Diesel-X is a game meant to test various listening comprehension parameters related to a study in dyslexia. These include frequenty modulation discrimination threshold, letter knowledge and phoneme recognition. At the time of the original study, a few design proposals were laid out, the final proposal was one where a genius child works with her robot dog, Diesel-X (a pun based on the words dyslexia and diesel engine). She is tasked with saving the city from cats who are terrorizing the population, by undertaking several different tasks. For example Alex must pick out cats that are hiding stolen gold with a metal-detector sound that incorporates the frequency modulation. In another task, Alex must pick out the culprit cat from a line up where they are holding letter signs, to test knowledge of letters.
The game itself enjoys simple design, but was originally made with Unity 3. Upgrading to the 2018 version meant a lot of refurbishing, updating and mountains of bugfixes.
One particular incident is worth mentioning on its own. Diesel-X allows you to change the color pattern of Diesel as a reward between tasks. The colors have 10 different options, applied to 3 sections of Diesel's body; the head, torso and legs. In the original version, this was implemented using a seperate texture for each possible color combination. That means there were 10 to the power 3 or 1000 seperate textures named as 'HEAD_BLACK_TORSO_BLACK_LEGS_BLACK.png', 'HEAD_BLACK_TORSO_BLACK_LEGS_BLUE.png' etc. These textures on their own took up about a gigabyte of space in the final apx, as opposed to the rest of the game being around 200MB. This system was immediately improved by splitting Diesel's UV layout in 3 materials, each with 1 color value, removing 999 redundant textures.