A design engine for designing an article to be worn on a human body part (input canvas) in a virtual environment. A virtual model engine of the design engine is used to generate and modify a virtual model of the input canvas and a virtual model of the article based on skin-based gesture inputs detected by an input processing engine. The gesture inputs comprise contacts between an input tool and the input canvas at locations on the input canvas. The virtual model engine may implement different design modes for receiving and processing gesture inputs for designing the article, including direct manipulation, generative manipulation, and parametric manipulation modes. In all three modes, a resulting virtual model of the article is based on physical geometries of at least part of the input canvas. The resulting virtual model of the article is exportable to a fabrication device for physical fabrication of the article.