I made this backwater cabin neighborhood. At the time I also wanted to see what the limits were in Farcry Arcade and how far I could push it. The level has fixed spawns (a limitation of the editor), but I toyed with the idea of making it work regardless from which direction the player would have approached it. The pathing and player guidance is more or less shaped like the number eight, with the church acting as an outlook. Your task is to eliminate all the bad guys. In the end I wanted to do so much more, but couldn't due to technical limitations. All in all it was a fun experience to make it." - grapen
 

Counter-Strike: Global Offensive - Trailerpark
by @OrnateBaboon and @Skybex
"We wanted to make a map for CSGO, using a theme that had not been seen in any previous version of Counter-Strike.The map had to incorporate everyday plausibility, provide for enough variety so that things remained visually interesting,  but also be flexible enough to allow for the use of low geometry for easy grenade strategies. Being able to immediately recognize a theme in a map is always important, so with all this criteria in mind, A trailer park fitted the bill perfectly. There is still some way to go before a full release, but 2018 was a great year for progress on this project." - OrnateBaboon
 

Unreal Engine 4 scene
by @Corvus
"I was inspired by games like stalker and the last of us. The goal was to make something photoreal with a lot of foliage. It took a couple of iterations but I think I achieved the goal in the end. While making this project I've had to learn a lot about Speedtree to make all the foliage, it was a really cool experience. Right now I'm in the army so unfortunately I can't make any more scenes right now, but after I'll come back I'll try to make more scenes like that." - Corvus
 

Overwatch - Busan
by @Minos, @[HP], @PhilipK, @IxenonI, Phil Wang, Lucas Annunziata and others at Blizzard Entertainment
"Busan was a challenging map to make. Due to the game having 12 different heroes on screen we have a somewhat limited memory budget for maps, that includes all models, textures, effects, collision data, lighting information, etc... Fitting three radically different areas (Downtown, Sanctuary and MEKA Base) into one single map budget required us to find new ways to optimize our work. In the end, we were even squeezing kilobytes out of collision data to make it all fit, no kidding! But the result speaks for itself, the map was fun to work on and we are very proud of what we accomplished!" - Minos
 

Counter-Strike: Global Offensive - Highlands
by @ElectroSheep, @El Moroes and @'RZL
"We wanted to make a map in Scotland because, thanks to dishonored 2, we were browsing a lot of references froms this area and we really loved it. I also went myself here in holliday after that. We asked one of our close friends to make some special props, like the police van, the taxi, the phonebox and some others. Unfortunatly the hard development of Dishonored 2 put us in a difficult state where we weren't able to work on the map. So we lost motivation. Then RZL contacted us because he didn't want the project to die so we gave him the keys. And RZL became busy too ^^. Life sometime say NO I guess, hehe. Now Highlands Is my only advanced project I still didn't finished and I'm ready to give it a try, I hope." - ElectroSheep
"Highlands...is this map is a joke? Certainly no but we can say that the development is quite longer than what we expected. Perhaps we learn well how the famous "Valve time" works? :p No seriously I think we can explain that with the motivation. Of course we were motivated to create something cool with this map but with the time and, I think, with what we live in our life we never took the time to do it correctly...I mean we never had a constant rythm on the map. This (and other personal things) led to the current statut of the map; a still "work in progress" map started in 2014. But ElectroSheep came back and his goal is to finish it, and because he's right, I'll come back too to help him. Just, be patient (again) ;)" - El Moroes
 

Battlefield V - Fjell
by @Puddy, @Pampers and others at DICE
"Fjell was an explosive experiment which paired a new Battlefield dynamic, planes and infantry only, with an epic gosh darn mountain top. Tackling this design combination was like dealing with a bear after you've kicked it in the balls. It was a fun challenge and even though its extreme gameplay is quite polarizing when compared to more middle-of-the-road maps, I am happy that we went there!" - Puddy
 

Counter-Strike: Global Offensive - Iris
by @BubkeZ and @Oliver
"Iris was born out of a shared interest in the TV-show "Seinfeld", funnily enough. One day BubkeZ noticed I had changed my Steam profile picture to a photo of "George Costanza" and just like that the wheels were in motion! In the beginning, BubkeZ had the vision of an old city environment with lots of dirty alleyways and brick architecture. We didn't want to fall in the trap of making the map look too bleak, so we came up with the idea of making a mid-century town set in autumn. While the map certainly have visual elements from the 50's, I would say the overall theme of Iris is american auto-industry. Making the old cars was definitely my favorite part of making this map!" - Oliver
 

Unreal Engine 4 scene
by @Brightness
"I have always been a fan of retro and vintage, so this was like a dream to me. After watching the first season of True Detective, I immediately fell in love with the office set and the way the series was shot. I have definitely learned a lot from this project, mostly lighting techniques that can fill your scene with a story. The goal was to recreate their environment in my own style, and I'm pretty satisfied with how it turned out. I definitely wasn't expecting this much of positive feedback and I'm really thankful for this community. I want to do something with the environments, not just as a portfolio piece, but make a short film or make a small adventure game out of them." - Brightness
 

Counter-Strike: Global Offensive - Insertion 2
by @Oskmos
"Being the follow up to the first Insertion it will have the same overall concept with the spawning and open-world like layout. However this time it will be a more urban setting and overall higher quality art assets. I always love to make environments that feels real. And that are familiar. Its all made up. But the details and various elements in Insertion 2 is from my childhood basically. Friends that grew up in the same place I have recognizes it aswell." - Oskmos
 
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The Door Challenge

Submission thread
 
Articles

Designing Highly Replayable Stealth Levels for Payday 2

Level Design in Max Payne: Roscoe Street Station

Effect and Cause - Titanfall 2 Level Breakdown

2017: Mapcore's Year in Review
 

Hurg smiles upon you all!

