A TEX macro color implemented almost all in PostScript language

To draw a Bezier curve in a picture environment, we propose a PostScript implementation with curveto operator. For this purpose, we need 4 points (x0, y0),(x1, y1),(x2, y2),(x3, y3) which define the tangents of the curve of figure [*].

Figure: Bézier curve
\begin{figure}\begin{center} \unitlength=1.00mm\linethickness{0.4pt} \begin{p... ...line(1,3){5}} \put(45,45){\line(1,-4){5}} \end{picture} \end{center}\end{figure}

Then, a polynomial interpolation is utilized to draw the ``best'' curve between points (x0, y0),(x3, y3). The macro is called Bezierps and admits as parameters a list of points. For TEX, this list ends when the syntatic analysor encounters the key word \endbezierps which constitutes the first parameter of the macro (for explanations about macros with mark out arguments see [2] page 201).

The body of the macro is built with a PostScript abstraction on lists – the forall operator– corresponding to the Lisp function map.

In our case, we apply curveto to a finite list of 4 points. This allows the use of only one curveto order. This construction is more efficient than a construction with curveto operators for each curve. The gain in disk space is obvious in the case of multiple curves in the application.

The drawing of figure [*] has been realized under TEXcad on a PC machine. This software from the EMTEX package doesn't allow for the drawing of Bezier curves ; it constrains us to mark explicitly the points (x0, y0) ... (x3, y3), then edit the file and insert coordinantes as parameters of the macro Bezierps. We code: 

\begin{figure}[th]
\begin{center}
\unitlength=1.00mm
\linethickness{0.4pt}
\begin{picture}(60,50)
\put(0.00,0.00){\framebox(60,50)[t]{}}
% debut de la courbe de bezier
\put(0,0){\bezierps [ [ 10 10 15 25 45 45 50 25 ]
 		] \endbezierps{.4}{3}{2}{255}{0}{0}}
\put(10,5){\makebox(0,0)[cc]{$(x_0,y_0)$}}
\put(7,25){\makebox(0,0)[cc]{$(x_1,y_1)$}}
\put(36,45){\makebox(0,0)[cc]{$(x_2,y_2)$}}
\put(50,22){\makebox(0,0)[cc]{$(x_3,y_3)$}}
\put(10,10){\makebox(0,0)[cc]{$\bullet$}}
\put(15,25){\makebox(0,0)[cc]{$\bullet$}}
\put(45,45){\makebox(0,0)[cc]{$\bullet$}}
\put(50,25){\makebox(0,0)[cc]{$\bullet$}}
\put(10,10){\line(1,3){5}}
\put(45,45){\line(1,4){5}}
\end{picture}
\caption{{\it B\'ezier curve}}
\label{figone}
\end{center}
\end{figure}