We put the picture into a box so that we will be able to measure its dimensions. Now, we must be careful not to introduce strange stuff into the box that will ruin the measurements. In DraTeX we might be less careful because spaces are ignored due to their catcode of 9.
<..put picture in box..>
\setbox\:box=-_-_-
<..measure dimension of drawing..>
{\:X=\wd\:box \:Y=\ht\:box \advance\:Y by\dp\:box
\xdef\DrawWidth{\:InCons\:X}%
\xdef\DrawHeight{\:InCons\:Y}%
\xdef\MinDrawX{\:InCons\:LBorder}%
\:X=\:UBorder \xdef\MaxDrawy{\:InCons\:X}%
}%
-_-_-