The Making of Murky Station: Payday 2
Payday 2 is a four player cooperative first-person shooter with RPG elements that centers around robbing banks and stealing rare loot. It was released on August 13, 2013 and has since shipped over 50 DLC packs and counting. With a thriving subreddit, it has consistently been in the top ten games played on steam. Today, I wanted to talk about my adventures designing stealth levels for Payday 2 before leaving Starbreeze in January 2018. While parts of this article are specific problems and solutions for Payday level design, I made sure to discuss them in a broader sense. The skill level of this article is for junior to mid-tier level designers, if you are a senior designer some of this article may sound familiar to you.
I'll start off by saying that Payday's stealth mechanics are not perfect and can be flawed in some areas, but I wanted to focus on the decisions behind the map design, specifically for the heist Murky Station. I'll also break down how we consider using RNG (randomization), and the ways we apply it to objectives and mechanics to keep the level fresh and replayable. This map took 6 weeks to make between 2 people. My partner took the role of Level Builder / Environment Artist and I took the role of Designer / Scripter. Between the two of us, we figured out the scale of the project based on the needs of our studio. The idea was to create a small heist that took around 10-15 minutes to finish with high replayability. There's a lot to go over, so let’s get started!
 

 
Let's start from the beginning
Before we start drawing or building layouts, we make the call if we are going to create a Loud level (combat only), Stealth level (avoid combat), or Mixed style map. For the short period of time given to us, we decided to stick to stealth only. Making this decision early on helped us create better movement options for the player and focus our efforts towards balancing patrols and objective placement. We decided that the theme of the level was a small train depot run by a group of mercenaries shipping large weapons. The main objective was to infiltrate the depot and steal an EMP bomb. Keeping the objective simple and intuitive is important in multiplayer games where players can drop in and out of the experience at any point in time.
We decided to shoot for 10 - 15 minutes of gameplay. Breaking down our main objective into smaller sub-goals that could take about 2 minutes each (this is based on our extensive knowledge of payday 2). It should be noted that this time assessment will change once the player has completed the level a few times. These numbers tend to get cut by a third, or in some cases, by half. With our main objective in mind, we can construct a simple flow diagram for the heist and start to think about possible dynamic and RNG elements that can be used to create a re-playable experience.

(This is a scripting example from our editor, each entity has it's own function)
Testing your ideas before scripting them? Wait... What?
Since 90% of Payday levels are hand scripted, it's important we don't waste time building the wrong things. Testing your objectives and complicated RNG elements has to be fast and efficient. The last thing you want to do is build an entire system and find out it sucks. Most of the time you don't even need animations or even a model to properly test your ideas. At such an early stage some floating debug text will do just fine. You might be asking, what if I don't have debug text or the ability to script? When playtesting levels for Payday 2, a lot of the time we'll get a simple block-out done and then ... here it comes ... pretend we're doing the objectives.
It might sound crazy (and not everyone can get through it without laughing) but we'll have one of the designers act out the role of Bain, our mission giver, and just spout objectives at us. We'll move through the space and pretend to see guards or hack laptops and delay time based on things we expect to happen. You can basically break down how your systems might work and try out a few possibilities. For example, knowing that you might have two escapes at either side of the map gives you enough knowledge to make pretend decisions. Telling your fellow devs the van is arriving up top and pointing out where to secure loot can help you find out if a location is interesting for the escape or not.
Even though the artists might giggle, or people from the other teams walking by stop and wonder why they can't see that hoard of enemies. It really works, and can often steer the level in the right direction and prevent us from investing too much time on the wrong objectives. Now, I know this approach won't work for all studios or situations, but all I gotta say is... don't knock it till you try it...  
   
 
Constructing our Sandbox Layout
Now that we've pretended to run through our objectives and have gotten used to our basic block-out, let's talk about the layout we built for Murky Station. We went for what i'd like to call "the onion approach", which is pretty much what it sounds like. You'll have multi-layered rings that give you the sense of progression towards the center (or a goal). Essentially, we use the outer layer as the player start and each sub-objective is based inside a different layer until the player reaches the main objective (at the figurative center). This approach is very useful when working with sandbox type levels, especially when the player can virtually go anywhere they want.

Side Note: We also layer our music track each time a sub objective is finished, creating more suspense and a sense of agency.

You can see that the outer onion layer is the player spawn (colored green) on the overpass which gives them a full view of the trainyard. From here they can study patrol routes, train-car positions, and possibly objective locations. The overpass can also be used by a player with a sniper rifle to mark guards in the different lanes, helping provide accurate information on guard positions for the players on the ground floor.

The next layer is breaking into the train yard through a fence around the perimeter. The fence is here to guide the player and give them a visual boundary for the "safe zone" (where no guards patrol). The next layer is searching the train cars to discover where the main goal is hiding, followed by breaking through the vault doors inside of the trains themselves. These onion layers have to be carefully managed to give the proper impression to the player. Too many layers and you might confuse the player or make them forget what they're doing, too few and you might leave them feeling unchallenged or unaccomplished.
 
