What you see whilst drawing, is what you need for drawing.

The figure below is from Visuomotor characterization of eye movements in a drawing task. Ruben Coen-Cagli, Paolo Coraggio, Paolo Napoletano, Odelia Schwartz, Mario Ferraro and Giuseppe Boccignone. Vision Research, 49, Issue 8, 2009, pp. 810-818. 


This is an interesting eye-tracking study that quantifies how much more you focus on an object when you are drawing it versus just viewing it. 

" We find that a peculiar feature of the drawing behavior is that the gaze does not move back and forth among different objects, but proceeds sequentially, and most fixations on an object are executed within a time interval in which no fixations occur on other objects."

In addition the proportion of inter-object saccades to total saccades (a saccade is a  quick, simultaneous movement of both eyes in the same direction) is four times higher for free viewing (c) versus drawing (d).