Chapter 11 Mixed-initiative content creation

Algorithms can generate game content, but so can humans. And while PCG algorithms can generate some kinds of game content remarkably well and extremely quickly, some other types (and aspects) of game content are still best made by humans. Can we combine the advantages of procedural generation and human creation somehow? This chapter discusses mixed-initiative systems for PCG, where both humans and software have agency and co-create content. A small taxonomy is presented of different ways in which humans and algorithms can collaborate, and then three mixed-initiative PCG systems are discussed in some detail: Tanagra, Sentient Sketchbook, and Ropossum. 11.1 Taking a step back from automation Many PCG methods discussed so far in this book have focused on fully automated content generation. Mixed-initiative procedural content generation covers a broad range of generators, algorithms, and tools which share one common trait: they require human input in order to be of any use. While most generators require some initial setup, whether it’s as little as a human pressing “generate”, or providing configuration and constraints on the output, mixed-initiative PCG automates only part of the process, requiring significantly more human input during the generation process than other forms of PCG. As the phrase suggests, both a human creator and a computational creator “take the initiative” in mixed-initiative PCG systems. However, there is a sliding scale on the type and impact of each of these creators’ initiative. For instance, one can argue that a human novelist using a text editor on their computer is a mixed-initiative process, with the human user providing most of the initiative but the text editor facilitating their process (spell-checking, word counting or choosing when to end a line). At the other extreme, the map generator in Civilization V (Firaxis 2014) is a mixed-initiative process, since the user provides a number of desired properties of