Player Mobility is key!
Mobility is key to providing players opportunities to express themselves and make better decisions while traversing a level. I felt that it was pretty important for Murky Station to allow for different play styles ranging from slow and methodical to fast and dirty. The last thing I wanted was to force players to play a certain way or for the routes to become predictable and linear. In order to do this, I spent the first week of development prototyping and testing out different layout ideas that would maximize paths and choices for the player.
(Here is a simplified top-down of the routes in the train yard area)


It became obvious that we would need to allow players to traverse through and under the trains as they cover most of the real estate in the train-yard. Unfortunately the older train assets were not built to go underneath, but lucky for us, the nighttime setting of the level would cover up this fact. There being only 2 of us on this project, I took a crash course in Maya and cleaned up the bottom half of the trains by removing collisions and remodeling them for readability purposes.


 
The next challenge was to teach the player they could hide under trains and be safe. Payday players haven't been under the trains in any other heist up until this point, so we needed to call attention to that but also show them it was a safe place. Making these spaces dark and in the shadows helped create an illusion of safety but also made it harder for players to find them.
To help solve this issue we added yellow caution tape as a trim and a dim red light under the wheels to catch the players eye. These combined elements would then be used as visual vocabulary in other parts of the level to teach players something should be explored.


One of the other ways we added more routes to the level was to build a ventilation system in the lower tunnels. Leveraging the fact that this was a stealth level to create these smaller spaces, especially since they didn't have to accommodate 40+ police officers. The vents allowed players to safely view guard patrols, search for objectives, and move loot. To prototype this, I built a modular vent system using basic mock-up units that allowed for rapid construction and testing. Funnily enough, the first iteration of the vents was too small and caused players’ bodies to clip through the floor. I was able to rework my mock-up units and we settled on standing height instead of a crouching one. Once again we used yellow caution tape as our visual vocabulary to highlight the vent entrance on the wall.
Modifying the trains and vents is one of the factors that contributed to the map’s success and gave new players more confidence to explore the trainyard and lower claustrophobic tunnels. So now that we've explored the different possibilities for movement and giving the player more choices, it's time to buckle down and get our randomization system built.
 


Randomizing Objectives to Maximize Replayability
RNG is one of the core pillars of Payday, so every decision we make is looked at through a lense of RNG. We strongly believe randomization should be meaningful to gameplay and not just added for the sake of it. It’s important to ask questions like: was it worth changing all the cups in your level? Did you gain anything from swapping out all of your cars and buildings? Was creating a third entrance valuable to the level? Maybe one day we'll completely randomize every object in a building down to the smallest cups, but in a game like Payday I personally feel these types of things have diminishing returns and can often ruin a planned design.
When working with RNG it's important that you ask yourself as many questions as possible to start with a strong foundation, especially if you plan on finishing on time. Something I often see junior to mid-tier level designers forget is to build for scope and set priorities on their objectives. It might sound trivial, but forgetting your priorities can send you down a black-hole that eats away all of your time.
So how did we go about adding RNG into Murky Station? Breaking down our objectives, we can start to consider what RNG options are available and doable within our one month time frame. I've also labeled them with my personal priorities (low - high).
Break into the train yard randomize breach locations (low) Locate the Bomb Train randomize train configurations (high) Hack into the train randomize panel to flip sides (low - medium) Open the Vault 4 different vault door / key types (high) Find the Vault keys The map supported up to 40 hiding locations (med - high) Secure the EMP bomb parts 2 escape locations, 1 chosen per playthrough (medium) I focused most of my efforts on randomizing the train configurations, vault doors and key placement. These objectives were critical in influencing how the player would move through the main space and how they could tackle the same area in different ways through multiple playthroughs. In order to accomplish this, I broke down my sub-goals into digestible points of interest and isolated them into their own prefabs (shown below). Doing so allowed me to script one prefab and teleport it to as many locations as I wanted. This approach made the randomization more manageable to script and cut down the amount of bugs that might have formed if I built everything by hand each time.

Side note: We gave each one of our key / vault prefabs its own unique visual and audio so that players could identify them from a distance or listen if they were close by. Providing them with this level of feedback is critical in helping them make proper decisions while traversing the level.



 
Now that we have our vault doors and keys figured out, I can begin the planning process of placing them throughout the level. When placing them, each location must meet certain conditions before being finalized. The main goal is to provide the player with a challenge and also encourage them to be creative in tackling the surrounding area. Having designed the layout to have many interesting choke points and traversals, it was fairly straightforward where I could place them. Collecting the keys is one of the more RNG based objectives in Murky Station, sometimes all of the keys are in different corners of the map and other times they are all next to each other. Eventually there was a script clean up to prevent overpowered locations or terrible RNG possibilities, but overall it was a huge success for the level.
We generally kept the key locations central to the layout and tried not to place them too close to the player’s safe zones. Placing several keys along the outskirts was a nice change of pace from the main lanes, providing a different type of challenge due to the openness of the layout.
This is what the upper train yard looks like and how the keys are distributed. The lower tunnels have the same amount of keys placed.


