This paper addresses interactive function-based free-form shape modeling where relatively small formulas are used rather than thousands of polygons. Interactive modification of the function model with concurrent double-resolution visualization of the respective polygonal mesh lets us provide both the interactivity and any required level of detail leading to photo-realistic appearance of the resulting shapes. We have proposed a rendering algorithm capable of handling local shape modifications with any desired precision. Also, we proposed a few methods, which let us accelerate the final function evaluation-a common bottleneck for the function-based shape modeling. Finally, we have described applications of the interactive function-based shape modeling to photo-realistic virtual crafting.