hexagram/src/gauge.c

#include <stdlib.h>
#include <math.h>

#include <hexagram/gauge.h>

void hexagram_gauge_init(hexagram_gauge *gauge,
                         double x,
                         double y,
                         double radius,
                         double min_angle,
                         double max_angle) {
    gauge->x         = x;
    gauge->y         = y;
    gauge->radius    = radius;
    gauge->min_angle = min_angle;
    gauge->max_angle = max_angle;
}

void hexagram_gauge_draw_number(hexagram_gauge *gauge,
                                cairo_t *cr,
                                double radius,
                                double value,
                                const char *text) {
    double angle = gauge->min_angle
        + ((gauge->max_angle - gauge->min_angle) * value) - 1.658;

    /*
     * Draw the gauge pivot
     */
    cairo_set_source_rgb(cr, 1, 1, 1);

    cairo_arc(cr,
              gauge->x,
              gauge->y,
              gauge->radius * 0.08,
              0,
              2.0 * M_PI);

    cairo_stroke(cr);

    /*
     * Draw the needle atop the gauge pivot
     */
    cairo_set_source_rgb(cr, 1, 1, 1);

    cairo_move_to(cr,
                  gauge->x + (radius * gauge->radius) * cos(angle),
                  gauge->y + (radius * gauge->radius) * sin(angle));

    cairo_save(cr);
    cairo_rotate(cr, angle + 1.658);
    cairo_show_text(cr, text);
    cairo_stroke(cr);
    cairo_restore(cr);
}

void hexagram_gauge_draw_mark(hexagram_gauge *gauge,
                              cairo_t *cr,
                              double min_radius,
                              double max_radius,
                              double value) {
    double angle = gauge->min_angle
        + ((gauge->max_angle - gauge->min_angle) * value) - (M_PI / 2.0);

    cairo_move_to(cr,
                  gauge->x + (min_radius * gauge->radius) * cos(angle),
                  gauge->y + (min_radius * gauge->radius) * sin(angle));

    cairo_line_to(cr,
                  gauge->x + (max_radius * gauge->radius) * cos(angle),
                  gauge->y + (max_radius * gauge->radius) * sin(angle));

    cairo_stroke(cr);
}

void hexagram_gauge_draw_needle(hexagram_gauge *gauge,
                                cairo_t *cr,
                                double radius,
                                double value) {
    double angle = gauge->min_angle
        + ((gauge->max_angle - gauge->min_angle) * value) - (M_PI / 2.0);

    cairo_move_to(cr, gauge->x, gauge->y);

    cairo_set_source_rgb(cr, 0, 0.25, 1.0);

    cairo_line_to(cr,
                  gauge->x + (radius * gauge->radius) * cos(angle),
                  gauge->y + (radius * gauge->radius) * sin(angle));

    cairo_stroke(cr);
}