[gtkextra] Autoticks

[Emmanuel P. <emm...@un...>]

I'm not sure this is not implemented in the current GtkExtra API, but I
use the following function to calculate a space between two ticks which
is easily readable (ie: every 1Ex, 2Ex, 5Ex)


void
auto_tick_step	( int tick_count, double minimum, double maximum, double*
major_tick_step, int *minor_tick_number) {

double log_tick_step,test_tick_step,round_log_tick_step,round_tick_step;

  log_tick_step=log10(fabs(maximum-minimum)/(double) tick_count);
  test_tick_step=log_tick_step-floor(log_tick_step);
  round_log_tick_step=0.0;
  if ((test_tick_step>0.0)&&(test_tick_step<=log10(2))) {
    round_log_tick_step=log10(2);
    *minor_tick_number=9;
  }
  if ((test_tick_step>log10(2))&&(test_tick_step<=log10(5))) {
    round_log_tick_step=log10(5);
    *minor_tick_number=4;
  }
  if ((test_tick_step>log10(5))&&(test_tick_step<=log10(10))) {
    round_log_tick_step=log10(10);
    *minor_tick_number=9;
  }

 
round_tick_step=exp((round_log_tick_step+floor(log_tick_step))*log(10));

  *major_tick_step=round_tick_step;

}

params: 
tick_count : the maximum number of ticks.
minimum and maximum : min/max of the axis.

returns:
major_tick_step : step between two ticks.
minor_tick_number : number of minor ticks between two major ticks. 

example:

  tick_count=10  minimum=810 maximum=1200 -> major_tick_step=50
minor_tick_number=4


If a similar function does not exist, it would be great if it should bet
implemented in GtkExtra.

  Emmanuel.