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The Plotutils Package

9.3.3 Sample drawings in C++

In a previous section, there are several sample C programs that show how to draw vector graphics using libplot's C binding. See section 9.2.4 Sample drawings in C. In this section, we give a modified version of one of the C programs, showing how libplot's C++ binding, i.e., libplotter, can be used similarly.

The following C++ program draws an intricate and beautiful path (Bill Gosper's "C" curve).

#include <plotter.h> const int maxorder = 12; void draw_c_curve (Plotter& plotter, double dx, double dy, int order) { if (order >= maxorder) plotter.fcontrel (dx, dy); // continue path along (dx, dy) else { draw_c_curve (plotter, 0.5 * (dx - dy), 0.5 * (dx + dy), order + 1); draw_c_curve (plotter, 0.5 * (dx + dy), 0.5 * (dy - dx), order + 1); } } int main () { // set a Plotter parameter PlotterParams params; params.setplparam ("PAGESIZE", (char *)"letter"); PSPlotter plotter(cin, cout, cerr, params); // declare Plotter if (plotter.openpl () < 0) // open Plotter { cerr << "Couldn't open Plotter\n"; return 1; } plotter.fspace (0.0, 0.0, 1000.0, 1000.0); // specify user coor system plotter.flinewidth (0.25); // line thickness in user coordinates plotter.pencolorname ("red"); // path will be drawn in red plotter.erase (); // erase Plotter's graphics display plotter.fmove (600.0, 300.0); // position the graphics cursor draw_c_curve (plotter, 0.0, 400.0, 0); if (plotter.closepl () < 0) // close Plotter { cerr << "Couldn't close Plotter\n"; return 1; } return 0; }

The above is a straightforward translation of the corresponding C program. Here, plotter is declared as an instance of the PSPlotter class, which will write Postscript graphics to the output stream cout. The graphics are drawn by invoking member functions.