[rrd-developers] Re: rrd_graph patch for nice log gridlines

[Tobias Oetiker]

Today Beat Zahnd wrote:

> Beat Zahnd wrote:
> >
> > Is there some rounding in ytr().
> >
>
> There seems to be a problem with 'pixie' in ytr(). 'pixie' is only
> defined if 'value' is a NAN?!?!

Hi Beat,

this is a trick

as you can see on line 2508 of rrd_graph.c there is an explicit
call to ytr with value NAN ... this is used to initialize pixie.

cheers
tobi
>
> Regards, Beat
>
> /* translate data values into y coordinates */
> double
> ytr(image_desc_t *im, double value){
>       static double pixie;
>       double yval;
>       if (isnan(value)){
>         if(!im->logarithmic)
>           pixie = (double) im->ysize / (im->maxval - im->minval);
>         else
>           pixie = (double) im->ysize / (log10(im->maxval) -
> log10(im->minval));
>         yval = im->yorigin;
>       } else if(!im->logarithmic) {
>         yval = im->yorigin - pixie * (value - im->minval);
>       } else {
>         if (value < im->minval) {
>           yval = im->yorigin;
>         } else {
>           yval = im->yorigin - pixie * (log10(value) - log10(im->minval));
>         }
>       }
>       /* make sure we don't return anything too unreasonable. GD lib can
>          get terribly slow when drawing lines outside its scope. This is
>          especially problematic in connection with the rigid option */
>       if (! im->rigid) {
>         /* keep yval as-is */
>       } else if (yval > im->yorigin) {
>         yval = im->yorigin+2;
>       } else if (yval < im->yorigin - im->ysize){
>         yval = im->yorigin - im->ysize - 2;
>       }
>       return yval;
> }
>
>
>

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