Improve time marker handling and add printing of some time labels

We now draw time markers at most every 5 min, but no more than 12 markers.
For convenience we do 5, 10, 15 or 30 min intervals.
This allows for 6h dives - enough (I hope) for even the craziest divers -
but just in case, for those 8h depth-record-breaking dives, we double the
interval if this still doesn't get us to 12 or fewer time markers.

We label the first and then every other time marker with the minute text.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

diff --git a/profile.c b/profile.c
index 7832dccafd36242c7835f45ae1ac9e115a3d13e4..6c1e8ce426d63cc3f68262f9e61a75458492c1ad 100644 (file)
--- a/profile.c
+++ b/profile.c
@@ -299,23 +299,43 @@ static void plot_minmax_profile(struct graphics_context *gc, struct plot_info *p
 
 static void plot_depth_profile(struct graphics_context *gc, struct plot_info *pi)
 {
-       int i;
+       int i, incr;
        cairo_t *cr = gc->cr;
        int sec, depth;
        struct plot_data *entry;
        int maxtime, maxdepth, marker;
+       int increments[4] = { 5*60, 10*60, 15*60, 30*60 };
 
        /* Get plot scaling limits */
        maxtime = get_maxtime(pi);
        maxdepth = get_maxdepth(pi);
 
-       /* Time markers: every 5 min */
+       /* Time markers: at most every 5 min, but no more than 12 markers
+        * and for convenience we do 5, 10, 15 or 30 min intervals.
+        * This allows for 6h dives - enough (I hope) for even the craziest
+        * divers - but just in case, for those 8h depth-record-breaking dives,
+        * we double the interval if this still doesn't get us to 12 or fewer
+        * time markers */
+       i = 0;
+       while (maxtime / increments[i] > 12 && i < 4)
+               i++;
+       incr = increments[i];
+       while (maxtime / incr > 12)
+               incr *= 2;
+
        gc->leftx = 0; gc->rightx = maxtime;
        gc->topy = 0; gc->bottomy = 1.0;
-       for (i = 5*60; i < maxtime; i += 5*60) {
+       set_source_rgba(gc, 1, 1, 1, 0.5);
+       for (i = incr; i < maxtime; i += incr) {
                move_to(gc, i, 0);
                line_to(gc, i, 1);
        }
+       cairo_stroke(cr);
+
+       /* now the text on every second time marker */
+       text_render_options_t tro = {10, 0.2, 1.0, 0.2, CENTER, TOP};
+       for (i = incr; i < maxtime; i += 2 * incr)
+               plot_text(gc, &tro, i, 1, "%d", i/60);
 
        /* Depth markers: every 30 ft or 10 m*/
        gc->leftx = 0; gc->rightx = 1.0;