hexagram/src/speedo.c

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

#include <hexagram/gauge.h>
#include <hexagram/speedo.h>

void hexagram_speedo_init(hexagram_speedo *speedo,
                          double x,
                          double y,
                          double radius) {
    hexagram_gauge_init(&speedo->gauge, x, y, radius,
            232.0 * (M_PI / 180.0),
            488.0 * (M_PI / 180.0));
}

void hexagram_speedo_draw_face(hexagram_speedo *speedo,
                               cairo_t *cr) {
    int i;

    cairo_select_font_face(cr, "Helvetica",
        CAIRO_FONT_SLANT_NORMAL,
        CAIRO_FONT_WEIGHT_NORMAL);

    cairo_set_font_size(cr, speedo->gauge.radius * 0.125);

    cairo_set_source_rgb(cr, 1, 1, 1);

    cairo_arc(cr,
              speedo->gauge.x,
              speedo->gauge.y,
              speedo->gauge.radius,
              0,
              2.0 * M_PI);

    cairo_stroke(cr);

    /*
     * Draw face numbers
     */
    for (i=0; i<=180; i+=20) {
        char text[5];

        snprintf(text, 4, "%02d", i);

        hexagram_gauge_draw_number(&speedo->gauge,
                                   cr,
                                   0.85,
                                   i / 180.0,
                                   text);
    }

    for (i=0; i<=180; i+=2) {
        hexagram_gauge_draw_mark(&speedo->gauge,
                                 cr,
                                 (i % 10)? 0.75: 0.7,
                                 0.8,
                                 i / 180.0);
    }
}

void hexagram_speedo_draw_needle(hexagram_speedo *speedo,
                                 cairo_t *cr,
                                 double rps) {
    double kph = (2.00152 * rps * 3600) / 1000.0,
           mph = kph * 0.621371;

    if (mph < 0) {
        mph = 0;
    } else if (mph > HEXAGRAM_SPEEDO_MAX_MPH) {
        mph = HEXAGRAM_SPEEDO_MAX_MPH;
    }

    hexagram_gauge_draw_needle(&speedo->gauge,
                               cr,
                               0.8,
                               mph / HEXAGRAM_SPEEDO_MAX_MPH);
}