[metapost] metafun: transparency (opacity) that doesn't add up

[Mojca Miklavec]

On 4/25/06, Stephan Hennig wrote:
> Hi,
>
> in a transparent grid I want to avoid the effect of opacity adding up at
> crossing points. This may sound strange and in some sense contradict the
> notion of transparency. However, the grid should be transparent with
> respect to other material that is drawn below it. In fact the grid and
> the other material are built as independent graphics that are both
> included from a LaTeX document (processed via pdflatex).
>
> For the grid I've tried all twelve transparency methods mentioned in the
> metafun manual, but couldn't find a suitable one. Is there any way to
> draw a uniformly colored transparent grid with MetaFun?
>
> Regards,
> Stephan Hennig
>
>
> input metafun
> beginfig(1);
> string method[];
>  method0 = "normal";
>  method1 = "multiply";
>  method2 = "screen";
>  method3 = "overlay";
>  method4 = "softlight";
>  method5 = "hardlight";
>  method6 = "colordodge";
>  method7 = "colorburn";
>  method8 = "darken";
>  method9 = "lighten";
>  method10 = "difference";
>  method11 = "exclusion";
>  pickup pencircle scaled 20bp;
>  for i=0 upto 11:
>    drawoptions(
>      shifted (150 * (i mod 4), 150 * (i div 4))
>      withcolor transparent(method[i], .1, black)
>    );
>    draw (0,0)--(100,100);
>    draw (0,100)--(100,0);

Draw a single closed curve instead:

   draw (50,50)--(0,0)--(100,100)--(50,50)--(0,100)--(100,0)--cycle;

For two separate curves you'll always get colors adding up to opacity.

Mojca

>  endfor
> endfig;
> end