FlexStroke is a research project while I was interning in Microsoft Research Asia with Jiawei Gu in HCI group.


FlexStroke is a new system to enhance the tactile experience of digital painting hat includes multi-strokes for different painting needs. It values craft process of digital painting, including haptic feedback and customized strokes with different visual effects. Based on jamming structure, the tip of our stylus has changeable stiffness.

Jamming is a mechanism by which body can transfer between deformable and stiff states with very small change in its volume. Jamming can be experienced in vacuum-packed coffee grounds. When particles are in a loosely packed state, the whole package is soft and deformable; when air is removed, particles are jammed into a rigid state.

When the tip is soft, users can deform it. For a fixed shape, a vacuum pump controls its stiffness and the tip turns solid-like. Visual simulations on PixelSense from Microsoft jointly enhance the intuitive painting process with realistic display results.


In a recent prototype, we demonstrated three different tip patterns: a Chinese brush (soft and deformable), an oil brush (customized flat shapes), and a crayon (fixed strokes). They differ in terms of tip stiffness and visual effects. In addition, the oil brush and crayon can physically change color with LEDs.

The digital canvas and software system is based on Microsoft’s PixelSense. Its IR sensing system provides access to raw image data of the tip contact area on the screen.


Liu, Xin, Haijun Xia, and Jiawei Gu. “FlexStroke: a jamming brush tip simulating multiple painting tools on digital platform.” UIST 2013, Demo

Liu, Xin, and Jiawei Gu. “FlexStroke: a flexible, deformable brush-tip with dynamic stiffness for digital input.” TEI 2014