 
We also used the same method for spawning the train interiors and vault doors. By creating one prefab and scripting it four times inside the level (one per vault door type) we were able to randomize the location of the players’ main goal with little effort. The engine also allows us to rotate our prefabs, giving us the option to flip the train interiors.  This added a whole new layer to their configurations, since some of the interior layouts were asymmetrical.
We ended up with roughly 600 train configurations, 2000 vault door combinations, and 256 sub objective configurations. With 1 of 2 exits being chosen randomly each playthrough, this really changed what types of decisions got made by the players. It also influenced how they would flow through the level and took advantage of their diverse set of movement options.
On top of that we use non-linear objectives, which basically means you can do multiple objectives at the same time or in some cases, different orders. In Murky Station, players can simultaneously be looking for keys, searching through trains, marking guards from the overpass, and securing extra loot they find. This allows 4 players to comfortably split up to cover more ground and work off each other. A well coordinated team might have two players hacking into the trains to find the EMP bomb, while the others are looking for the vault keys. I find it very important to provide all players an opportunity to contribute towards the main goal.
Side note: With all of this randomization, you might be wondering how QA can test it all. The short answer: they don’t. We need to build efficiently to insure 90% of the level is solid, and then catch as many edge cases as possible. On the Payday team, the frontline of defense for QA is the designer making the level, It’s our job to test our own work thoroughly! The way the systems above were built would only required 1 prefab to be maintained for each example. This provides us the freedom to go nutty with the customization in the level, knowing it has a low chance at affecting our prefabs. So, as long as we build smart we can cut down the amount things QA needs to test and help speed up production.

With the objectives off to a good start, let's take a look at how RNG might affect our guard patrols and cameras in the level.
 

 
Guard Patrols and RNG
Randomization can have a large effect on how smooth or frustrating a level turns out to be. One of the things we have to keep an eye on when designing stealth levels is frustrating the player through poor patrol placement, amount of guards, and how long they pause at each location. The goal is to create a fun puzzle-like challenge, not a terrible waiting game. Bad RNG might have you sitting in a corner for one minute waiting for the guard to leave, only to have another guard take his place when that minute is up. It's our job as the level designer to help prevent such situations from happening by adjusting our timings, reworking the layout, or possibly the level’s mechanics. This is why it's so important to create a solid base for player movement options from the beginning.
Since we don't want our guard patrol RNG to get out of hand, we need to be careful about how they flow through a space. Doing this requires it's own personal attention and multiple iterations. Tilt too far in one direction and you'll end up with bare areas that have no guards, tilt too far in the other direction and you'll have too many guards stacked on each other with no wiggle room. The last thing you want is the possibility of a death chain reaction. This is caused when you kill 1 guard, only to have another guard 10 meters away spot that body... forcing you to kill that guard, who eventually gets spotted by the next, ect. In Payday 2, players have a limit of 4 guards they can kill before the alarm goes off (on all difficulties). In our levels, we have to actively manage the amount of crossover between paths and how often guards might meet.
In the first test pass for Murky Station I ended up with a good amount of coverage for my level, but the downside was that some sections could randomly get 8 guards piled up.  After a bit of playtesting and redesign, I decided to break up my patrols into smaller loops and add more points. This increased the amount of coverage and kept the patrols more consistent. It also lowered the maximum guard stacking to around 4 and drastically reduced the amount of death chain reactions that could happen.

First pass patrol locations

Second pass patrol locations

(the new paths provide the same amount of level coverage with a less chance of guard over-stacking) 
A fresh take on an old mechanic
In most of our stealth levels we use random static security cameras to challenge the players’ skill at avoidance or sabotage. The players have multiple mechanics in order to deal with them in a variety of ways, but we hit a brick wall when discussing options for Murky Station. Due to the hallway nature of the layout and the surrounding structures, we were left with very few options when it came to camera placement. With so few options, the cameras would be no longer modifying the level in a positive way. We also found them at odds with the design of the level, since you were supposed to be searching for a specific train car. If we had cameras pointing at it, you would be able to identify it too quickly and negate the challenge of finding it.

 
So how did we fix these issues? Getting rid of the cameras was not really an option, so we began brainstorming and looking for assets that might be of use. It's important the core camera functionality remain intact and also continue to meet our core pillar of randomization. We discovered an old drone asset for one of the previous levels and began prototyping a few ideas. The design we ended up going with provided us the coverage we needed, while also creating a new challenge for the players to overcome.


 
Each train can spawn up to two drones, which will then fly around the perimeter of the train and scan for players and bodies. Randomly throughout the level, three to four drones will be activated to begin their scan. The loop takes about 30 seconds before they return to their trains and deactivate. The cycle continues like this every few minutes until the level is finished.
On harder difficulties, more drones will spawn and they will become indestructible.
What's great about the drones from a design perspective, is that we can dynamically modify how the level gets played and prevent players from getting comfortable in using the same routes each play-through. Some players will avoid lanes with drones, more skilled players will dodge them using their movement options, and some players might even get trapped and need to think of a new routes. Let's take a look at the patrols and drones in action.
(This clip is sped up about 8x and set to the hardest difficulty to help illustrate pathing and drone movement)
Closing thoughts
Murky Station was such an enjoyable experience to work on that I still play it to this day. When you break down the objectives and how they influence one another in a co-op space, you can begin to see the bigger picture and how a well-planned level with controlled RNG elements can stay fresh and replayable. Experimenting with different types of RNG is something I find very interesting, especially when you combine it with level design. I hope my article gave you some more insight into how we build with RNG and why we consider it one of our core design pillars. If you found this article helpful, let us know in the comment section!
Thanks for reading, here is my Info :
Twitter: @generalvivi 
Email: generalvivi [at] gmail . com
Website: www.generalvivi.com
Before you go!
If you enjoyed this article and would like to hear how we used RNG in other ways, check out Patrick Murphy's article on the Payday 2 level "Hoxton Breakout".
I also have a  speedrun (1min) of the level for you to check out and a playthrough on the hardest difficulty (10 mins) by one of the pros from the community.  
Fastest time 2018 (warning to lower volume)
 
10 min gameplay video showing off a lot of variety in the heist. 
 

