Abstract: Most present-day interactive paint applications lack the means of adequately capturing a user's gestures and translating them into realistic and predictable strokes, despite the importance of such a mechanism. We present a novel brush design that adopts constrained energy optimization to deform the brush tuft according to the user's input movement. It incorporates bidirectional paint transfer and an anisotropic friction model. The main advantage of our method is its ability to handle a wide range of brush tuft shapes that are animated using a freeform deformation lattice, which is associated with the tuft's geometry. This way, almost no conditions or limitations are placed upon the appearance of the brush. Examples range from round brushes modeled as polygon meshes, to flat brushes with individual bristles. Less common deformable tools that are used to apply or remove paint on the canvas, like sponges, can be created as well. The model is integrated in our interactive painting system for creating images with watery paint.