• Orcun Nisli

Difficulty Curves in Endless Runners

Updated: Apr 8, 2018

Procedural Map Generation with Minorly Varying Constant Map Parts

Procedural level design does not mean that these levels should be randomly ordered. For endless runner games, pattern recognition has a big role. Player learns how to recognize the action patterns and how to operate the moves to complete these patterns. Most of game design failures in this genre is related to the lack of pattern recognition consistency, or to the lack of minor variations.

The best example in this regard is without doubt the two layered procedural design of Subway Surfers. The visual layout outside of the actual game field is ordered in a different layer. This visual layer merge with the game field layer in bonus parts hidden in upper installations and through the tunnels that sometimes connect different game-field subsections. These subsections offer a quickly recognized game experience while preventing repetitiveness via small variations.

Did you know that? In Subway Surfers, in order to avoid overloading of physics engine, the trains that move towards the player place their bounding box statically at the point of contact, depending on the game’s speed at that instant. Therefore, even if they move visually, theoretically, they constitute static obstacles like other obstacles in the game.

The balance between the randomness and pattern recognition should be carefully/masterfully built/crafted in our project. Within “Buddies: Dash In Time”, there are several stages that are divided in parts such as Farms, City, Fortress, Arena, Market Places etc. Each of these parts are composed of 6-8 subsections that can also contain minor variations. The player, in order to pass to the next stage, should traverse through 16-32 subsections: this means that each subsection repeats 2 or 3 times during the game. Each stage aims to be memorised(?) by specific visual aesthetics and color coding. During the first sessions, the player will experience only two of these stages. Other stages will be unlocked sequentially once the player completes missions and levels up. This sequential progression is important in building a joyful ride for the beginners, and bringing new challenges to more advanced players, and thus, completing an easy-to-learn-hard-to-master game design.

Another factor that should be taken in consideration for procedurally generated stages is to design them with a speed-proof approach. Because they will be ordered in a random fashion, each stage should offer experiences conforming to the minimum, average and maximum game speed with an increasing, but not impossible level of difficulty.

Difficulty Curve for Jumping

Changing the difficulty of procedurally generated maps with minor variants is critically important.

Beyond classical reflex timing challenges, which is common for all endless runners, Subway Surfers have a very significant success in creatively managing the difficulty curves with “Air Control Mastery”. The game tutorial does not reveal that there is a chance of air control (runner instantly dive to ground if the player swipe down while on air) and none of the obstacles is designed to require that skill during the low speed runs. After a while, run speed increases to a specific range and few obstacle designs (which are already used regularly on low speeds) begin to require the air control skill to be discovered for longer runs. At the maximum speed, the air control becomes an important part of the game, which is used almost in each second of the run, and player need to master this action to survive. This excellent trick converts the gameplay to an easy-to-learn-hard-to-master experience, which can be taken as example for our project.

The secret paths that will be used in “Buddies: Dash In Time” are good instances where the experience of air control mastery can be used and be expanded.

By using the catapults in the game, the player can make longer and higher jumps (that can be continued only in the middle lane). This allows to win bonus gold during the fly and a power-up at the end. To connect two stages, we use the same catapult. Catapult throws protagonist over the castle walls and continue the run over there. During the long-jump experience, the camera targets a higher point of normal view in order to reveal the target location better, and when the protagonist hits the peak, it starts to focus down in order to show the ground, and therefore, to let the player avoid any obstacle that might be on the track that is about to be landed on. During the first part of this jump-journey where the main focus is to collect gold coins, the player does not perceive what is left down the road: it is rather a lucrative and calm ascent. The secret path design above was built to be discovered at this very moment when a player chooses to descend from the jump.

What do you think? Would that work?

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