(New logo by Yanzl)
I'm sure that by now most of us have our sleeves rolled up and are ready to tackle yet another year, but before we move forward let's take a moment to look back at what 2017 meant for our community. It was a time of immense growth for both professionals and amateurs alike. A time when everyone seemed to have surpassed their former selves. And without slowing down, some have even managed to land their first job in the industry. I don't know what this new year holds, what challenges to overcome will arise, but I know for certain that I'm excited to see everyone become even greater!
 
2017: Mapcore's Year in Review
 

Overwatch - Oasis
by Phillip K, Bram Eulaers, Helder Pinto and others
 

Dishonored 2: Death of the Outsider - Curator level
by electrosheep, kikette and others
 

Payday 2 - Brooklyn Bank level
by General Vivi
 

Sniper Elite 4 - Regilino Viaduct
by Beck Shaw and others
 

Counter-Strike: Global Offensive - Offtime
by Squad
 

Team Fortress 2 - Shoreleave
Art pass, props and sound by Freyja
 

Wolfenstein II: The New Colossus - Farmhouse
Modeled, textured and composed by BJA
 

Half-Life 2: Downfall
by marnamai
 

Counter-Strike: Global Offensive - Studio
by ZelZStorm, TanookiSuit3 and Hollandje
 

Portal 2 - Refraction
by Stract
 

Counter Strike: Global Offensive - Breach
by Yanzl and Puddy
 

Counter-Strike: Global Offensive - Berth
by grapen
 

Counter-Strike: Global Offensive - Kaizen
by Andre Valera and Jakuza
 

Counter-Strike: Global Offensive - Asylum
by Libertines
 

Half-Life 2: Episode 2 - FusionVille: The Shadow over Ravensmouth
by Klems
 

Unreal Engine 4 scene
by Dario Pinto
 

Counter-Strike: Global Offensive - Grind
by The Horse Strangler, `RZL and MaanMan
 

Counter-Strike: Global Offensive - Aurelia remake
by Serialmapper
 

Counter-Strike: Global Offensive - Tangerine
by Harry Poster
 

Counter-Strike: Global Offensive - Abbey
by Lizard and TheWhaleMan
 

Counter-Strike: Global Offensive - Apollo
by Vaya, CrTech, Vorontsov, JSadones
 

Counter-Strike: Global Offensive - Sirius
by El Exodus
 

Unreal Engine 4 scene
by Corvus
 

Counter-Strike: Global Offensive - Subzero
by FMPONE
 

Counter-Strike: Global Offensive - Biome
by jd40

This is the second part of a technical analysis about Source Lighting, if you haven’t read the first part yet, you can find it here. 
Last time, we studied the lightmaps, how they are baked and how VRAD handles the light travel through space. We ended the part 1 with an explanation of what the Constant-Linear-Quadratic Falloff system is, with a website that allows you to play with these variables and see how lighting falloff reacts to them. We will now continue with basic examples of things you can do with these variables. 
 
Examples of application
Constant falloff
The simplest type of falloff is the 100% constant one. Whatever the distance is, the lighting has theoretically the same intensity. This is the kind of (non-)falloff used for the sun lighting, it is so far away from the map area, that light rays are supposed to be parallel and light keep its intensity. Constant falloff is also useful for fake lights, lights with a very low brightness but that are here to brighten up the area.
 
 

 
Linear falloff

Another type of falloff is the 100% linear one. With this configuration, light seems to be a bit artificial: it loses its intensity but goes way further than the 100% quadratic falloff. It can be very useful on spots, the lighting is smooth and powerful. Here is an example:
 

 
Quadratic falloff

This is the default configuration for any light entity in Hammer, following as we said before the classic Inverse-Square law (100% Quadratic Falloff). It is considered to be the most natural and realistic falloff configuration. The biggest issue is that it boosts the brightness so much on short distances, that you can easily obtain a big white spot. Here is an example, with a light distant of 16 units from a grey wall:

 
This can also happen with linear falloff but it is worse with quadratic. Simple solutions exist for that, the most common is not to use a light entity but a light_spot entity that is oriented to the opposite direction from the wall/ceiling the light is fixed to. You can make the opening angle of your light_spot wider, with the inner and outer angle parameters (by default the outer one is 45°, increase that to a value of 85° for example). If needed, you can also add a light with low brightness to light the ceiling/wall a bit.

 
50% & 0% FallOff
A second light falloff system exists, overriding the constant-linear-quadratic system if used. The concept is much simpler, you have to configure only 2 distances:
50 percent falloff distance: Distance at which light should fall off to 50% from its original intensity 0 percent fall off distance: Distance at which light should end. Well ... almost, it actually fall off to 1/256% from its original intensity, which is negligible. The good thing with this falloff system is that you can see the 2 spheres according to the 2 distances you have configured in Hammer. Just make sure to have this option activated: 

 
Models lighting
An appropriate section for models lighting is needed, because it differs from brush lighting (but the falloff stays the same). In any current game engine, lightmaps can be used on models, a specific UV unwrap is even made specifically for lightmaps. But on Source Engine 1 (except for Team Fortress 2) you cannot use lightmaps on models. 
The standard lighting method for models is named Per-Vertex Lighting. This time, light won’t be lighting faces but vertices, all of the model’s vertices. For each one of them, VRAD will compute a color and brightness to apply. Finally, Source Engine will make a gradient between the vertices, for each triangle. For example:

If we take a simple example of a sphere mesh with 2 different light entities next to it, we can see it working.
            
