+
+
+/* Adjust tick to be a sensible value
+ ie: ... 0.1,0.2,0.5, 1,2,5, 10,20,50 ... */
+double
+chart_rounded_tick(double tick)
+{
+
+ int i;
+
+ double diff = DBL_MAX;
+ double t = tick;
+
+ static const double standard_ticks[] = {1, 2, 5, 10};
+
+ const double factor = pow(10,ceil(log10(standard_ticks[0] / tick))) ;
+
+ for (i = 3 ; i >= 0 ; --i)
+ {
+ const double d = fabs( tick - standard_ticks[i] / factor ) ;
+
+ if ( d < diff )
+ {
+ diff = d;
+ t = standard_ticks[i] / factor ;
+ }
+ }
+
+ return t;
+
+}
+
+
+/* Set the scale for the abscissa */
+void
+chart_write_xscale(struct chart *ch, double min, double max, int ticks)
+{
+ double x;
+
+ const double tick_interval =
+ chart_rounded_tick( (max - min) / (double) ticks);
+
+ ch->x_max = ceil( max / tick_interval ) * tick_interval ;
+ ch->x_min = floor ( min / tick_interval ) * tick_interval ;
+
+ ch->abscissa_scale = fabs(ch->data_right - ch->data_left) /
+ fabs(ch->x_max - ch->x_min);
+
+ for(x = ch->x_min ; x <= ch->x_max; x += tick_interval )
+ {
+ draw_tick (ch, TICK_ABSCISSA,
+ (x - ch->x_min) * ch->abscissa_scale, "%g", x);
+ }
+
+}
+
+
+/* Set the scale for the ordinate */
+void
+chart_write_yscale(struct chart *ch, double smin, double smax, int ticks)
+{
+ double y;
+
+ const double tick_interval =
+ chart_rounded_tick( (smax - smin) / (double) ticks);
+
+ ch->y_max = ceil ( smax / tick_interval ) * tick_interval ;
+ ch->y_min = floor ( smin / tick_interval ) * tick_interval ;
+
+ ch->ordinate_scale =
+ fabs(ch->data_top - ch->data_bottom) / fabs(ch->y_max - ch->y_min) ;
+
+ for(y = ch->y_min ; y <= ch->y_max; y += tick_interval )
+ {
+ draw_tick (ch, TICK_ORDINATE,
+ (y - ch->y_min) * ch->ordinate_scale, "%g", y);
+ }
+
+}
+