#include <cairo.h>
#include <math.h>
#include <stdio.h>

int main()
{
    double width = 320, height = 240;
    double f, delta = 0.125;
    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
    cairo_t *crc = cairo_create(surface);
    cairo_text_extents_t extents;
    cairo_font_options_t* font;

    // Set up font  (face is second field in 'xlsfonts'; first field is foundry)
    font = cairo_font_options_create();
    cairo_font_options_set_antialias(font, CAIRO_ANTIALIAS_SUBPIXEL);
    cairo_set_font_options(crc, font);
    cairo_select_font_face(crc, "nimbus sans l", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
    cairo_set_font_size(crc, 16);
    cairo_font_options_destroy(font);

    // Background
    cairo_rectangle(crc, 0, 0, width, height);
    cairo_set_source_rgb(crc, 1, 1, 1);
    cairo_fill(crc);

    // Fill
    cairo_move_to(crc, 0, 220);
    for (f = -4; f < 4; f += delta)
    {
        double v = exp(-f * f / 2) / sqrt(2 * M_PI);
        cairo_line_to(crc, width * (f + 4) / 8, 220 - v * height);
    }
    cairo_close_path(crc);
    cairo_set_source_rgb(crc, 122 / 255.0, 143 / 255.0, 248 / 255.0);
    cairo_fill(crc);

    // Graph
    cairo_move_to(crc, 0, 220);
    for (f = -4; f < 4; f += delta)
    {
        double v = exp(-f * f / 2) / sqrt(2 * M_PI);
        cairo_line_to(crc, width * (f + 4) / 8, 220 - v * height);
    }
    cairo_set_line_width(crc, 2);
    cairo_set_source_rgb(crc, 7 / 255.0, 16 / 255.0, 141 / 255.0);
    cairo_stroke(crc);

    // Vertical Axis
    cairo_set_source_rgb(crc, 0, 0, 0);
    cairo_move_to(crc, width / 2, 0);
    cairo_line_to(crc, width / 2, height);
    cairo_stroke(crc);

    // Horizontal Axis
    cairo_move_to(crc, 0, 220);
    cairo_line_to(crc, width, 220);
    cairo_stroke(crc);

    // Horizontal Ticks
    cairo_set_line_width(crc, 1);
    for (f = -4; f < 4; f++)
    {
        cairo_move_to(crc, width * (f + 4) / 8, 220 - 5);
        cairo_line_to(crc, width * (f + 4) / 8, 220 + 5);
        cairo_stroke(crc);

        if (f > -4 && f != 0 && f < +4)
        {
            char str[] = "+3";
            if (f > 0)
                sprintf(str, "%d", (int) f);
            else
                sprintf(str, "%d", (int) f);
            cairo_text_extents(crc, str, &extents);
            cairo_move_to(crc, width * (f + 4) / 8 - extents.width / 2, 220 + 7 + extents.height);
            cairo_show_text(crc, str);
        }
    }

    // Vertical Ticks
    for (f = +1; f >= -1; f -= 0.1)
    {
        cairo_move_to(crc, width / 2 - 5, 220 + f * height);
        cairo_line_to(crc, width / 2 + 5, 220 + f * height);
        cairo_stroke(crc);
    }

    cairo_text_extents(crc, "0.5", &extents);
    cairo_move_to(crc, width / 2 + 7, 220 - 0.5 * height + extents.height / 2);
    cairo_show_text(crc, "0.5");

    cairo_surface_write_to_png(surface, "gauss.png");
    return 0;
}