1. In a computer-implemented image generation system, wherein image elements are provided to a processor for rendering into an image and wherein at least some of the image elements correspond to simulated paint strokes, a method comprising: receiving parameters of a three-dimensional scalar field defining a three-dimensional virtual space; receiving a selection of a three-dimensional object in the three-dimensional scalar field; receiving from an input device two-dimensional positions of simulated paint strokes; associating the simulated paint strokes with the three-dimensional object positioned in the three-dimensional scalar field, wherein the simulated paint strokes do not alter the shape of the three-dimensional object; and based on the three-dimensional scalar field and two-dimensional positions of the simulated paint strokes, determining depth information for the simulated paint strokes, thereby positioning the simulated paint strokes in the three-dimensional virtual space, usable as representations for image elements to be provided to the processor for rendering into an image.