Re: x11 palette inaccuracy?

[Daniel J S. <dan...@ie...>]

On 08/31/2013 04:19 PM, Juhász Péter wrote:
> Dear gnuplot list,
>
> continuing my recent series "exposing possible bugs by fun, useless
> scripts", here is a nice plasma effect:
>
>
> set term x11
> set sa 50
> set isosa 50
> set pm3d
> unset surface
> set view map
>
> plasma(x,y) = sin(x/.8)+sin(y/1.6)+sin((x+y)/1.9)
> pal(t) = sprintf("set pal model HSV functions frac(gray+%f),0.5,1", t)
> frac(x)= x-int(x)
> t = 0
> while(t<10){eval pal(t); t= t+0.01; pr t; splot plasma(x,y)}
>
>
> With the x11 terminal I notice that there is "snowing" on the picture,
> that is, some of the pm3d rectangles have incorrect color in certain
> frames. Rounding or accuracy effect?
>
> I don't know if this is significant at all, but it doesn't show with the
> wxt or qt terminals.

OK, I finally broke out of the hypnotic trance...

The snow effect appears to happen when the color of the "pixel" is 
predominantly red.  Assuming the order of the triplet is RGB with red 
being most significant, it could be that the upper-most palette is 
incorrect, the index is pointing outside the palatte, or there is some 
time of sign/unsigned issue unaccounted for, or all of the above.  I'd 
have to guess it is an end-of-palette issue because otherwise I suspect 
we'd have seen this issue show up in some other way.

Dan