Refining with Puzzle Dependency Charts

February 23, 2018

Recently I’ve blogged about refining various aspects of the design for the upcoming Sleuthhounds Cruise game using the layout of the game world as well as physical props. Continuing with this trend, this time I’m discussing another tool: puzzle dependency charts.

I first learned about puzzle dependency charts from the blog of Ron Gilbert, of The Secret of Monkey Island fame. They’re a design and planning tool used to work out what puzzles a player encounters in an adventure game and when. A simple example has a player confronted with a locked door. Opening the door, once it’s unlocked, would be a node in the chart. The previous node would be unlocking the door with the key. The previous node to that would be getting the key from wherever it is in the game environment. In this way the steps for proceeding through the game are laid out.

One useful aspect of puzzle dependency charts is that they visually show how linear or non-linear the game is. The more branches of the chart that the player can go down at any given time, the more non-linear. Here’s an excerpt from the puzzle dependency chart for Act 1 of the Cruise game:

[The start of Homes's journey in the new game.]
The start of Homes’s journey in the new game.

Don’t bother trying to read the text in the different node boxes. I took the precaution of randomizing each of the letters so as to not spoil any of the game’s actual puzzle solutions.

Act 1 of the game starts with Pureluck Homes and Jane Ampson working independently from one another as they’ve not yet met. This excerpt from the chart is for the start of playing as Pureluck Homes. This beginning is represented by node 1 in the chart. We can see that from this node there are four lines branching off. Homes starts at a crime scene and he has four different areas of that crime scene that he can immediately investigate and do something in. This provides a degree of non-linearity to the game and gives players the choice of how they want to proceed.

We can also see from the extract that node 5 is connected to both node 2 and node 3. This indicates that the player must complete both node 2 and node 3 before they have what they need to complete node 5. The player is free to do 2 and 3 in either order, but both must be completed in order to proceed.

We can also see a more linear path along the bottom of the excerpt. Here the player must complete node 4 before completing node 6 and before completing whatever node 6 connects to.

[The current structure of Act 1.]
The current structure of Act 1.

Taking a broader view, the above thumbnail diagram shows what the puzzle dependency chart looks like for the entirety of Act 1 so far. Something that should be immediately apparent is the presence of two different types of nodes. Blue nodes represent steps that only Pureluck Homes can do. Purple nodes represent steps that only Jane Ampson can do. With the characters working separately during Act 1, the game itself will determine when to switch between the characters. Later on in the game the player will be able to choose when to switch between Homes and Ampson.

We can see from the thumbnail that the game starts with a fairly non-linear section of puzzles for Homes before moving into a linear stretch that alternates between Homes and Ampson. This then moves into a non-linear section of puzzles for Ampson before heading towards the linear resolution of Act 1.

It should be noted that this is the current chart for Act 1. A number of the puzzles in the chart, especially during the linear sections, I intend to break out to be more non-linear. Having a degree of non-linearity in gameplay is useful because if a player gets stuck on a puzzle in one branch of the chart they can go work on a puzzle in a parallel branch of the chart until inspiration strikes. At the same time, a game shouldn’t be too non-linear because then the player is presented with more options than they can comprehend. A player can’t solve a puzzle if they don’t even know where to begin.

When working on puzzle dependency charts I find it very useful to think backwards through the game. Going back to our initial example of a locked door that the player has to get through, the thinking goes exactly as I described. First, I’ll add a node for opening the door. That’s not much of a puzzle but it’s a place to start in the design. From there it becomes possible to work backwards to figure out what it is that stops the player from opening the door. From the example, perhaps they have to find a key. Grabbing a key and unlocking a door still isn’t very interesting so maybe the next step backwards is that the key is broken and the player has to use a furnace/forge to repair the key. Going backwards from there, we’d probably have non-linear steps for finding each of the key pieces. We may also have another non-linear step for stoking the furnace. In this way we can start to build up more interesting and layered puzzles. That’s where being able to see the non-linearity on the chart is really useful.

For previous Sleuthhounds game I’ve gotten by using Microsoft PowerPoint to create the puzzle dependency charts. Using PowerPoint’s flow chart symbols I was able to create boxes and lines to represent the different puzzle steps. I could even colour the boxes differently to represent Homes and Ampson. However, PowerPoint isn’t a design tool and it has some significant drawbacks when it comes to creating puzzle dependency charts.

As I’ve described, when I’m working on puzzles I tend to start with the final obstacle and then work back through the steps the player must do to overcome that final obstacle. This approach requires I put the final obstacle node in and then insert additional nodes before the obstacle to represent each step. In PowerPoint this requires a lot of manual dragging around of node boxes and lines in order to make room for the inserted nodes. Time spent on formatting the puzzle dependency chart in this way is time not spent on actually figuring out the puzzles for the game.

The previous Sleuthhounds games have all been relatively small. As such I was able to suffer through using PowerPoint to build their puzzle dependency charts. However, for the Sleuthhounds Cruise game, being much bigger and more complex, it was going to be really painful to use PowerPoint to do the design. Consequently, I took a day to put together a puzzle dependency chart application for my own use. The application takes care of spacing out the chart automatically as new nodes are inserted.

As I described, the charts show steps that Homes can perform in blue and ones that Ampson can perform in purple. The application allows these to be quickly chosen from a small colour palette at the bottom of each node. It also allows for the selection of a grey colour, which represents steps that can be done by either Homes or Ampson, which becomes a possibility later in the game when the player can control switching between the characters. The application also displays counts of how many nodes exist for each colour, which is useful to ensure that the game’s puzzles aren’t biased towards one character over the other.

As should be apparent by now, for Sleuthhounds Cruise there’s no one tool I’m using to design it. In fact, I’ve still got a couple more to blog about over the coming weeks. So be sure to check back for more game design notes in the future.