void interpolate(SketcherConfig &prev, SketcherConfig &next,
long prev_frame, long next_frame, long current_frame);
double nearest_point(int &ci, int &pi, coord x, coord y);
void interpolate(SketcherConfig &prev, SketcherConfig &next,
long prev_frame, long next_frame, long current_frame);
double nearest_point(int &ci, int &pi, coord x, coord y);