With this lighting method, models will therefore be integrated in the environment with an appropriate lighting. The good thing is that, if a part of the model is in a dark area, and another part is in a bright area, the situation will be handled properly. The only requirement for this is that the mesh must have a sufficient level of detail in it; if there is a big plane area without additional vertices on it, the lighting details could be insufficient. 
Here is an example of a simple square mesh with few triangles on the left and a lot on the right. With the complex mesh, the lighting is better, but more expensive. 

If you need a complex mesh for your lighting, you don’t want your model to be too expensive, you have to find a balance. 
Two VRAD commands are needed to make the Per-Vertex Lighting work:
StaticPropLighting StaticPropPolys You have to add them here. You can find more information here.
Another system exists, that is much cheaper and simpler. Instead of focusing on the lighting of all the vertices, the engine will only deal with the model’s origin. The result obtained in-game will be displayed on the whole model, using only what has been computed at the model’s origin location. This can be an issue if the model is big or supposed to be present in an area with lots of contrast in lighting. The best example for that is at the beginning of Half-Life 2 with trains entering and exiting tunnels. We can see the issue: the model is illuminated at the beginning, but when it enters the tunnel it suddenly turns dark. And this moment is when the train’s origin gets in the shadow. 
This cheap lighting method will replace the per-vertex lighting for 3 types of models:
For prop_dynamic or any kind of dynamic models used in the game (NPCs, weapon models in hand, any animated models...) For prop_physics For ANY MODEL USING A NORMAL MAP (vertex lighting causes issues with normal maps apparently), EVEN IF USED AS A PROP_STATIC
The big problem with these models is their integration in the map, they won’t show any shadow and their lighting will be very flat and boring (because it’s the same used for the whole model). But hopefully there are 2 good things with this cheap lighting method. 
First, the orientation from which comes light is taken into account, if blue light comes from one direction, therefore all the faces oriented toward this direction will be colored in blue. And if you have different lighting colorations/intensities coming from different sides of your model, they should appear in game. 
Here is an example of a train model using a normal map with 2 lights on both side. If you look closely, you’ll see some blue lighting on the left, on faces that are supposed to be in the shadow of the blue light but are oriented toward the blue light.
 

 
The second good thing is that there is still some kind of dynamic per-vertex lighting, but much simpler: it only works with light and light_spot entities (NOT with light_environment), and it just adds some light to the prop, it cannot cast any shadow (it only takes into account dynamically the distance between the light and the vertex). If we use again the high-poly plane mesh we had before as a prop_dynamic, being parented to a func_rotating that ... rotates. Light is dynamically lighting the vertices of the props. There is a limit of 3 dynamic lights per prop, it can’t handle more at the same time.

And if you add a normal-map in your model’s texture, this cheap dynamic lighting works on it:

 
Projected texture and Cascaded Shadows
Few words to finish the study with dynamic lighting. Projected textures is a technology that appeared with Half-Life 2: Episode Two in 2007, it consists of a point-entity projecting a texture in the chosen direction, with a chosen opening angle (fov). The texture is projected with emissive properties (it can only increase the brightness, not lowering it) and it can generate shadows or not. The great thing with this technology is that it’s fully dynamic, the env_projectedtexture can move and/or aim at moving targets. This technology is used for example on flashlights in Source games. But as usual, there is also a drawback: most of the time you can only use only 1 projected texture at a time, modders can change this value quite easily but on Valve games it is always locked on 1. 

The cascaded shadows system is only used on CS:GO. The concept is quite similar from a projected texture but it doesn’t increase the brightness, it only adds finer shadows. It is used for environment lighting, using much smaller luxels than for the lightmaps and it is fully dynamic. It starts from the tools/toolsskybox textures of the map and cast shadows if it meets any obstacle. Shadows from the lightmap are most of the time low resolution and the transition between a bright and a dark area is blurry and wide. Therefore, the cascaded shadow will be able to draw a clear shadow around the one from the lightmaps.

When an object is too small to get a shadow in the lightmap, it will be visible thanks to the cascaded shadows. There are 3 levels of detail for cascaded shadows on Counter-Strike, you can configure the max distance at which the cascaded shadows will work in the env_cascade_light entity at the parameter Max Shadow Distance (by default it’s 400 units). The levels of detail will be distributed within this range, for example: 

Since cascaded shadows and projected textures share some technology, you can’t use them both at the same time.
 
