To create a curve in a Rappture C program, we make people do something like this:

    ...

    rpPutString (   lib,
                    "output.curve(f12).about.label",
                    "Fermi-Dirac Factor",
                    RPLIB_OVERWRITE );
    rpPutString (   lib,
                    "output.curve(f12).xaxis.label",
                    "Fermi-Dirac Factor",
                    RPLIB_OVERWRITE );
    rpPutString (   lib,
                    "output.curve(f12).yaxis.label",
                    "Energy",
                    RPLIB_OVERWRITE );
    rpPutString (   lib,
                    "output.curve(f12).yaxis.units",
                    "eV",
                    RPLIB_OVERWRITE );

    while (E < Emax) {
        f = 1.0/(1.0 + exp((E - Ef)/kT));
        sprintf(line,"%f %f\n",f, E);
        rpUtilsProgress((int)((E-Emin)/(Emax-Emin)*100),"Iterating");
        rpPutString(lib,"output.curve(f12).component.xy", line, RPLIB_APPEND);
        E = E + dE;
    }

    ...

Using RpCurve Object with accessor functions:

    ...
    size_t i = 0;
    size_t cnt = (Emax - E)/dE;
    double *f = (double*) malloc(cnt*sizeof(double));
    double *En = (double*) malloc(cnt*sizeof(double));
    RpCurve *c = (RpCurve*) malloc(sizeof(RpCurve));

    // assume allocation succeeded

    // register the object so lib can keep track of it, set a call back/notifier
    rpLib_register(lib,c);

    // annotate the curve
    rpCurve_path(c,"output.curve(f12)");
    rpCurve_title(c,"Fermi-Dirac Factor")
    rpCurve_xlabel(c,"Fermi-Dirac Factor");
    rpCurve_ylabel(c,"Energy");
    rpCurve_yunits(c,"eV");

    while (E < Emax) {
        f[i] = 1.0/(1.0 + exp((E - Ef)/kT));
        En[i] = E;
        rpUtilsProgress((int)((E-Emin)/(Emax-Emin)*100),"Iterating");
        E = E + dE;
    }

    // plot the value from the arrays
    rpCurve_plot(c,f,En);

    if (c) {
        free(c);
        c = NULL;
    }

    if (f) {
        free(f);
        f = NULL;
    }

    if (En) {
        free(En);
        En = NULL;
    }

    ...

The accessor functions can be replaced with annotate functions:

    rpCurve_annotate(c,"path","output.curve(f12)");
    rpCurve_annotate(c,"name","f12");
    rpCurve_annotate(c,"title","Fermi-Dirac Factor");
    rpCurve_annotate(c,"xlabel","Fermi-Dirac Factor");
    rpCurve_annotate(c,"ylabel","Energy");
    rpCurve_annotate(c,"yunits","eV");

Internally, the RpCurve object should have a hash of curve properties.
Curve Properties:

• path - full xml path of the object.
• name - name or id of the curve. This text is displayed when scrolling over the xy plot, or searching for a specific curve.
• title - title of the plot. Text to be displayed in the Results drop down menu in the gui.
• xlabel - label of the x axis.
• xunits - units of values along the x axis.
• xscale - scale of the x axis. one of linear,log.
• ylabel - label of the y axis.
• yunits - units of values along the y axis.
• yscale - scale of the y axis. one of linear,log.
• color - color of the curve.
• marker - type of marker to use.
• type - type of curve. one of column,bar,area,line(default),xyscatter,xyerror.
• group - grouping curves so they show up on the same graph.

Curve Accessor functions:

• int rpCurve_path(RpCurve *c, const char *val);
• int rpCurve_name(RpCurve *c, const char *val);
• int rpCurve_title(RpCurve *c, const char *val);
• int rpCurve_xlabel(RpCurve *c, const char *val);
• int rpCurve_xunits(RpCurve *c, const char *val);
• int rpCurve_ylabel(RpCurve *c, const char *val);
• int rpCurve_yunits(RpCurve *c, const char *val);
• int rpCurve_annotate(RpCurve *c, const char *prop, const char *val);
• int rpCurve_prop_lookup(RpCurve *c, const char *prop, const char *val);