1. A method for simulating painting on a digital canvas, comprising: depositing a plurality of polygons on the digital canvas, the polygons representing pigment deposited on the digital canvas, a boundary of each deposited polygon defined by a plurality of vertices, and each deposited polygon corresponding to one or more wetness values that initially indicate that the polygon is wet; depositing one or more water polygons on the digital canvas, the one or more water polygons representing wetness deposited on the canvas; rasterizing the water polygons into a wetness layer, each point in the wetness layer including a wetness layer value that indicates wetness at the respective point, the one or more wetness values corresponding to the water polygons being indicated by the wetness layer values in corresponding regions of the wetness layer; iteratively performing: growing the boundary of at least one wet polygon by moving at least one vertex of the respective polygon according to a local vector at the vertex and a velocity at the vertex; rendering at least one of the grown polygons to the digital canvas; and aging at least one of the deposited polygons by decrementing at least one wetness value corresponding to the respective polygon based at least in part on the wetness layer; until all of the polygons are dry according to the corresponding wetness values; and, during at least one iteration, resampling the boundary of each wet polygon to redistribute the vertices prior to said growing the boundary, after said resampling the vertices being distributed on the boundary so that the distance on the boundary between a given two adjacent vertices is substantially the same as the distance on the boundary between any other two adjacent vertices.