Conclusion
I really hope you have found this article interesting and learned at least few things from it. I believe most of these informations are not the easiest to find and it’s always good to know how your tools work, to understand their behavior. Source Engine 1 is old and its technologies might not be used anymore in the future, more powerful and credible technologies are released frequently but it’s always good to know your classics, right? 
I would like to thank Thrik and ’RZL for supporting me to write this article, and long live the Core!
// Written by Sylvain "Leplubodeslapin" Menguy
Additional commands for fun
Mat_luxels 1                              // Allows you to see the lightmaps grids Mat_fullbright 1                         // Disables all the lighting (= fullbright). On CS:GO, cascaded shadows stay and you should delete them as well (cf next command) Ent_fire env_cascade_light kill  // KILL WITH FIRE the cascade shadows entity Mat_drawgray 1                        // Replace all the textures with a monochrome grey texture, useful to work on your lighting  Mat_fullbright 2                         // Alternative to Mat_drawgray 1 Bonus:
Mat_showlowresimage 1           // Minecraft mode

After the announcement of the Reddit + Mapcore mapping contest, the website has welcomed many newcomers. A proof that, even if it is a twelve year old game engine, Source engine attracts map makers, and there are lots of reasons for that. It is common knowledge that technology has moved forward since 2003, and many new game engines have found various techniques and methods to improve their renderings, making the Source Engine older and older. Nevertheless, it still has its very specific visual aspect that makes it appealing. The lighting system in Source is most definitely one of the key aspects to that, and at the end of this article you will know why.
 
About the reality...
Light in the real world is still a subject with a lot of pending questions, we do not know exactly what it is, but we have a good idea of how it behaves. The most common physic model of light element is the photon, symbolized as a single-point particle moving in space. The more photons there are, the more powerful light is. But light is in the same time a wave, depending on the wavelengths light can have all kind of color properties (monochrome or combined colors). Light travels through space without especially needing matter to travel (the space is the best example; even without matter the sun can still light the earth). And when it encounters matter, different kind of things can happen:
Light can bounce and continue its travel to another direction Light can be absorbed by the matter (and the energy can be transformed to heat) Light can go through the matter, for example with air or water, some properties might change but it goes through it And all these things can be combined or happen individually. If you can see any object outside, it is only because a massive amount of photons traveled into space, through the earth’s atmosphere, bounced on all the surfaces of the object you are looking at, and finally came into your eyes.
How can such a complex physical behavior from nature be simulated and integrated into virtual 3D renderings?
One of the oldest method is still used today because of its accuracy: the ray-tracing method. Just to be clear, it is NOT used in game engines because it is incredibly expensive, but I believe it is important to know how and why it has been made the way it is, since it probably influenced the way lighting is handled in Source and most videogame engines. Instead of simulating enormous amount of photons traveling from the lights to the eye/camera, it does the exact opposite. If you want a picture with a 1000x1000 resolution, you will only need to simulate the travel of 1 000 000 photons (or “rays”), 1 for each pixel. Each ray is calculated individually until it reaches the light origins, and at the end the result is 1 pixel color integrated in the full picture. 
By using the laws of physics we discovered centuries ago, we can obtain a physically-accurate rendering that looks incredibly realistic. This method is used almost everywhere, from architectural renderings to movies. As an example, you can watch The Third & The Seventh by Alex Roman, one of the most famous CGI videos of all time. And because it is an efficient way to render 3D virtual elements with great lighting, it will influence other methods, such as the lightmap baking method.
 
Lightmap baking
OKAY LET’S FINALLY TALK ABOUT THE SOURCE ENGINE, ALRIGHT!
A “lightmap” is a grid that is added on every single brush face you have on your map. The squares defined by the grid are called Luxels (they are kind of “lighting pixels”). Each luxel get its 2 own properties: a color and a brightness. You can see the lightmap grids in hammer by switching your 3D preview to 3D lightmap grid mode.

You can also see them in-game with the console command mat_luxels 1 (without and with).
During the compilation process, a program named VRAD.exe is used. Its role is to find the color and brightness to apply for every single luxel in your map. Light starts from the light entities and from the sky (from the tools/toolsskybox texture actually, using the parameter values that has been filled in the light_environment entity), travels through space and when it meets a brush face:
It is partially absorbed in the lightmap grid A less bright ray bounces from the face Here is an animated picture to show how a lightmap grid can be filled with a single light entity:

When you compile your map, at first the lightmaps are all full black, but progressively VRAD will compute the lightmaps with all the light entities (one by one) and combine them all at the end. Finally, the lightmaps obtained are applied to the corresponding brush faces, as an additive layer to the texture used on that face. Let us take a look at a wall texture for example.

On the left, you have the texture as you can see it in hammer. When you compile your map, it generates the lightmaps and at the end you obtain the result on the right in-game. Unfortunately, luxels are much rougher, with a lower resolution, more like this.

On the left you have a lightmap grid with the default luxel size of 16 units generated my VRAD, a blur filter is applied and you obtain something close to the result on the right in the game.
In case you did not know, you can change the lightmap grid scale with the “Lightmap Scale” value with the texture tool. It is better to use values that are squares of 2, such as 16, 8, 4 or even 2. Do not go below 2, it might cause issues (with decals for example). Only use lower values than the default 16 if you think it's really useful, because you will drastically increase your map file size and compilation time with precise lightmap grids. Of course, you can also use greater values in order to optimize your map, with values such as 32, 64 or even 128 on very flat areas or surfaces that are far away from the playable areas. You can get more infos about lightmaps on Valve’s Wiki page.

But as we said before, light also bounces from the surface until it meets another brush, using radiosity algorithms. Because of that, even if a room does not have any light entity in it, rays can bounce on the floor and light the walls/ceiling, therefore it is not full black. 
Here’s an example:

The maximum amount of bounces can be fixed with the VRAD command -bounce X (with X being the maximum amount of bounces allowed). The 100 default value should be more than enough.
Another thing taken into account by VRAD is the normal direction of each luxel: if the light comes directly against the luxel or brushes against it, it will not behave in the same way. This is what we call the angle of incidence of light.

