In a recent blog post, Paavo Huhtala, a Finnish developer, delved into the intricacies of the rendering pipeline in Cities - Skylines 2, offering valuable insights into the performance woes of this newly released city-building game. His comprehensive analysis, primarily conducted using the graphics debugger Renderdoc, uncovered a series of technical glitches that place an undue burden on the graphics card.

At the heart of the problem lies Unity's engine feature, Data-Oriented Technology Stack (DOTS), which is responsible for efficiently distributing processing loads across multiple CPU cores. However, in Skylines 2, the game faced limitations with this feature, prompting developers to create specific technical systems to bridge the gap between DOTS and the regular Unity render system.

The trouble with these bespoke features is that some of them remain unfinished, resulting in rendering unnecessary details or incorrectly handling the level of detail (LOD). For instance, the shadow system accounts for a staggering 40ms of the render time due to unnecessary drawcalls, irrespective of an object's visibility or distance. This issue extends to other aspects of the game, with overly detailed rendering of certain game objects, such as invisible teeth on characters, needlessly taxing the graphics card.

These technical shortcomings, combined, explain the game's unusually high demand for performance. Importantly, Huhtala does not attribute these issues to developer incompetence but rather to challenges arising from the selection of engine features that turned out to be less advanced or integrable than initially assumed, coupled with time constraints for completing in-house solutions.

It's worth noting that this analysis was conducted based on patch version 1.0.11f1. Although patch 1.0.12f1 has been released subsequently, it provides only partial solutions to the identified problems, leaving some of the issues unresolved.