[PD] log function in slider

[Alexandre Torres Porres]

so you say this is actually the section of the code I'm looking for to make
the conversion I want, right?

======

static void hslider_set(t_hslider *x, t_floatarg f)    /* bugfix */

{

    double g;


    if(x->x_gui.x_isa.x_reverse)    /* bugfix */

    {

        if(f > x->x_min)

            f = x->x_min;

        if(f < x->x_max)

            f = x->x_max;

    }

    else

    {

        if(f > x->x_max)

            f = x->x_max;

        if(f < x->x_min)

            f = x->x_min;

    }

    if(x->x_lin0_log1)

        g = log(f/x->x_min)/x->x_k;

    else

        g = (f - x->x_min) / x->x_k;

    x->x_val = (int)(100.0*g + 0.49999);

    x->x_pos = x->x_val;

    (*x->x_gui.x_draw)(x, x->x_gui.x_glist, IEM_GUI_DRAW_MODE_UPDATE);

}


2014-03-17 4:07 GMT-03:00 Jonathan Wilkes <jancsika at yahoo.com>:

> AFAICT vslider is saving something like a slider position, and your
> expression above (along with the code I posted) is for getting back the
> original value from it.  If you send it something between 0.01 and 1 you'll
> get a curve that's inverted from the one you're after.  If you send it a
> slider position-- something like another [expr] based on the code inside
> vslider_set-- you'll get back (roughly) the same value you input.
>
> But I'm still stuck on why vslider_bang is doing any math at all.  Why
> should it be more complex than "if bang then output stored value"?
> (Setting aside sending to receive symbols for the moment.)
>
> -Jonathan
>
>
>
>   On Monday, March 17, 2014 1:21 AM, Alexandre Torres Porres <
> porres at gmail.com> wrote:
>  Hi Roman. This is turning out trickier than I thought. A friend
> explained the code to me and got to the following equation, with min/max
> values as 0.01 and 1 respectively.
>
> [expr 0.01 * exp((log(1 / 0.01) / 0.01) * $f1 * 0.01)]
>
> For what I've checked, it seems to behave like your patch. But it doesn't
> do the trick I'm looking for yet. I sent a patch earlier, and I'm sending
> it back again.
>
> The goal is to connect a linear slider to an [expr] (with this so called
> "log" function) and then to another linear slider. The idea then is that
> this second slider behaves as one that was set as being "log".
>
> In the patch attached I was able to emulate it poorly with [pow 0.25], but
> that was before reaching the list. See that if I use this expr function
> from the code or your patch it presents quite a different behavior.
>
> maybe it is some sort of inversion of this equation, not sure. Apparently
> this code converts the "log" function values to linear and I'm hoping to
> get the exact opposite. Got it?
>
> Thanks for looking into this
>
>
> 2014-03-12 4:38 GMT-03:00 Roman Haefeli <reduzent at gmail.com>:
>
> On Don, 2014-03-06 at 21:37 -0300, Alexandre Torres Porres wrote:
> > hi folks, out of curiosity, what's the exact log function used in the
> > slider? I'd like to emulate it.
>
> I am not sure, if this is what you want. It converts the incoming linear
> range between 0 and 1 to a logarithmic range specified by $1 and $2,
> respectively by the second and third inlet. They behave like the lower
> and upper bound specified in the [vslider]/[hslider] classes.
>
> https://raw.github.com/reduzent/netpd2-patches/master/abs/rh_scalelog.pd
>
>
> Roman
>
>
>
>
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