Let us take the example of a light_spot lighting a cylinder, the light will bright gradually the surface - from fully bright at the bottom to slightly visible at the top.

In-hammer view on the left, in-game view on the right
 
Light Falloff laws
One of the things that made the Source Engine lighting much more realistic than any others in 2004 is the light falloff system. Alright, we saw that light can travel through space until it meets something, but how does it travel through space? At the same brightness, whatever the distance is between the light origin and destination? Maybe sometimes yes… but most of the time no.

 
Imagine a simple situation of a room with 1 single point light inside. The light is turned on, it produces photons that are going in all the directions around it. As you might imagine, photons are all going in their own direction and have absolutely no reason to deviate from their trajectory.
 
 
 
At one time, let’s picture billions of photons going in all the directions possible around the light, the moment after, they are all a bit further in their own trajectory, and all the photons are still there, in this “wave”. But, as each photon follows its own trajectory, they will all spread apart, making the photon density lower and lower.
As we said before, the more photons there are, the more powerful light is. And the highest the density, the more intense light is. Intensity of light can be expressed like this:

 
You have to keep in mind that all of this happens in 3D, therefore the “waves” of photons aren’t circles but spheres. And the area of a sphere is its surface, expressed like this:

(R is the radius of the sphere)
 
If we integrate that surface area in the previous equation:

With ♥ being a constant number. We can see the Intensity is therefore proportional to the reverse of the square of the distance between the photons and their light origin. 
So, the further light travels, the lower is its intensity. And the falloff is proportional to the inverse of the square of the distance.
Consequently, the corners of our room will get darker, because they are farther away from the light (plus they don’t directly face the light, the angle of incidence is lower than the walls/floor/ceiling).

This is what we call the Inverse-Square law, it’s a very well-known behavior of the light in the field of photography and cinema. People have to deal with it to make sure to get the best exposure they can get.
This law is true when light spreads in all possible directions, but you can also focus light in one direction and reduce the spread, with lenses for example. This is why, when Valve decided to integrate a lighting falloff law in their engine, they decided to use a method not only following the inverse-square law but also giving to mapmakers the opportunity to alter the law for each light entity.
 
Constant, Linear, Quadratic... Wait, what?
In math, there is a very frequent type of functions, named polynomial functions. The concept is simple, it’s a sum of several terms, like this:

Every time, there is a constant factor (the “a” thing, a0 being the first one, a1 the second one, a2 the third one...), multiplied with the variable x at a certain degree:
x^0 = 1 : degree 0 x^1 = x : degree 1 x^2 : degree 2 x^3 : degree 3 ... And
a0 is the constant named “constant coefficient” (associated to degree 0) a1 is the constant named “linear coefficient” (associated to degree 1) a2 is the constant named “quadratic coefficient” (associated to degree 2) Usually, the function has an end, and we call it by the highest degree of x it uses. For example, a “polynomial of the second degree” is written:

Then, if we take the expression from the inverse-square law, which was:

With a2 = 1 and D being the variable of distance from the light origin.
In Source, the constant ♥ is actually the brightness (the value you configure here).
It is simply an inverse polynomial of the second degree, with a0 and a1 equal to zero. And we could write it like this:

Or...

And here you have it! This is approximately the equation used by VRAD to determine the intensity of light for each luxel during the compilation. And you can alter it by changing the values of the 3 variables constant, linear and quadratic, for any of your light / light_spot entity in your level.
Actually you set proportions of each variable against the other two, and only a percentage for each variable is saved. For example:

Another example:

By default, constant and linear are set to 0 and quadratic to 1, which means a 100%quadratic lighting attenuation. Therefore, by default lights in Source Engine follows the classic Inverse-Square law.
If you look at the page dedicated to the constant-linear-quadratic falloff system on Valve’s Wiki, it’s explained that the intensity of light is boosted by 100 for the linear part of equation and 10 000 for the quadratic part of equation. This is due to the fact that inverse formulas in equations always drop drastically at the beginning, and therefore a light with a brightness of 200 would only be efficient in a distance of 5 units and therefore completely pointless.

You would have to boost your brightness a lot in hammer to make the light visible, that's what Valve decided to make automatically.
The following equation is a personal guess of what could be the one used by VRAD:

With constant, linear and quadratic being percentage values. The blue part is here to determine the brightness to apply, allowing to boost the value set in hammer if it is as least partially using linear or quadratic falloff. The orange part is the falloff part of equation, making the brightness attenuation depending of the distance the point studied is from the light origin. 
The best way to see how this equation works is to visualize it in a 2D graph: 
https://www.desmos.com/calculator/1oboly7cl0
This website provides a great way to see 2D graphics associated to functions. On the left, you can find all the elements needed with at first the inputs (in a folder named “INPUTS”), which are:
a0 is the Constant coefficient that you enter in hammer  a1 is the Linear coefficient a2 is the Quadratic coefficient B is the Brightness coefficient In another folder are the 3 coefficients constant, linear and quadratic, automatically transformed into a percentage form. And finally, the function I(D) is the Intensity function depending on the distance D. The drawing of the function is visible in the rest of the webpage. 
Try to interact with it!
This concludes the first part, the second part will come in about two weeks. We will see some examples of application of this Constant-Linear-Quadratic Falloff system, and a simpler alternative. We will also see how lighting works on models and dynamic lighting systems integrated in source games.Thank you for reading!
 
Part Two : link