/*
 * plot.c - function plotting.  Pass in an arbitrary function to plot.
 * To make the program easier, the function plotted is x=f(y) instead of
 * y=f(x).  All function values and parameters are type double.
 */

#include <stdio.h>
#include <math.h>
#include "plot.h"


void plot(double (*f)(double x), double size)
{
    int i;
    extern int xvalue(int y);
    extern void plot_one(int x, int blankchar, int centrechar);

    for (i = 10; i >= -10; i--) {
        double y = size * i / 10;
        int x = (int)floor(10 / size * 2 * f(y) + 0.5);
        if (i == 0)
            plot_one(x, '-', '+');
        else
            plot_one(x, ' ', '|');
    }
}


/*
 * plot one row -- spaces, maybe axes, maybe an asterisk.
 * 'x' is a value from -20 to 20 which says where the asterisk goes, or
 * outside that range if there isn't one.  blankchar says what goes where
 * there isn't anything; usually a space, but '-' for the x axis.
 * centrechar says what to plot for the y axis if there isn't an asterisk
 * there; usually '|', but '+' for the origin.
 */
void plot_one(int x, int blankchar, int centrechar)
{
    int i;
    for (i = -20; i <= 20; i++) {
        if (i == x)
            putchar('*');
        else if (i == 0)
            putchar(centrechar);
        else
            putchar(blankchar);
    }
    putchar('\n');
}